DataBase: MySQL在.NET中的应用

首先需要下载MySQL:

1. 官方下载

dev.mysql.com/downloads/mysql/

2. 解压到你所想要安装的位置，在文件夹里创建my.ini文件

[mysql]
# 设置mysql客户端默认字符集
default-character-set=gbk
[mysqld]
#设置3306端口
port = 3306 
# 设置mysql的安装目录
basedir=D:mysqlmysql-5.6.17-winx64
# 设置mysql数据库的数据的存放目录
datadir=D:mysqlmysql-5.6.17-winx64data
# 允许最大连接数
max_connections=200
# 服务端使用的字符集默认为8比特编码的latin1字符集
character-set-server=gbk
# 创建新表时将使用的默认存储引擎
default-storage-engine=INNODB 

 这里要把路径改掉

3. 用管理员身份运行cmd.exe， 到bin文件里运行：mysqld install，在任务管理器的服务中开启mysql服务

4. 在cmd.exe中设置root密码：mysqladmin -u root -p password

5. 登录mysql：mysql -u root -p

6. 设置路径：将mysql所安装文件夹的bin路径加入

7. 可以用到的一些指令：show databases; show tables; describe [table]; source 

8. 建议用下Navicat for mysql这个软件

在使用C#连mysql前需要下载.NET与mysql的连接器

http://dev.mysql.com/downloads/connector/net

一。数据读取

与MySQL进行数据读取的步骤是：

1. 连接数据源

2. 打开连接

3. 创建一个SQL查询命令

4. 用DataReader或者DataSet读取数据

5. 关闭连接

下面是以DataReader为例的数据读取

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlCommand cmd = new MySqlCommand("SELECT * FROM students", con);
            MySqlDataReader reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                Console.WriteLine("	{0}	{1}", reader["Name"], reader["Grade"]);
            }
            reader.Close();
            con.Close();
        }
    }
}

下面是用DataSet来读取数据

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;
using System.Data;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlDataAdapter adapter = new MySqlDataAdapter("SELECT * FROM students", con);
            DataSet ds = new DataSet();
            adapter.Fill(ds, "students");
            foreach (DataRow row in ds.Tables["students"].Rows)
            {
                Console.WriteLine(row["Name"] + "	" + row["Grade"]);
            }
            con.Close();
        }
    }
}

一般我们偏向用DataSet来进行操作，因为数据更新用DataSet会更加方便

二。数据更新

不需要用SQL的update语句，直接用SqlCommandBuilder就可以更新数据库了

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;
using System.Data;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlDataAdapter adapter = new MySqlDataAdapter("SELECT * FROM students", con);
            MySqlCommandBuilder builder = new MySqlCommandBuilder(adapter);
            DataSet ds = new DataSet();
            adapter.Fill(ds, "students");
            Console.WriteLine("Grade before change: {0}", ds.Tables["students"].Rows[0]["Grade"]);
            ds.Tables["students"].Rows[0]["Grade"] = "19";
            adapter.Update(ds, "students");
            Console.WriteLine("Grade after change: {0}", ds.Tables["students"].Rows[0]["Grade"]);
            con.Close();
        }
    }
}

注意adapter.Update方法的datatable名字必须与前面的fill方法一致

增加一行，判断是不是已经存在了，if语句中为了保证Add()成功，必须在添加操作成功后马上调用Find()方法

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;
using System.Data;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlDataAdapter adapter = new MySqlDataAdapter("SELECT * FROM students", con);
            MySqlCommandBuilder builder = new MySqlCommandBuilder(adapter);
            DataSet ds = new DataSet();
            adapter.Fill(ds, "students");
            Console.WriteLine("# rows before change: {0}", ds.Tables["students"].Rows.Count);
            DataColumn[] keys = new DataColumn[1];
            keys[0] = ds.Tables["students"].Columns["Name"];
            ds.Tables["students"].PrimaryKey = keys;
            DataRow findRow = ds.Tables["students"].Rows.Find("wangnaiyu");
            if (findRow == null)
            {
                Console.WriteLine("wangnaiyu not found, will add to students table");
                DataRow newRow = ds.Tables["students"].NewRow();
                newRow["Name"] = "wangnaiyu";
                newRow["Age"] = "28";
                newRow["Grade"] = "70";
                ds.Tables["students"].Rows.Add(newRow);
                if ((findRow = ds.Tables["students"].Rows.Find("wangnaiyu")) != null)
                {
                    Console.WriteLine("wangnaiyu successfully added to students table");
                }
            }
            else
            {
                Console.WriteLine("wangnaiyu already present in database");
            }
            adapter.Update(ds, "students");
            Console.WriteLine("# rows after change: {0}", ds.Tables["students"].Rows.Count);
            con.Close();
        }
    }
}

删除行

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;
using System.Data;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlDataAdapter adapter = new MySqlDataAdapter("SELECT * FROM students", con);
            MySqlCommandBuilder builder = new MySqlCommandBuilder(adapter);
            DataSet ds = new DataSet();
            adapter.Fill(ds, "students");
            Console.WriteLine("# rows before change: {0}", ds.Tables["students"].Rows.Count);
            DataColumn[] keys = new DataColumn[1];
            keys[0] = ds.Tables["students"].Columns["Name"];
            ds.Tables["students"].PrimaryKey = keys;
            DataRow findRow = ds.Tables["students"].Rows.Find("wangnaiyu");
            if (findRow != null)
            {
                Console.WriteLine("wangnaiyu already in students table");
                Console.WriteLine("Removing wangnaiyu ...");
                findRow.Delete();
                adapter.Update(ds, "students");
            }
            Console.WriteLine("# rows after change: {0}", ds.Tables["students"].Rows.Count);
            con.Close();
        }
    }
}

访问多个表

这里用DataRelations类，DataSet建立关系是用DataSet.Relations.Add(DataRelation);的。而DataRelation的构造函数为DataRelation(string relationName, DataColumn parentColumn, DataColumn, childColumn);注意这里的父子关系不要弄错，父表中的一行对应子表中的多行，用DataRow.GetChildRows(DataRelation)可以得到的子表中对应的行DataRow[]。具体看下面的代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;
using System.Data;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlDataAdapter stuAdapter = new MySqlDataAdapter("SELECT * FROM students", con);
            MySqlCommandBuilder stuBuilder = new MySqlCommandBuilder(stuAdapter);
            MySqlDataAdapter orderAdapter = new MySqlDataAdapter("SELECT * FROM Orders", con);
            MySqlCommandBuilder orderBuilder = new MySqlCommandBuilder(orderAdapter);
            DataSet ds = new DataSet();
            stuAdapter.Fill(ds, "students");
            orderAdapter.Fill(ds, "Orders");
            DataRelation stuOrderRel = ds.Relations.Add("StuOrders", ds.Tables["students"].Columns["Name"], ds.Tables["Orders"].Columns["Name"]);
            foreach (DataRow stuRow in ds.Tables["students"].Rows)
            {
                Console.WriteLine("Student Name: " + stuRow["Name"] + " Age: " + stuRow["Age"] + " Grade: " + stuRow["Grade"]);
                foreach (DataRow orderRow in stuRow.GetChildRows(stuOrderRel))
                {
                    Console.WriteLine(" Order: " + orderRow["Order"]);
                }
            }
            con.Close();
        }
    }
}

如果要从子表中取得父表中的数据，可以通过GetParentRow()。

三。直接执行SQL命令

一般DataSet中存储的数据很大，如果操作不是很多，则用SQL命令来操作效率会快很多

可以通过下面的程序看看SQL语句

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;
using System.Data;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlDataAdapter adapter = new MySqlDataAdapter("SELECT * FROM students", con);
            MySqlCommandBuilder builder = new MySqlCommandBuilder(adapter);
            Console.WriteLine("SQL SELECT Command is: {0}
", adapter.SelectCommand.CommandText);
            Console.WriteLine("SQL UPDATE Command is: {0}
", builder.GetUpdateCommand().CommandText);
            Console.WriteLine("SQL INSERT Command is: {0}
", builder.GetInsertCommand().CommandText);
            Console.WriteLine("SQL DELETE Command is: {0}
", builder.GetDeleteCommand().CommandText);
            con.Close();
        }
    }
}

ExecuteScalar返回的是结果

ExecuteNonQuery返回的是修改操作影响的行数

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;
using System.Data;

namespace test4
{
    class Program
    {
        static void Main(string[] args)
        {
            MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true");
            con.Open();
            MySqlCommand cmd = new MySqlCommand("SELECT COUNT(*) FROM students", con);
            Object res = cmd.ExecuteScalar();
            Console.WriteLine("Count of students = {0}", res);
            
            cmd.CommandText = "UPDATE students SET Age = 29 WHERE Grade = 88";
            int rowsAffected = cmd.ExecuteNonQuery();
            Console.WriteLine("Rows Update = {0}", rowsAffected);
            con.Close();
        }
    }
}

 数据库的操作一般都需要加上异常机制，另外MySqlConnection也是一个需要关闭的类，用using可能会来得更方便些，在MySqlCommand语句里可以用@variable的方式增加变量，在后面用Command.Parameters来选择特定值。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using MySql.Data;
using MySql.Data.Entity;
using MySql.Data.MySqlClient;
using System.IO;

namespace MysqlTest
{
    class Program
    {
        static void Main(string[] args)
        {
            using (MySqlConnection con = new MySqlConnection("server=localhost; database=persons; uid=root; pwd=0000; connect timeout=30; pooling=true"))
            {
                MySqlCommand cmd = new MySqlCommand("SELECT * FROM students where Name = @Name", con);
                try
                {
                    con.Open();
                    cmd.Parameters.Add("@Name", MySqlDbType.VarChar);
                    cmd.Parameters["@Name"].Value = "yingzhongwen";
                    MySqlDataReader reader = cmd.ExecuteReader();
                    while (reader.Read())
                    {
                        Console.WriteLine("	{0}	{1}", reader["Name"], reader["Grade"]);
                    }
                    reader.Close();
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
            }

        }
    }
}

 Parameter的操作还可以这样：

MySqlParameter parameters = new MySqlParameter("@Name", MySqlDbType.VarChar);
parameters.Value = "yingzhongwen";
cmd.Parameters.Add(parameters);