Working with MySQL Database using C#

1- Introduction

Trong tài liệu này tôi sẽ hướng dẫn bạn thao tác với MySQL Database từ C#, mục tiêu bao gồm:
  1. Query
  2. Insert
  3. Update
  4. Delete
  5. Gọi hàm, thủ tục từ C#,...
Tài liệu sử dụng SIMPLEHR, một Database Schema ví dụ được sử dụng trong nhiều hướng dẫn trên o7planning.org, bạn có thể tạo Schema này trên Oracle, MySQL hoặc SQL Server. Bạn có thể xem hướng dẫn tại:

2- Connect to MySQL Database with C#

Create project CsMySQLTutorial:
Project is created.
You need to declare the libraries, and need a utility class ( DBUtils.cs) which help to connect to the database. With SQL Server database, you can see the instructions at:
DBMySQLUtils.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;

namespace Tutorial.SqlConn
{
   class DBMySQLUtils
   {

       public static MySqlConnection
                GetDBConnection(string host, int port, string database, string username, string password)
       {
           // Connection String.
           String connString = "Server=" + host + ";Database=" + database
               + ";port=" + port + ";User Id=" + username + ";password=" + password;

           MySqlConnection conn = new MySqlConnection(connString);

           return conn;
       }
     
   }
}
DBUtils.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;

namespace Tutorial.SqlConn
{
   class DBUtils
   {
       public static MySqlConnection GetDBConnection()
       {
           string host = "192.168.205.130";
           int port = 3306;
           string database = "simplehr";
           string username = "root";
           string password = "1234";

           return DBMySQLUtils.GetDBConnection(host, port, database, username, password);
       }
     
   }
}

3- MySqlCommand

Trong C# để thao tác với MySQL Database, chẳng hạn query, insert, update, delete bạn sử dụng một đối tượng MySqlCommand, MySqlCommand là một class mở rộng từ DbCommand. Trong trường hợp bạn cần query, insert,update hoặc delete trong Oracle Database bạn cần sử dụng OracleCommand, hoặc với SQL ServerSqlCommand. Thật đáng tiếc là bạn sẽ rất khó khăn nếu muốn sử dụng một mã nguồn cho các Database khác nhau.
Bạn có thể tạo đối tượng MySqlCommand để thao tác với MySQL Database:
MySqlConnection conn = DBUtils.GetDBConnection();

// Way 1:

// Create a command associated with the Connection.
MySqlCommand cmd = conn.CreateCommand();

// Set Command Text
cmd.CommandText = sql;

// Way 2 :

// Create a Command
MySqlCommand cmd = new MySqlCommand(sql);

// Set connection for command.
cmd.Connection = conn;


// Way 3:

// Create a command associated with the Connection.

MySqlCommand cmd = new MySqlCommand(sql, conn);

4- Query

Ví dụ truy vấn dữ liệu sử dụng C#.
QueryDataExample.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Tutorial.SqlConn;
using System.Data.Common;
using MySql.Data.MySqlClient;

namespace CsMySQLTutorial
{
  class QueryDataExample
  {
      static void Main(string[] args)
      {
          // Get connection.
          MySqlConnection conn = DBUtils.GetDBConnection();
          conn.Open();
          try
          {
              QueryEmployee(conn);
          }
          catch (Exception e)
          {
              Console.WriteLine("Error: " + e);
              Console.WriteLine(e.StackTrace);
          }
          finally
          {
              // Close connection.
              conn.Close();
              // Freeing Resources.
              conn.Dispose();
          }      
          Console.Read();
      }

      private static void QueryEmployee(MySqlConnection conn)
      {
          string sql = "Select Emp_Id, Emp_No, Emp_Name, Mng_Id from Employee";

          // Create command.
          // Tạo một đối tượng Command.
          MySqlCommand cmd = new MySqlCommand();

          // Set connection for command.
          cmd.Connection = conn;
          cmd.CommandText = sql;

         
          using (DbDataReader reader = cmd.ExecuteReader())
          {
              if (reader.HasRows)
              {
                 
                  while (reader.Read())
                  {
                      // Get index of Column Emp_ID in query statement.
                      int empIdIndex = reader.GetOrdinal("Emp_Id"); // 0
                     

                      long empId =  Convert.ToInt64(reader.GetValue(0));
                     
                      // Index of Emp_ID = 1
                      string empNo = reader.GetString(1);
                      int empNameIndex = reader.GetOrdinal("Emp_Name");// 2
                      string empName = reader.GetString(empNameIndex);

                      // Index of column Mng_Id.
                      int mngIdIndex = reader.GetOrdinal("Mng_Id");

                      long? mngId = null;

                      // If a column is nullable always check for DBNull...
                      if (!reader.IsDBNull(mngIdIndex))
                      {
                          mngId = Convert.ToInt64(reader.GetValue(mngIdIndex));
                      }
                      Console.WriteLine("--------------------");
                      Console.WriteLine("empIdIndex:" + empIdIndex);
                      Console.WriteLine("EmpId:" + empId);
                      Console.WriteLine("EmpNo:" + empNo);
                      Console.WriteLine("EmpName:" + empName);
                      Console.WriteLine("MngId:" + mngId);
                  }
              }
          }

      }
  }

}
Running the example:
Node: The reason for the "using" statement is to ensure that the object is disposed as soon as it goes out of scope, and it doesn't require explicit code to ensure that this happens.
// Sử dụng using với các đối tượng kiểu IDispose.
// (Là đối tượng của Interface IDispose).

using (DbDataReader reader = cmd.ExecuteReader())
{
   // Code sử dụng reader
}


// Tương đương với viết một cách trực quan:

DbDataReader reader = cmd.ExecuteReader();
try
{
   // Code sử dụng reader
}
finally
{
    // Gọi phương thức tiêu hủy đối tượng
    // Giải phóng tài nguyên.
    reader.Dispose();
}

5- Insert

Ví dụ sau insert thêm một bản ghi vào bảng Salary_Grade.
InsertDataExample.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Tutorial.SqlConn;
using System.Data.Common;
using System.Data;
using MySql.Data.MySqlClient;

namespace CsMySQLTutorial
{
   class InsertDataExample
   {
         static void Main(string[] args)
         {

           // Get Connection
           MySqlConnection connection = DBUtils.GetDBConnection();
           connection.Open();
           try
           {    
               // Insert statement.
               string sql = "Insert into Salary_Grade (Grade, High_Salary, Low_Salary) "
                                                + " values (@grade, @highSalary, @lowSalary) ";

               MySqlCommand cmd = connection.CreateCommand();
               cmd.CommandText = sql;  

               // Create Parameter.
               MySqlParameter gradeParam = new MySqlParameter("@grade",SqlDbType.Int);
               gradeParam.Value = 3;
               cmd.Parameters.Add(gradeParam);

               // Add parameter @highSalary (Write shorter)
               MySqlParameter highSalaryParam = cmd.Parameters.Add("@highSalary", SqlDbType.Float);
               highSalaryParam.Value = 20000;

               // Add parameter @lowSalary (more shorter).
               cmd.Parameters.Add("@lowSalary", SqlDbType.Float ).Value = 10000;

               // Execute (for Delete,Insert or Update).
               int rowCount = cmd.ExecuteNonQuery();

               Console.WriteLine("Row Count affected = " + rowCount);
           }
           catch (Exception e)
           {
               Console.WriteLine("Error: " + e);
               Console.WriteLine(e.StackTrace);
           }
           finally
           {
               // Close connection
               connection.Close();
               // Freeing Resources
               connection.Dispose();
               connection = null;
           }
         

           Console.Read();

        }
   }

}
Running the example:

6- Update

Ví dụ update trong C#.
UpdateExample.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;
using Tutorial.SqlConn;
using System.Data;

namespace CsMySQLTutorial
{
   class UpdateExample
   {
       static void Main(string[] args)
       {
           // Get connection.
           MySqlConnection conn  = DBUtils.GetDBConnection();
           conn.Open();
           try
           {
               string sql = "Update Employee set Salary = @salary where Emp_Id = @empId";

               // Create command.
               MySqlCommand cmd = new MySqlCommand();

               // Set connection for command.
               cmd.Connection = conn;
               // Set command text.
               cmd.CommandText = sql;

               // Add and set value for parameter.
               cmd.Parameters.Add("@salary", SqlDbType.Float).Value = 850;
               cmd.Parameters.Add("@empId", SqlDbType.Decimal).Value = 7369;

               // Execute (for Delete, Insert,Update).
               int rowCount = cmd.ExecuteNonQuery();

               Console.WriteLine("Row Count affected = " + rowCount);
           }
           catch (Exception e)
           {
               Console.WriteLine("Error: " + e);
               Console.WriteLine(e.StackTrace);
           }
           finally
           {
               // Close connection
               conn.Close();
               // Freeing resources.
               conn.Dispose();
               conn = null;
           }


           Console.Read();

       }
   }

}
Running the example:

7- Delete

Ví dụ sử dụng C# xóa dữ liệu trong SQL.
DeleteExample.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;
using Tutorial.SqlConn;
using System.Data;

namespace CsMySQLTutorial
{
   class DeleteExample
   {
       static void Main(string[] args)
       {
           // Get connection to database.
           MySqlConnection conn  = DBUtils.GetDBConnection();
           conn.Open();
           try
           {        

               string sql = "Delete from Salary_Grade where Grade = @grade ";

               // Create Command object.
               MySqlCommand cmd = new MySqlCommand();

               // Set Connection for command.
               cmd.Connection = conn;
               // Set Command Text.
               cmd.CommandText = sql;

               cmd.Parameters.Add("@grade", SqlDbType.Int).Value = 3;  

               // Execute (for Delete, insert, update).
               int rowCount = cmd.ExecuteNonQuery();

               Console.WriteLine("Row Count affected = " + rowCount);
           }
           catch (Exception e)
           {
               Console.WriteLine("Error: " + e);
               Console.WriteLine(e.StackTrace);
           }
           finally
           {
               // Close connection.
               conn.Close();
               // Freeing resources.
               conn.Dispose();
               conn = null;
           }


           Console.Read();

       }
   }

}

8- Call procedures in C#

Bạn cần tạo ra một thủ tục đơn giản trong MySQL và gọi nó trong C#:
Get_Employee_Info
-- This procedure retrieves information of an employee,
-- Input parameter: p_Emp_ID (Integer)
-- There are four output parameters v_Emp_No, v_First_Name, v_Last_Name, v_Hire_Date

CREATE PROCEDURE get_Employee_Info(p_Emp_ID     Integer,
                                 out       v_Emp_No        Varchar(50) ,
                                 out       v_First_Name    Varchar(50) ,
                                 Out       v_Last_name    Varchar(50) ,
                                 Out       v_Hire_date      Date)
BEGIN
set v_Emp_No  = concat( 'E' , Cast(p_Emp_Id as char(15)) );
--
set v_First_Name = 'Michael';
set v_Last_Name  = 'Smith';
set v_Hire_date  = curdate();
END
CallProcedureExample.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Tutorial.SqlConn;
using System.Data;
using MySql.Data.MySqlClient;

namespace CsMySQLTutorial
{
   class CallProcedureExample
   {
       static void Main(string[] args)
       {
           MySqlConnection conn = DBUtils.GetDBConnection();
           conn.Open();
           try
           {
               // Get_Employee_Info                
               // @p_Emp_Id       Integer ,
               // @v_Emp_No      Varchar(50)   OUTPUT
               // @v_First_Name  Varchar(50)   OUTPUT
               // @v_Last_Name  Varchar(50)    OUTPUT
               // @v_Hire_Date    Date         OUTPUT

               // Create a Command object to call procedure Get_Employee_Info
               MySqlCommand cmd = new MySqlCommand("Get_Employee_Info", conn);

               // Command Type is StoredProcedure
               cmd.CommandType = CommandType.StoredProcedure;

               // Add parameter @p_Emp_Id and set value = 100
               cmd.Parameters.Add("@p_Emp_Id", SqlDbType.Int).Value =100;

               // Add parameter @v_Emp_No type of Varchar(20).
               cmd.Parameters.Add(new MySqlParameter("@v_Emp_No", MySqlDbType.VarChar, 20));
               cmd.Parameters.Add(new MySqlParameter("@v_First_Name", MySqlDbType.VarChar, 50));
               cmd.Parameters.Add(new MySqlParameter("@v_Last_Name", MySqlDbType.VarChar, 50));
               cmd.Parameters.Add(new MySqlParameter("@v_Hire_Date", MySqlDbType.Date));

               // Register parameter @v_Emp_No is OUTPUT.
               cmd.Parameters["@v_Emp_No"].Direction = ParameterDirection.Output;
               cmd.Parameters["@v_First_Name"].Direction = ParameterDirection.Output;
               cmd.Parameters["@v_Last_Name"].Direction = ParameterDirection.Output;
               cmd.Parameters["@v_Hire_Date"].Direction = ParameterDirection.Output;

               // Execute procedure.
               cmd.ExecuteNonQuery();

               // Get output values.
               string empNo = cmd.Parameters["@v_Emp_No"].Value.ToString();
               string firstName = cmd.Parameters["@v_First_Name"].Value.ToString();
               string lastName = cmd.Parameters["@v_Last_Name"].Value.ToString();
               DateTime hireDate = (DateTime)cmd.Parameters["@v_Hire_Date"].Value;


               Console.WriteLine("Emp No: " + empNo);
               Console.WriteLine("First Name: " + firstName);
               Console.WriteLine("Last Name: " + lastName);
               Console.WriteLine("Hire Date: " + hireDate);

           }
           catch (Exception e)
           {
               Console.WriteLine("Error: " + e);
               Console.WriteLine(e.StackTrace);
           }
           finally
           {
               conn.Close();
               conn.Dispose();
           }

           Console.Read();
       }
   }


}
Running the example:

9- Call procedures in C#

Bạn cần một hàm đơn giản và gọi nó trong C#.
Get_Emp_No
DROP function  if Exists `Get_Emp_No`;
 
-- When programming the function / procedure you need to use semicolon
-- to separate the different commands.
-- Use DELIMITER $$ to allow use of semicolons.
DELIMITER $$
 


CREATE Function Get_Emp_No (p_Emp_Id  Integer) Returns Varchar(50)
Begin    
 
   return  concat('E', CAST(p_Emp_Id  as  char)) ;
   
END;
CallFunctionExample.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Tutorial.SqlConn;
using System.Data;
using MySql.Data.MySqlClient;


namespace CsMySQLTutorial
{
   class CallFunctionExample
   {
       static void Main(string[] args)
       {
           MySqlConnection conn = DBUtils.GetDBConnection();
           conn.Open();
           try
           {
               // Get_Emp_No                
               // @p_Emp_Id       Integer

               // Create a Command object to call Get_Emp_No function.
               MySqlCommand cmd = new MySqlCommand("Get_Emp_No", conn);

               // CommandType is StoredProcedure
               cmd.CommandType = CommandType.StoredProcedure;

               // Add parameter @p_Emp_Id and set value = 100.
               cmd.Parameters.AddWithValue("@p_Emp_Id", MySqlDbType.Int32).Value = 100;

               // Create result Parameter.
               MySqlParameter resultParam = new MySqlParameter("@Result", MySqlDbType.VarChar);            

               //  
               // Sét nó là kiểu trả về (ParameterDirection.ReturnValue)
               resultParam.Direction = ParameterDirection.ReturnValue;

               // Add to parameters
               cmd.Parameters.Add(resultParam);
               
               // Call function.
               cmd.ExecuteNonQuery();

               string empNo = null;
               if (resultParam.Value != DBNull.Value)
               {
                   empNo = (string)resultParam.Value;
               }                
               Console.WriteLine("Emp No: " + empNo);

           }
           catch (Exception e)
           {
               Console.WriteLine("Error: " + e);
               Console.WriteLine(e.StackTrace);
           }
           finally
           {
               conn.Close();
               conn.Dispose();
           }

           Console.Read();
       }
   }

}
Running the example:

10- ExecuteScalar

MySqlCommand.ExecuteScalar()  is a method used to execute SQL statements, it returns the value of the first column of the first row in results of SQL statements.
-- The following statement returns only one value.

Select count(*) from Employee;

-- Or

Select Max(e.Salary) From Employee e;
Example:
ExecuteScalarExample.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;
using System.Data;
using Tutorial.SqlConn;


namespace CsMySQLTutorial
{
   class ExecuteScalarExample
   {
       static void Main(string[] args)
       {
           MySqlConnection conn = DBUtils.GetDBConnection();
           conn.Open();
           try
           {
               MySqlCommand cmd = new MySqlCommand("Select count(*) From Employee", conn);
               
               cmd.CommandType = CommandType.Text;

               // ExecuteScalar return first column of first row.
               object countObj =  cmd.ExecuteScalar();

               int count = 0;
               if (countObj != null)
               {
                   count = Convert.ToInt32(countObj);
               }

               Console.WriteLine("Emp Count: " + count);

           }
           catch (Exception e)
           {
               Console.WriteLine("Error: " + e);
               Console.WriteLine(e.StackTrace);
           }
           finally
           {
               conn.Close();
               conn.Dispose();
           }

           Console.Read();
       }
   }
}
Running the example: