07ADO.Net

using (MySqlConnection conn &＃61; new MySqlConnection("Server&＃61;localhost;Database&＃61;study1;uid&＃61;root;pwd&＃61;root;Charset&＃61;utf8"))
using (MySqlCommand cmd &＃61; conn.CreateCommand())
{conn.Open();//一定要在执行前Open数据库连接cmd.CommandText &＃61; "Insert into T_Users(UserName,Password) values(&＃39;中国人&＃39;,&＃39;123&＃39;)";int rowCount &＃61; cmd.ExecuteNonQuery();Console.WriteLine("受影响的行数"&＃43;rowCount);
}

cmd.CommandText &＃61; "Select count(*) from T_Users";//查询命令&＃xff1a;查询T_Users表的总数据条数
long count &＃61; (long)cmd.ExecuteScalar();//执行查询命令后获得的结果是一行一列的

using(MySqlConnection conn &＃61; new MySqlConnection("Server&＃61;localhost;Database&＃61;study1;uid&＃61;root;pwd&＃61;root;Charset&＃61;utf8"))
using (MySqlCommand cmd &＃61; conn.CreateCommand())
{conn.Open();//查询命令&＃xff0c;查询用户名是amdin的密码cmd.CommandText &＃61; "select password from T_Users where UserName&＃61;&＃39;admin&＃39;";//执行查询命令并接收返回的查询命令查询结果string pwd &＃61; (string)cmd.ExecuteScalar();//判断查询结果是否为空&＃xff0c;空则没有查询到if (string.IsNullOrEmpty(pwd)){Console.WriteLine("没有找到用户");}else{Console.WriteLine("密码是&＃xff1a;"&＃43;pwd);}
}
Console.ReadKey();

//创建连接对象
using(MySqlConnection conn &＃61; new MySqlConnection("Server&＃61;127.0.0.1;Database&＃61;study1;uid&＃61;root;pwd&＃61;root;Charset&＃61;utf8"))
using (MySqlCommand cmd &＃61; conn.CreateCommand())//创建命令对象
{conn.Open();cmd.CommandText &＃61; "select * from T_Users";using (MySqlDataReader reader &＃61; cmd.ExecuteReader()){conn.Close();//Reader读取的时候要保持Connection连接while (reader.Read())//Reader的好处是&＃xff1a;即使查询数据量大&＃xff0c;客户端内存也不会明显增加
{//获得数据库里各个字段的值int id &＃61; reader.GetInt32("Id");string username &＃61; reader.GetString("UserName");string password &＃61; reader.GetString("PassWord");Console.WriteLine("Id&＃61;"&＃43;id&＃43;";UserName&＃61;"&＃43;username&＃43;";PassWord&＃61;"&＃43;password);}}
}
Console.ReadKey();

static void Main(string[] args)
{using (MySqlConnection conn &＃61; new MySqlConnection("Server&＃61;127.0.0.1;Database&＃61;study1;uid&＃61;root;pwd&＃61;root;Charset&＃61;utf8"))using (MySqlCommand cmd &＃61; conn.CreateCommand()){conn.Open();//把要插入的值用参数传递 &＃64;un &＃64;pwd cmd.CommandText &＃61; "insert into T_Users(UserName,PassWord) Values(&＃64;un,&＃64;pwd)";//填充这个参数cmd.Parameters.Add(new MySqlParameter { ParameterName &＃61; "&＃64;un", Value &＃61; "黎庆煌" });cmd.Parameters.Add(new MySqlParameter { ParameterName &＃61; "&＃64;pwd", Value &＃61; "123" });//执行MySql语句int count &＃61; cmd.ExecuteNonQuery();Console.WriteLine("影响行数&＃xff1a;" &＃43; count);}Console.ReadKey();
}

//int i &＃61; 0;
//cmd.Parameters.Add(new MySqlParameter("&＃64;Age", i));
//cmd.Parameters.Add(new MySqlParameter("&＃64;Age", 0));
cmd.Parameters.Add(new MySqlParameter("&＃64;Age",(object)0));//可以强制转换这样做避免这个陷阱

using(MySqlConnection conn &＃61; new MySqlConnection("Server&＃61;127.0.0.1;Database&＃61;study1;uid&＃61;root;pwd&＃61;root;Charset&＃61;utf8"))
using (MySqlCommand cmd &＃61; conn.CreateCommand())
{conn.Open();cmd.CommandText &＃61; "select * from T_Users";using (MySqlDataReader reader &＃61; cmd.ExecuteReader()){while (reader.Read()){string username &＃61; reader.GetString("UserName");//string password &＃61; reader.GetString("PassWord");string password;if (reader.IsDBNull(reader.GetOrdinal("PassWord"))){password &＃61; null;}else{//GetString/GetInt32无法读取数据库中的null值//需要提前用IsDBNull判断password &＃61; reader.GetString("PassWord");}int? age;if (reader.IsDBNull(reader.GetOrdinal("Age"))){age &＃61; null;}else{age &＃61; reader.GetInt32("Age");}//int age &＃61; reader.GetInt32("Age");Console.WriteLine("用户名&＃xff1a;"&＃43;username&＃43;"&＃xff1b;密码&＃xff1a;"&＃43;password&＃43;"&＃xff1b;年龄&＃xff1a;"&＃43;age);}}
}
Console.ReadKey();

DataSet ds &＃61; new DataSet();
MySqlDataAdapter adapter &＃61; new MySqlDataAdapter(cmd);
adapter.Fill(ds);
DataTable table &＃61; ds.Tables[0];

MySqlTransaction tx &＃61; conn.BeginTransaction();//启动事务
try
{MySqlHelper.ExecuteNonQuery(conn, "Update t_accounts Set Amount&＃61;Amount-1000 where Number&＃61;&＃39;0001&＃39;");string s &＃61; null;s.ToLower();MySqlHelper.ExecuteNonQuery(conn, "Update t_accounts Set Amount&＃61;Amount&＃43;1000 where Number&＃61;&＃39;0002&＃39;");tx.Commit();//执行到这&＃xff0c;没有错误则提交事务
}
catch (Exception ex)
{tx.Rollback();//如果过程中出现任何错误则执行回滚&＃xff08;当前事务操作全部取消&＃xff09;
}