Java Hibernate 5 Tutorial for Beginners

1- Introduction

This document is based on:
  • Hibernate 5.2.2.Final

  • Eclipse 4.6 (MARS)

History:
  • Last Update: 14-09-2016 (dd-MM-yyyy).
  1. Starting in 5.0 Hibernate Spatial is part of the Hibernate project so we can handle GIS data too.
  2. The Java 8 Date and Time types are supported in domain model mappings. The mapping between the standard SQL Date/Time types and the supported Java 8 Date/Time class types looks as follows;
    • DATE: java.time.LocalDate
    • TIME: java.time.LocalTime, java.time.OffsetTime
    • TIMESTAMP: java.time.Instant, java.time.LocalDateTime, java.time.OffsetDateTime and java.time.ZonedDateTime
  3. The bytecode enhancement mechanism was redesigned from scratch, and Hibernate features both a Maven and a Gradle plugin. There are three main aspects which we can enhance with bytecode instrumentation:
    • Lazy initialization: Fields can be declared as LAZY and they will be fetched only when being accessed for the first time.
    • Dirty checking: Entities are enhanced so that they can keep track of all the properties that get changed after being loaded in a Persistence Context.
    • Bidirectional associations: It's possible to synchronize both sides of a bidirectional association automatically, even if the developer only updates a single side.
  4. Hibernate's native APIs (Session, etc) have been updated to use generic typed. No need to cast when fetching entities.
  5. Hibernate 5.0 expends this to a broader set of types (e.g. UUID).
  6. Second-level cache by reference. This feature enables direct storage of entity references into the second level cache for immutable entities.

2- Preparing the Database

Hibernate is a library formed in order to work with all types of DB, it does not depend on any types of DB you choose". If Java is " Write once, run anywhere", Hibernate will be " Write one, run on all types of DB".
In the post, I use the simplehr, which is a simple database used in lots of tutorials on o7planning. You can create it with one of the databases such as Oracle, MySQL or SQL Server. Let's see the guideline below:

3- Create Maven Project & Declare library

Here, I create a Maven project and declare the Hibernate libraries in pom.xml.
  • File/New/Other...
Project is created.
In pom.xml, I delare the Hibernate 5 library, and the JDBC libraries for the various database types such as Oracle, MySQL and SQL Server.
pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
               http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.o7planning</groupId>
    <artifactId>HibernateTutorial</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>HibernateTutorial</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>


    <repositories>
        <!-- Repository for ORACLE JDBC Driver -->
        <repository>
            <id>codelds</id>
            <url>https://code.lds.org/nexus/content/groups/main-repo</url>
        </repository>
    </repositories>
   
   
    <dependencies>


        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

        <!-- Hibernate Core -->
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.2.2.Final</version>
        </dependency>


        <!-- MySQL JDBC driver -->
        <!-- http://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.34</version>
        </dependency>

        <!-- Oracle JDBC driver -->
        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc6</artifactId>
            <version>11.2.0.3</version>
        </dependency>

        <!-- SQLServer JDBC driver (JTDS) -->
        <!-- http://mvnrepository.com/artifact/net.sourceforge.jtds/jtds -->
        <dependency>
            <groupId>net.sourceforge.jtds</groupId>
            <artifactId>jtds</artifactId>
            <version>1.3.1</version>
        </dependency>

    </dependencies>
   
</project>

 

4- Entity classes

We create class Entity. Each Entity describes a table in DB. Wait a minute, don't talk about anything in those classes.
  1. Department
  2. Employee
  3. SalaryGrade
  4. Timekeeper
Department.java
package org.o7planning.tutorial.hibernate.entities;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "DEPARTMENT",
  uniqueConstraints = { @UniqueConstraint(columnNames = { "DEPT_NO" }) })
public class Department {

private Integer deptId;
private String deptNo;

private String deptName;
private String location;
private Set<Employee> employees = new HashSet<Employee>(0);

public Department() {
}

public Department(Integer deptId, String deptName, String location) {
   this.deptId = deptId;
   this.deptNo = "D" + this.deptId;
   this.deptName = deptName;
   this.location = location;
}

@Id
@Column(name = "DEPT_ID")
public Integer getDeptId() {
   return deptId;
}

public void setDeptId(Integer deptId) {
   this.deptId = deptId;
}

@Column(name = "DEPT_NO", length = 20, nullable = false)
public String getDeptNo() {
   return deptNo;
}

public void setDeptNo(String deptNo) {
   this.deptNo = deptNo;
}

@Column(name = "DEPT_NAME", nullable = false)
public String getDeptName() {
   return deptName;
}

public void setDeptName(String deptName) {
   this.deptName = deptName;
}

@Column(name = "LOCATION")
public String getLocation() {
   return location;
}

public void setLocation(String location) {
   this.location = location;
}

@OneToMany(fetch = FetchType.LAZY, mappedBy = "department")
public Set<Employee> getEmployees() {
   return employees;
}

public void setEmployees(Set<Employee> employees) {
   this.employees = employees;
}
}
Employee.java
package org.o7planning.tutorial.hibernate.entities;

import java.util.Date;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "EMPLOYEE",
   uniqueConstraints = { @UniqueConstraint(columnNames = { "EMP_NO" }) })
public class Employee {
private Long empId;
private String empNo;

private String empName;
private String job;
private Employee manager;
private Date hideDate;
private Float salary;
private byte[] image;

private Department department;
private Set<Employee> employees = new HashSet<Employee>(0);

public Employee() {
}

public Employee(Long empId, String empName, String job, Employee manager,
        Date hideDate, Float salary, Float comm, Department department) {
    this.empId = empId;
    this.empNo = "E" + this.empId;
    this.empName = empName;
    this.job = job;
    this.manager = manager;
    this.hideDate = hideDate;
    this.salary = salary;
    this.department = department;
}

@Id
@Column(name = "EMP_ID")
public Long getEmpId() {
    return empId;
}

public void setEmpId(Long empId) {
    this.empId = empId;
}

@Column(name = "EMP_NO", length = 20, nullable = false)
public String getEmpNo() {
    return empNo;
}

public void setEmpNo(String empNo) {
    this.empNo = empNo;
}

@Column(name = "EMP_NAME", length = 50, nullable = false)
public String getEmpName() {
    return empName;
}

public void setEmpName(String empName) {
    this.empName = empName;
}

@Column(name = "JOB", length = 30, nullable = false)
public String getJob() {
    return job;
}

public void setJob(String job) {
    this.job = job;
}

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "MNG_ID")
public Employee getManager() {
    return manager;
}

public void setManager(Employee manager) {
    this.manager = manager;
}

@Column(name = "HIRE_DATE", nullable = false)
@Temporal(TemporalType.DATE)
public Date getHideDate() {
    return hideDate;
}

public void setHideDate(Date hideDate) {
    this.hideDate = hideDate;
}

@Column(name = "SALARY", nullable = false)
public Float getSalary() {
    return salary;
}

public void setSalary(Float salary) {
    this.salary = salary;
}

@Column(name = "IMAGE", length = 1111111, nullable = true)
@Lob
public byte[] getImage() {
    return image;
}

public void setImage(byte[] image) {
    this.image = image;
}

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "DEPT_ID", nullable = false)
public Department getDepartment() {
    return department;
}

public void setDepartment(Department department) {
    this.department = department;
}

@OneToMany(fetch = FetchType.LAZY, mappedBy = "empId")
public Set<Employee> getEmployees() {
    return employees;
}

public void setEmployees(Set<Employee> employees) {
    this.employees = employees;
}

}
SalaryGrade.java
package org.o7planning.tutorial.hibernate.entities;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "SALARY_GRADE")
public class SalaryGrade {
 private Integer grade;
 private Float lowSalary;
 private Float highSalary;

 public SalaryGrade() {
 }

 public SalaryGrade(Integer grade, Float lowSalary, Float highSalary) {
     this.grade = grade;
     this.lowSalary = lowSalary;
     this.highSalary = highSalary;
 }

 @Id
 @Column(name = "GRADE")
 public Integer getGrade() {
     return grade;
 }

 public void setGrade(Integer grade) {
     this.grade = grade;
 }

 @Column(name = "LOW_SALARY", nullable = false)
 public Float getLowSalary() {
     return lowSalary;
 }

 public void setLowSalary(Float lowSalary) {
     this.lowSalary = lowSalary;
 }

 @Column(name = "HIGH_SALARY", nullable = false)
 public Float getHighSalary() {
     return highSalary;
 }

 public void setHighSalary(Float highSalary) {
     this.highSalary = highSalary;
 }
}
Timekeeper.java
package org.o7planning.tutorial.hibernate.entities;

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "TIMEKEEPER")
public class Timekeeper {
  public static final char IN = 'I';
  public static final char OUT = 'O';

  private String timekeeperId;

  private Date dateTime;

  private Employee employee;

  // 'I' or 'O'
  private char inOut;

  @Id
  @GeneratedValue(generator = "uuid")
  @GenericGenerator(name = "uuid", strategy = "uuid2")
  @Column(name = "Timekeeper_Id", length = 36)
  public String getTimekeeperId() {
      return timekeeperId;
  }

  public void setTimekeeperId(String timekeeperId) {
      this.timekeeperId = timekeeperId;
  }

  @Column(name = "Date_Time", nullable = false)
  @Temporal(TemporalType.TIMESTAMP)
  public Date getDateTime() {
      return dateTime;
  }

  public void setDateTime(Date dateTime) {
      this.dateTime = dateTime;
  }

  @ManyToOne(fetch = FetchType.LAZY)
  @JoinColumn(name = "EMP_ID", nullable = false)
  public Employee getEmployee() {
      return employee;
  }

  public void setEmployee(Employee employee) {
      this.employee = employee;
  }

  @Column(name = "In_Out", nullable = false, length = 1)
  public char getInOut() {
      return inOut;
  }

  public void setInOut(char inOut) {
      this.inOut = inOut;
  }

}

5- Configure Hibernate

The purpose is that Hibernate can read Database as well as declare the list of Entities you created in the previous steps.
Create hibernate.cfg.xml configuration file located in src/main/java.
hibernate.cfg.xml (ORACLE)
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
                          "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
 <session-factory>

     <property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>
     <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
     <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:db11g</property>
     <property name="hibernate.connection.username">simplehr</property>
     <property name="hibernate.connection.password">12345</property>
     <property name="hibernate.show_sql">true</property>
     <property name="hibernate.connection.release_mode">auto</property>
     <property name="current_session_context_class">thread</property>
     <property name="hibernate.connection.autoReconnect">true</property>


     <mapping class="org.o7planning.tutorial.hibernate.entities.Department" />
     <mapping class="org.o7planning.tutorial.hibernate.entities.Employee" />
     <mapping class="org.o7planning.tutorial.hibernate.entities.SalaryGrade" />
     <mapping class="org.o7planning.tutorial.hibernate.entities.Timekeeper" />

 </session-factory>

</hibernate-configuration>
hibernate.cfg.xml (MySQL)
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

  <session-factory>
      <!-- Database connection settings -->
      <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
      <property name="connection.url">jdbc:mysql://tran-vmware:3306/simplehr?serverTimezone=UTC</property>
      <property name="connection.username">root</property>
      <property name="connection.password">1234</property>

      <!-- JDBC connection pool (use the built-in) -->
      <property name="connection.pool_size">1</property>

      <!-- SQL dialect -->
      <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

      <!-- Enable Hibernate's automatic session context management -->
      <property name="current_session_context_class">thread</property>

      <!-- Disable the second-level cache -->
      <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>

      <!-- Echo all executed SQL to stdout -->
      <property name="show_sql">true</property>

      <mapping class="org.o7planning.tutorial.hibernate.entities.Department" />
      <mapping class="org.o7planning.tutorial.hibernate.entities.Employee" />
      <mapping class="org.o7planning.tutorial.hibernate.entities.SalaryGrade" />
      <mapping class="org.o7planning.tutorial.hibernate.entities.Timekeeper" />

  </session-factory>

</hibernate-configuration>
hibernate.cfg.xml (SQL Server)
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
      "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
      "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
    <session-factory>
        <!-- Database connection settings -->
        <property name="connection.driver_class">net.sourceforge.jtds.jdbc.Driver</property>
        <property name="connection.url">jdbc:jtds:sqlserver://localhost:1433/simplehr;instance=SQLEXPRESS</property>
        <property name="connection.username">sa</property>
        <property name="connection.password">1234</property>

        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">1</property>

        <!-- SQL dialect -->
        <property name="dialect">org.hibernate.dialect.SQLServerDialect</property>

        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</property>

        <!-- Disable the second-level cache -->
        <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>

        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>

        <mapping class="org.o7planning.tutorial.hibernate.entities.Department" />
        <mapping class="org.o7planning.tutorial.hibernate.entities.Employee" />
        <mapping class="org.o7planning.tutorial.hibernate.entities.SalaryGrade" />
        <mapping class="org.o7planning.tutorial.hibernate.entities.Timekeeper" />

    </session-factory>
</hibernate-configuration>
Each Database has an individual Dialect
For example:
Dialect for Oracle:
  • org.hibernate.dialect.Oracle10gDialect (Dùng cho 10g &11g)
  • org.hibernate.dialect.Oracle12cDialect
Dialect for SQL Server:
  • org.hibernate.dialect.SQLServerDialect
  • org.hibernate.dialect.SQLServer2012Dialect
  • org.hibernate.dialect.SQLServer2008Dialect
Dialect for MySQL
  • org.hibernate.dialect.MySQLDialect
  • org.hibernate.dialect.MySQL5Dialect
Note: org.hibernate.dialect.Oracle10gDialect be used for both Oracle 10g, 11g, 12c.

What is Dialect?

Dialect is a class showing Hibernate the way to convert the data types of Database to the data type of Java and vice versa. Also, it is used to define the way that converts the functions of HSQL (Hibernate SQL) to the functions of Database
Java SQL Type Oracle My SQL SQL Server
Types.BIT number(1,0) bit bit
Types.BIGINT number(19,0) bigint bigint
Types.DATE date date date
 .......      
Types.CLOB clob longtext varchar(MAX)
Types.BLOB blob longblob varbinary(MAX)

6- SessionFactory

HibernateUtils.java
package org.o7planning.tutorial.hibernate;

import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.service.ServiceRegistry;

public class HibernateUtils {

    private static final SessionFactory sessionFactory = buildSessionFactory();

    // Hibernate 5:
    private static SessionFactory buildSessionFactory() {
        try {
            // Create the ServiceRegistry from hibernate.cfg.xml
            ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()//
                    .configure("hibernate.cfg.xml").build();

            // Create a metadata sources using the specified service registry.
            Metadata metadata = new MetadataSources(serviceRegistry).getMetadataBuilder().build();

            return metadata.getSessionFactoryBuilder().build();
        } catch (Throwable ex) {
        
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    public static void shutdown() {
        // Close caches and connection pools
        getSessionFactory().close();
    }

}

7- Hibernate Query Language (HQL)

Hibernate using Hibernate Query Language ( HQL) to query data. HQL is a little bit different from SQL you have known before.

SQL:
  • Query in the table.
HQL:
  • Query in the Entity class.
-- SQL
-- This is a SQL query in table DEPARTMENT.
Select d.DEPT_NO, d.DEPT_NAME from DEPARTMENT d;

-- HQL
-- This is a HQL query in Entity Department.
Select d.deptNo, d.deptName from Department d;

-- Query Object
Select d from Department d;

The rules of operation of Hibernate:

Your application writes HQL. During the operation, Hibernate by itself is aware of the Database type  it works with, and it automatically converts HQL into equivalent SQLs to DB types. In fact, we know that there are some differences of SQL syntax among various Database types.
You can reference HQL syntax at:

8- Query data with Hibernate

There are many ways to query data in Hibernate. In this part, I will introduce some typical ways to query data.

8.1- Query Object using HQL

The first example, using HQL query objects (Entity):
QueryObjectDemo.java
package org.o7planning.tutorial.hibernate.query;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class QueryObjectDemo {

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();

       try {
           
           // All the action with DB via Hibernate
           // must be located in one transaction.
           // Start Transaction.            
           session.getTransaction().begin();

   
           
           // Create an HQL statement, query the object.
           // Equivalent to the SQL statement:
           // Select e.* from EMPLOYEE e order by e.EMP_NAME, e.EMP_NO
           String sql = "Select e from " + Employee.class.getName() + " e "
                   + " order by e.empName, e.empNo ";

  
           // Create Query object.
           Query<Employee> query = session.createQuery(sql);

   
           // Execute query.
           List<Employee> employees = query.getResultList();

           for (Employee emp : employees) {
               System.out.println("Emp: " + emp.getEmpNo() + " : "
                       + emp.getEmpName());
           }
 
           // Commit data.
           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           // Rollback in case of an error occurred.
           session.getTransaction().rollback();
       }
   }
   
}
Results of running the example:

Demo2:

QueryObjectDemo2.java
package org.o7planning.tutorial.hibernate.query;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class QueryObjectDemo2 {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {

            // All the action with DB via Hibernate
            // must be located in one transaction
            // Start Transaction.                
            session.getTransaction().begin();
            
            // Create an HQL statement, query the object.
            // HQL with parameters.            
            // Equivalent to the SQL statement:
            // Select e.* from EMPLOYEE e cross join DEPARTMENT d
            // where e.DEPT_ID = d.DEPT_ID and d.DEPT_NO = :deptNo;        
            String sql = "Select e from " + Employee.class.getName() + " e "
                    + " where e.department.deptNo=:deptNo ";
 
            // Create query object.
            Query<Employee> query = session.createQuery(sql);

            query.setParameter("deptNo", "D10");

 
            // Execute query.
            List<Employee> employees = query.getResultList();

            for (Employee emp : employees) {
                System.out.println("Emp: " + emp.getEmpNo() + " : "
                        + emp.getEmpName());
            }
 
            // Commit data
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }
    }
}

8.2- Query a few columns using HQL

QuerySomeColumnDemo.java
package org.o7planning.tutorial.hibernate.query;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class QuerySomeColumnDemo {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {
            session.getTransaction().begin();
 
            // Query some columns.
            String sql = "Select e.empId, e.empNo, e.empName from "
                    + Employee.class.getName() + " e ";

            Query<Object[]> query = session.createQuery(sql);
 
            // Execute Query.
            // Get the array of Object
            List<Object[]> datas = query.getResultList();

            for (Object[] emp : datas) {
                System.out.println("Emp Id: " + emp[0]);
                System.out.println(" Emp No: " + emp[1]);
                System.out.println(" Emp Name: " + emp[2]);
            }
 
            // Commit data.
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }
 
    }
}
 
Results of running the example:

8.3- Query a few columns using HQL & JavaBean

In the case, if you need to extract the data in some columns of some tables, the best way will be to use Java beans. Class Java bean will have a constructor helping set up values in its different fields. This constructor participates in HQL query.
ShortEmpInfo.java
package org.o7planning.tutorial.hibernate.beans;

public class ShortEmpInfo {

    private Long empId;
    private String empNo;
    private String empName;

    //
    // Constructor have 3 parameters, will be used in the Hibernate Query.
    //
    public ShortEmpInfo(Long empId, String empNo, String empName) {
        this.empId = empId;
        this.empNo = empNo;
        this.empName = empName;
    }

    public Long getEmpId() {
        return empId;
    }

    public void setEmpId(Long empId) {
        this.empId = empId;
    }

    public String getEmpNo() {
        return empNo;
    }

    public void setEmpNo(String empNo) {
        this.empNo = empNo;
    }

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

}
ShortEmpInfoQueryDemo.java
package org.o7planning.tutorial.hibernate.query;

import java.util.List;

import org.hibernate.query.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.beans.ShortEmpInfo;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class ShortEmpInfoQueryDemo {

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {
            session.getTransaction().begin();
 
            // Using constructor of ShortEmpInfo
            String sql = "Select new " + ShortEmpInfo.class.getName()
                    + "(e.empId, e.empNo, e.empName)" + " from "
                    + Employee.class.getName() + " e ";

            Query<ShortEmpInfo> query = session.createQuery(sql);
 
            
            // Execute query.
            // Get a List of ShortEmpInfo
            List<ShortEmpInfo> employees = query.getResultList();

            for (ShortEmpInfo emp : employees) {
                System.out.println("Emp: " + emp.getEmpNo() + " : "
                        + emp.getEmpName());
            }
 
            // Commit data.
            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            // Rollback in case of an error occurred.
            session.getTransaction().rollback();
        }
    }
    
}

8.4- Query retrieves unique result

UniqueResultDemo.java
package org.o7planning.tutorial.hibernate.query;

import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.query.Query;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Department;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class UniqueResultDemo {

    public static Department getDepartment(Session session, String deptNo) {
        String sql = "Select d from " + Department.class.getName() + " d "//
                + " where d.deptNo= :deptNo ";
        Query<Department> query = session.createQuery(sql);
        query.setParameter("deptNo", deptNo);
        return (Department) query.getSingleResult();
    }

    public static Employee getEmployee(Session session, Long empId) {
        String sql = "Select e from " + Employee.class.getName() + " e "//
                + " where e.empId= :empId ";
        Query<Employee> query = session.createQuery(sql);
        query.setParameter("empId", empId);
        return (Employee) query.getSingleResult();
    }

    public static void main(String[] args) {
        SessionFactory factory = HibernateUtils.getSessionFactory();

        Session session = factory.getCurrentSession();

        try {
            session.getTransaction().begin();

            Department dept = getDepartment(session, "D10");
            Set<Employee> emps = dept.getEmployees();

            System.out.println("Dept Name: " + dept.getDeptName());
            for (Employee emp : emps) {
                System.out.println(" Emp name: " + emp.getEmpName());
            }

            Employee emp = getEmployee(session, 7839L);
            System.out.println("Emp Name: " + emp.getEmpName());

            session.getTransaction().commit();
        } catch (Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }
    }
    
}

9- Transient, Persistent and Detached

DataUtils.java
package org.o7planning.tutorial.hibernate;

import org.hibernate.Session;
import org.hibernate.query.Query;
import org.o7planning.tutorial.hibernate.entities.Department;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class DataUtils {

   public static Department findDepartment(Session session, String deptNo) {
       String sql = "Select d from " + Department.class.getName() + " d "//
               + " Where d.deptNo = :deptNo";
       Query<Department> query = session.createQuery(sql);
       query.setParameter("deptNo", deptNo);
       return query.getSingleResult();
   }

   public static Long getMaxEmpId(Session session) {
       String sql = "Select max(e.empId) from " + Employee.class.getName() + " e ";
       Query<Number> query = session.createQuery(sql);
       Number value = query.getSingleResult();
       if (value == null) {
           return 0L;
       }
       return value.longValue();
   }

   public static Employee findEmployee(Session session, String empNo) {
       String sql = "Select e from " + Employee.class.getName() + " e "//
               + " Where e.empNo = :empNo";
       Query<Employee> query = session.createQuery(sql);
       query.setParameter("empNo", empNo);
       return query.getSingleResult();
   }

}
This is a simple example using Session.persist (Object) to insert  Transient object into the DB.
The concept of object Transitent, Persistent, Detached will be explained in this example.
PersistDemo.java
package org.o7planning.tutorial.hibernate.demo;

import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Department;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class PersistDemo {

   public static void main(String[] args) {
       
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Department department = null;
       Employee emp = null;
       try {
           session.getTransaction().begin();

           Long maxEmpId = DataUtils.getMaxEmpId(session);
           Long empId = maxEmpId + 1;
           
           // Get Persistent object.
           department = DataUtils.findDepartment(session, "D10");
           
           // Create transient object
           emp = new Employee();
           emp.setEmpId(empId);
           emp.setEmpNo("E" + empId);
           emp.setEmpName("Name " + empId);
           emp.setJob("Coder");
           emp.setSalary(1000f);
           emp.setManager(null);
           emp.setHideDate(new Date());
           emp.setDepartment(department);
           
           // Using persist(..)
           // Now 'emp' is managed by Hibernate.
           // it has Persistent status.
           // No action at this time with DB.
           session.persist(emp);

           
           // At this step the data is pushed to the DB.
           // Execute Insert statement.
           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }

       // After the session is closed (commit, rollback, close)
       // Objects 'emp', 'dept' became the Detached objects.
       // It is no longer in the control of the session.        
       System.out.println("Emp No: " + emp.getEmpNo());
       
   }
   
}
Results of running the example:

10- Hibernate Lifecycle

Class Session of Hibernate possess some important methods that are divided into groups as the following illustration:
An object in Hibernate exist in one of four states:
  • Transient
  • Persistent
  • Removed
  • Detached
We explain them in the following illustrations:
  1. You create a new Java object from a Entity and that object is in the state of Transient. Hibernate does not know about its existence since it is independent from the management of Hibernate.
  2. If you get the Entity object with method get, load or find, you will get an object equivalent to 1 record in database. This object is in the state of Persistent. It is managed by Hibernate.
  3. Session calls one of the methods: save, saveOrUpdate, and persist. Merge puts the Transient object under the management of Hibernate and this object turns to the state of Persistent. In specific situations, it many insert or update data in DB.
  4. Session calls evict(..) or clear() in order to dismiss objects in the state of persistent from the management of Hibernate, and these objects are in a new state of Detached.
  5. Use update(..), saveOrUpdate(..), merge(..) will help reattach the Detached objects. In specific situations, it will create update or insert orders in DB. Objects turn back the state of Persistent.
  6. Session calls methods: remove(..), delete(..) to erase a record. Persistent object 

11- Insert,Update, Delete with Hibernate

11.1- Persistent

PersistentDemo.java
package org.o7planning.tutorial.hibernate.demo;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Department;

public class PersistentDemo {

   public static void main(String[] args) {
       
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Department department = null;

       try {
           session.getTransaction().begin();

           System.out.println("- Finding Department deptNo = D10...");
      
           // Persistent object.
           department = DataUtils.findDepartment(session, "D10");

           System.out.println("- First change Location");
     
           
           // Changing something on Persistent object.
           department.setLocation("Chicago " + System.currentTimeMillis());
           
           System.out.println("- Location = " + department.getLocation());

           System.out.println("- Calling flush...");
   
           // Use session.flush () to actively push the changes to the DB.
           // It works for all changed Persistent objects.
           session.flush();

           System.out.println("- Flush OK");

           System.out.println("- Second change Location");
           
           // Change something on Persistent object
           department.setLocation("Chicago " + System.currentTimeMillis());
 
           // Print out location
           System.out.println("- Location = " + department.getLocation());

           System.out.println("- Calling commit...");
 
           // Commit
           session.getTransaction().commit();

           System.out.println("- Commit OK");
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
 
       // Create the session after it had been closed earlier
       // (Cause by commit or update)
       session = factory.getCurrentSession();
       try {
           session.getTransaction().begin();

           System.out.println("- Finding Department deptNo = D10...");
           
           // Query lại Department D10.
           
           department = DataUtils.findDepartment(session, "D10");
 
           // Print out location
           System.out.println("- D10 Location = " + department.getLocation());

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
   
}
Results of running the example:

11.2- Transient --> Persistent : Overview

11.3- Transient --> Persistent : Using persist(Object)

PersistTransientDemo.java
package org.o7planning.tutorial.hibernate.demo;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;
import org.o7planning.tutorial.hibernate.entities.Timekeeper;

public class PersistTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper persist_Transient(Session session, Employee emp) {
 
       // Note:
       // Configuring of timekeeperId
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")            
       Timekeeper tk1 = new Timekeeper();

       tk1.setEmployee(emp);
       tk1.setInOut(Timekeeper.IN);
       tk1.setDateTime(new Date());
  
       // Now, 'tk1' is transient object
       System.out.println("- tk1 Persistent? " + session.contains(tk1));

       System.out.println("====== CALL persist(tk).... ===========");
 
       
       // Hibernate assign value to Id of 'tk1'
       // No action to DB.
       session.persist(tk1);
 
       System.out
               .println("- tk1.getTimekeeperId() = " + tk1.getTimekeeperId());
 
       
       // Now 'tk1' is Persistent object.
       // But no action with DB.
       // ==> true
       System.out.println("- tk1 Persistent? " + session.contains(tk1));

       System.out.println("- Call flush..");
 
       
       // Flush data to DB.
       // Hibernate execute insert statement.
       session.flush();

       String timekeeperId = tk1.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk1.getInOut());
       System.out.println("- dateTime = " + df.format(tk1.getDateTime()));
       System.out.println();
       return tk1;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           persist_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
   
}
Results of running the example:

11.4- Transient --> Persistent : Using save(Object)

SaveTransientDemo.java
package org.o7planning.tutorial.hibernate.demo;

import java.io.Serializable;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;
import org.o7planning.tutorial.hibernate.entities.Timekeeper;

public class SaveTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper persist_Transient(Session session, Employee emp) {
     
       // See configuration of timekeeperId:
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")
       // Create an Object, Transitent state.        
       Timekeeper tk2 = new Timekeeper();

       tk2.setEmployee(emp);
       tk2.setInOut(Timekeeper.IN);
       tk2.setDateTime(new Date());

       // Now 'tk3' are state Transient.        
       System.out.println("- tk2 Persistent? " + session.contains(tk2));

       System.out.println("====== CALL save(tk).... ===========");

       // save() very similar to persist()
       // save() return ID, persist() return void.
       // Hibernate assign ID value to 'tk2', no action with DB
       // And return ID of 'tk2'.        
       Serializable id = session.save(tk2);

       System.out.println("- id = " + id);

       //
       System.out
               .println("- tk2.getTimekeeperId() = " + tk2.getTimekeeperId());

     
       // Now, 'tk2' has Persistent state
       // It has been managed in Session.
       // ==> true
       System.out.println("- tk2 Persistent? " + session.contains(tk2));

       System.out.println("- Call flush..");

       // To push data into the DB, call flush().
       // If not call flush() data will be pushed to the DB when calling commit().
       // Will execute insert statement.
       session.flush();

       String timekeeperId = tk2.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk2.getInOut());
       System.out.println("- dateTime = " + df.format(tk2.getDateTime()));
       System.out.println();
       return tk2;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           persist_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}
Results of running the example:

11.5- Transient --> Persistent : Using saveOrUpdate(Object)

SaveOrUpdateTransientDemo.java
package org.o7planning.tutorial.hibernate.demo;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;
import org.o7planning.tutorial.hibernate.entities.Timekeeper;

public class SaveOrUpdateTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper saveOrUpdate_Transient(Session session,
           Employee emp) {

       // See configuration of timekeeperId:
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")
       // Create an Object, Transitent state.
       Timekeeper tk3 = new Timekeeper();

       tk3.setEmployee(emp);
       tk3.setInOut(Timekeeper.IN);
       tk3.setDateTime(new Date());

       // Now 'tk3' are state Transient.
       System.out.println("- tk3 Persistent? " + session.contains(tk3));

       System.out.println("====== CALL saveOrUpdate(tk).... ===========");

       // Here Hibernate checks, 'tk3' have ID or not (timekeeperId)
       // If no, it will be assigned automatically
       session.saveOrUpdate(tk3);

       System.out
               .println("- tk3.getTimekeeperId() = " + tk3.getTimekeeperId());

       // Now 'tk3' has Persistent state
       // It has been managed in Session.
       // But no action insert, or update to DB.
       // ==> true
       System.out.println("- tk3 Persistent? " + session.contains(tk3));

       System.out.println("- Call flush..");

       // To push data into the DB, call flush().
       // If not call flush() data will be pushed to the DB when calling commit().
       // Now possible to Insert or Update DB. (!!!)
       // Depending on the ID of 'tk3' exists in the DB or not
       session.flush();

       String timekeeperId = tk3.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk3.getInOut());
       System.out.println("- dateTime = " + df.format(tk3.getDateTime()));
       System.out.println();
       return tk3;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           saveOrUpdate_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}
Results of running the example:

11.6- Transient --> Persistent : Using merge(Object)

MergeTransientDemo.java
package org.o7planning.tutorial.hibernate.demo;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;
import org.o7planning.tutorial.hibernate.entities.Timekeeper;

public class MergeTransientDemo {

   private static DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");

   private static Timekeeper saveOrUpdate_Transient(Session session,
           Employee emp) {
     
       // Note:
       // Configuring of timekeeperId
       // @GeneratedValue(generator = "uuid")
       // @GenericGenerator(name = "uuid", strategy = "uuid2")        
       Timekeeper tk4 = new Timekeeper();

       tk4.setEmployee(emp);
       tk4.setInOut(Timekeeper.IN);
       tk4.setDateTime(new Date());

       // Now 'tk4' Transient status.
       System.out.println("- tk4 Persistent? " + session.contains(tk4));

       System.out.println("====== CALL merge(tk).... ===========");

 
       // Hibernate2 has method saveOrUpdateCopy
       // Hibernate3 change saveOrUpdateCopy to merge
       // So there will be similarities between the two methods merge and copyOrUpdate
       // Here Hibernate check tk4 has ID or not
       // If not, Hibernate assign value to ID of tk4
       // Return copy of tk4.
       Timekeeper tk4Copy = (Timekeeper) session.merge(tk4);

       System.out
               .println("- tk4.getTimekeeperId() = " + tk4.getTimekeeperId());

   
       // Now 'tk4' still Transient state.
       // and 'tk4Copy' has Persistent status
       // No action with DB (insert or update).
       System.out.println("- tk4 Persistent? " + session.contains(tk4));

       // 'tk4Copy' has Persistent status
       // ==> true
       System.out
               .println("- tk4Copy Persistent? " + session.contains(tk4Copy));

       System.out.println("- Call flush..");
       
     
       // This time have Insert or Update to DB. (!!!)
       session.flush();

       // 'tk4' still Transitent, after flush().
       // merge(..) safer than saveOrUpdate().
       System.out.println("- tk4 Persistent? " + session.contains(tk4));

       //
       String timekeeperId = tk4.getTimekeeperId();
       System.out.println("- timekeeperId = " + timekeeperId);
       System.out.println("- inOut = " + tk4.getInOut());
       System.out.println("- dateTime = " + df.format(tk4.getDateTime()));
       System.out.println();
       return tk4;
   }

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           emp = DataUtils.findEmployee(session, "E7499");

           saveOrUpdate_Transient(session, emp);

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}
Results of running the example:

11.7- Persistent --> Detached

An object in a Persistent condition managed by Hibernate can be turned to the state of Detached (be independent from the management of Hibernate) through the method of Session:
  • evict (Object)
    • Remove an object from the management of Hibernate
  • clear()
    • Remove all objects managed by Hibernate.
Of course, when a session order commit(), close() or rollback(), the current session has finished. All Persistence objects of this session will be Detached from a newly-opened session.
EvictDemo.java
package org.o7planning.tutorial.hibernate.demo;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class EvictDemo {

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       try {
           session.getTransaction().begin();

           // This is object has Persistent status
           emp = DataUtils.findEmployee(session, "E7499");

           // ==> true
           System.out.println("- emp Persistent? " + session.contains(emp));

     
           // using evict() to evicts a single object from the session
           session.evict(emp);

           // Now 'emp' has Detached status
           // ==> false
           System.out.println("- emp Persistent? " + session.contains(emp));

       
           // All change on the 'emp' will not update
           // if not reatach 'emp' to session
           emp.setEmpNo("NEW");

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}
Results of running the example:
ClearDemo.java
package org.o7planning.tutorial.hibernate.demo;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Department;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class ClearDemo {
   
   
   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session = factory.getCurrentSession();
       Employee emp = null;
       Department dept = null;
       try {
           session.getTransaction().begin();

           // It is an object has Persistent status.
           emp = DataUtils.findEmployee(session, "E7499");
           dept = DataUtils.findDepartment(session, "D10");

       
           // clear() evicts all the objects in the session.
           session.clear();


           // Now 'emp' & 'dept' has Detached status
           // ==> false
           System.out.println("- emp Persistent? " + session.contains(emp));
           System.out.println("- dept Persistent? " + session.contains(dept));

           // All change on the 'emp' will not update
           // if not reatach 'emp' to session
           emp.setEmpNo("NEW");

           dept = DataUtils.findDepartment(session, "D20");
           System.out.println("Dept Name = "+ dept.getDeptName());

           session.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session.getTransaction().rollback();
       }
   }
}
Results of running the example:

11.8- Detached --> Persistent : Overview

An object detached from the management of Hibernate can be re-attached through some methods of Session:...
  • update(Object)
  • saveOrUpdate(Object)
  • merge(Object)
  • refresh(Object)
  • lock(Object)
You can see the difference among methods in the following examples:

11.9- Detached --> Persistent : Using update(Object)

UpdateDetachedDemo.java
package org.o7planning.tutorial.hibernate.demo;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class UpdateDetachedDemo {

   public static void main(String[] args) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session1 = factory.getCurrentSession();
       Employee emp = null;
       try {
           session1.getTransaction().begin();

           // This is a Persistent object.
           emp = DataUtils.findEmployee(session1, "E7499");

           // session1 was closed after a commit is called.
           session1.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session1.getTransaction().rollback();
       }

       // Open other session
       Session session2 = factory.getCurrentSession();

       try {
           session2.getTransaction().begin();

       
           // Check state of 'emp'
           // ==> false
           System.out.println("- emp Persistent? " + session2.contains(emp));

           System.out.println("Emp salary: " + emp.getSalary());

           emp.setSalary(emp.getSalary() + 100);

         
           // update (..) is only used for Detached object.
           // (Not for Transient object).
           // Use the update (emp) to bring back emp Persistent state.            
           session2.update(emp);
         
           // Call flush
           // Update statement will be called.
           session2.flush();

           System.out.println("Emp salary after update: " + emp.getSalary());

           // session2 was closed after a commit is called.
           session2.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session2.getTransaction().rollback();
       }

   }
}
Results of running the example:

11.10- Detached --> Persistent : Using saveOrUpdate(Object)

SaveOrUpdateDetachedDemo.java
package org.o7planning.tutorial.hibernate.demo;

import java.util.Random;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class SaveOrUpdateDetachedDemo {

   public static void main(String[] args) {

       // An object Detached state.
       Employee emp = getEmployee_Detached();

       System.out.println(" - GET EMP " + emp.getEmpId());

       // Random delete or not delete Employee
       boolean delete = deleteOrNotDelete(emp.getEmpId());

       System.out.println(" - DELETE? " + delete);

       // Call saveOrUpdate for detached object.
       saveOrUpdate_test(emp);
     
       // After call saveOrUpdate()
       System.out.println(" - EMP ID " + emp.getEmpId());
   }

   
   // Return Employee object has Detached state
   private static Employee getEmployee_Detached() {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session1 = factory.getCurrentSession();
       Employee emp = null;
       try {
           session1.getTransaction().begin();

           Long maxEmpId = DataUtils.getMaxEmpId(session1);
           System.out.println(" - Max Emp ID " + maxEmpId);

           Employee emp2 = DataUtils.findEmployee(session1, "E7839");

           Long empId = maxEmpId + 1;
           emp = new Employee();
           emp.setEmpId(empId);
           emp.setEmpNo("E" + empId);

           emp.setDepartment(emp2.getDepartment());
           emp.setEmpName(emp2.getEmpName());

           emp.setHideDate(emp2.getHideDate());
           emp.setJob("Test");
           emp.setSalary(1000F);

           // emp has been managed by Hibernate
           session1.persist(emp);

           // session1 was closed after a commit is called.
           // An Employee record are insert into DB.            
           session1.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session1.getTransaction().rollback();
       }
       // Session1 closed 'emp' switch to Detached state.
       return emp;
   }

   // Random: delete or not delete.
   private static boolean deleteOrNotDelete(Long empId) {
       // A random number 0-9
       int random = new Random().nextInt(10);
       if (random < 5) {
           return false;
       }
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session2 = factory.getCurrentSession();
       try {
           session2.getTransaction().begin();
           String sql = "Delete " + Employee.class.getName() + " e "
                   + " where e.empId =:empId ";
           Query query = session2.createQuery(sql);
           query.setParameter("empId", empId);

           query.executeUpdate();

           session2.getTransaction().commit();
           return true;
       } catch (Exception e) {
           e.printStackTrace();
           session2.getTransaction().rollback();
           return false;
       }
   }

   private static void saveOrUpdate_test(Employee emp) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       // Open other session
       Session session3 = factory.getCurrentSession();

       try {
           session3.getTransaction().begin();

           // Check state of emp
           // ==> false
           System.out.println(" - emp Persistent? " + session3.contains(emp));

           System.out.println(" - Emp salary before update: "
                   + emp.getSalary());
         
           // Set new salary for Detached emp object.
           emp.setSalary(emp.getSalary() + 100);

         
           // Using saveOrUpdate(emp) to switch emp to Persistent state
           // Note: If exists object same ID in session, this method raise Exception
           //
           // Now, no action with DB.            
           session3.saveOrUpdate(emp);
         
           // By pushing data into the DB.
           // It will call a Insert or update statement.
           // If the record is deleted before ==> insert
           // Else ==> update.    
           session3.flush();

           System.out
                   .println(" - Emp salary after update: " + emp.getSalary());

           // session3 was closed after a commit is called.
           session3.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session3.getTransaction().rollback();
       }

   }

}
Running the examples on a few times, you can see two situations, saveOrUpdate call Insert or Update on DB.
INSERT:
UPDATE:

11.11- Detached --> Persistent : Using merge(Object)

Hibernate version 2 has  saveOrUpdateCopy(Object) method. From the version 3 onwards, it is renamed merge(Object). Thus, merge has some similarity and difference compared with  saveOrUpdate.

merge(Object) does not put objects under the management of Hibernate, but it create a copy of the object and manage the copy object instead.

If you call saveOrUpdate(aObject) while bObject is being managed by Hibernate and has the same ID with aObject, an exception will be thrown out, when you use the  merge(aObject) not get this Exception.
MergeDetachedDemo.java
package org.o7planning.tutorial.hibernate.demo;

import java.util.Random;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class MergeDetachedDemo {

   public static void main(String[] args) {

       // An object has Detached status
       Employee emp = getEmployee_Detached();

       System.out.println(" - GET EMP " + emp.getEmpId());

       // Random: delete or not delete the Employee by ID.
       boolean delete = deleteOrNotDelete(emp.getEmpId());

       System.out.println(" - DELETE? " + delete);

       // Call saveOrUpdate Detached object
       saveOrUpdate_test(emp);

       // After call saveOrUpdate
       // ...
       System.out.println(" - EMP ID " + emp.getEmpId());
   }

 
   // Method return Employee object
   // and has Detached status.
   private static Employee getEmployee_Detached() {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session1 = factory.getCurrentSession();
       Employee emp = null;
       try {
           session1.getTransaction().begin();

           Long maxEmpId = DataUtils.getMaxEmpId(session1);
           System.out.println(" - Max Emp ID " + maxEmpId);

           Employee emp2 = DataUtils.findEmployee(session1, "E7839");

           Long empId = maxEmpId + 1;
           emp = new Employee();
           emp.setEmpId(empId);
           emp.setEmpNo("E" + empId);

           emp.setDepartment(emp2.getDepartment());
           emp.setEmpName(emp2.getEmpName());

           emp.setHideDate(emp2.getHideDate());
           emp.setJob("Test");
           emp.setSalary(1000F);

           // 'emp' has Persistant state
           session1.persist(emp);

       
           // session1 was closed after a commit is called.
           // An Employee record are insert into DB.
           session1.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session1.getTransaction().rollback();
       }
       // session1 closed, 'emp' switched Detached state.
       return emp;
   }

 
   // Delete Employee by ID
   // Random: delete or not delete
   private static boolean deleteOrNotDelete(Long empId) {
       // A random number 0-9
       int random = new Random().nextInt(10);
       if (random < 5) {
           return false;
       }
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session2 = factory.getCurrentSession();
       try {
           session2.getTransaction().begin();
           String sql = "Delete " + Employee.class.getName() + " e "
                   + " where e.empId =:empId ";
           Query query = session2.createQuery(sql);
           query.setParameter("empId", empId);

           query.executeUpdate();

           session2.getTransaction().commit();
           return true;
       } catch (Exception e) {
           e.printStackTrace();
           session2.getTransaction().rollback();
           return false;
       }
   }

   private static void saveOrUpdate_test(Employee emp) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       // Open other session
       Session session3 = factory.getCurrentSession();

       try {
           session3.getTransaction().begin();

       
           // The fact, 'emp' has Detached state
           // It is not managed by Hibernate.
           // Check the status of emp:
           // ==> false
           System.out.println(" - emp Persistent? " + session3.contains(emp));

           System.out.println(" - Emp salary before update: "
                   + emp.getSalary());

           // Set new salary for Detached object 'emp'
           emp.setSalary(emp.getSalary() + 100);

       
           // merge(emp) return empMerge, a copy of 'emp',
           // empMerge managed by Hibernate
           // 'emp' still in Detached state
           //
           // At this time there is no action regarding DB.
           Employee empMerge = (Employee) session3.merge(emp);

           // ==> false
           System.out.println(" - emp Persistent? " + session3.contains(emp));
           // ==> true
           System.out.println(" - empMerge Persistent? "
                   + session3.contains(empMerge));

         
           // Push data into the DB.
           // Here it is possible to create the Insert or Update on DB.
           // If the corresponding record has been deleted by someone, it insert
           // else it update
           session3.flush();

           System.out
                   .println(" - Emp salary after update: " + emp.getSalary());

           // session3 closed after a commit is called.
           session3.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session3.getTransaction().rollback();
       }

   }

}
Results of running the example:
INSERT:
UPDATE:

11.12- Detached --> Persistent : Using refresh(Object)

RefreshDetachedDemo.java
package org.o7planning.tutorial.hibernate.demo;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.tutorial.hibernate.DataUtils;
import org.o7planning.tutorial.hibernate.HibernateUtils;
import org.o7planning.tutorial.hibernate.entities.Employee;

public class RefreshDetachedDemo {

   public static void main(String[] args) {

       // an Object with Detached status
       Employee emp = getEmployee_Detached();

       System.out.println(" - GET EMP " + emp.getEmpId());

       // Refresh Object  
       refresh_test(emp);
   }

 
   // Return Employee object has Detached state
   private static Employee getEmployee_Detached() {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       Session session1 = factory.getCurrentSession();
       Employee emp = null;
       try {
           session1.getTransaction().begin();

           emp = DataUtils.findEmployee(session1, "E7839");

           // session1 was closed after a commit is called.
           // An Employee record are insert into DB.
           session1.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session1.getTransaction().rollback();
       }
       // Session1 closed 'emp' switch to Detached state.
       return emp;
   }

   private static void refresh_test(Employee emp) {
       SessionFactory factory = HibernateUtils.getSessionFactory();

       // Open other session
       Session session2 = factory.getCurrentSession();

       try {
           session2.getTransaction().begin();

       
           // Check the status of 'emp' (Detached)
           // ==> false
           System.out.println(" - emp Persistent? " + session2.contains(emp));

           System.out.println(" - Emp salary before update: "
                   + emp.getSalary());

            // Set new salary for 'emp'.
           emp.setSalary(emp.getSalary() + 100);

         
           // refresh: make a query statement
           // and switch 'emp' to Persistent state
           // The changes are ignored
           session2.refresh(emp);

           // ==> true
           System.out.println(" - emp Persistent? " + session2.contains(emp));

           System.out.println(" - Emp salary after refresh: "
                   + emp.getSalary());
           
           session2.getTransaction().commit();
       } catch (Exception e) {
           e.printStackTrace();
           session2.getTransaction().rollback();
       }

   }

}
Results of running the example:

11.13- Detached --> Persistent : Using lock(Object)

  • TODO...

12- Generate database from Entities ***

Hibernate allows you to create tables from Entity with a full of constraints among tables.