ado.net五大对象

五大对象分别是：

1、 Connection：与数据源建立连接。

2、 Command：对数据源执行SQL命令并返回结果。

3、 DataReader：读取数据源的数据，只允许对将数据源以只读、顺向的方式查看其中所存储的数据。其常用于检索大量数据，DataReader对象还是一种非常节省资源的数据对象。

4、 DataAdapter：对数据源执行操作并返回结果，在DataSet与数据源之间建立通信，将数据源中的数据写入DataSet中，或根据DataSet中的数据绑定数据源。

5、 DataSet：内存中的数据库，是数据表的集合，它可以包含任意多个数据表。

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class UserBLL {         public const string constring = "User Id=root;Host=localhost;Database=dbdemo;password=wdf123;charset='utf8'";         //添加数据         public int Add(User entity) {             string sql = "insert into User(ID,UserName)Value(?ID,?UserName)";             using (MySqlConnection conn = new MySqlConnection(constring)) {                 conn.Open();                 MySqlCommand command = new MySqlCommand(sql,conn);                 command.Parameters.AddWithValue("?ID",entity.ID);                 command.Parameters.AddWithValue("?UserName", entity.UserName);                 return command.ExecuteNonQuery();             }         }         //修改数据         public int Update(User entity) {             string sql = "update User set UserName=?UserName where ID=?ID";             using (MySqlConnection conn = new MySqlConnection(constring)) {                 conn.Open();                 MySqlCommand command = new MySqlCommand(sql, conn);                 command.Parameters.AddWithValue("?ID", entity.ID);                 command.Parameters.AddWithValue("?UserName", entity.UserName);                 return command.ExecuteNonQuery();             }         }         //删除数据         public int Delete(int ID) {             string sql = "delete from User where ID=?ID";             using (MySqlConnection conn = new MySqlConnection(constring)) {                 conn.Open();                 MySqlCommand command = new MySqlCommand(sql, conn);                 command.Parameters.AddWithValue("?ID", ID);                 return command.ExecuteNonQuery();             }         }         //根据主键查询         public User Get(int ID) {             string sql = "select ID,UserName from User where ID=?ID";             using (MySqlConnection conn = new MySqlConnection(constring)) {                 conn.Open();                 MySqlCommand command = new MySqlCommand(sql, conn);                 command.Parameters.AddWithValue("?ID", ID);                 MySqlDataReader reader = command.ExecuteReader();                 User user = null;                 if (reader.Read()) {                     user = new User();                     user.ID = Convert.ToInt32(reader["ID"]);                     user.UserName = reader["UserName"].ToString();                 }                 return user;             }         }         //查询集合         public IList<User> GetList() {             string sql = "select* from User";             using (MySqlConnection conn = new MySqlConnection(constring)) {                 conn.Open();                 MySqlCommand command = new MySqlCommand(sql, conn);                 MySqlDataReader reader = command.ExecuteReader();                 IList<User> list = new List<User>();                 while(reader.Read()){                     User user = new User();                     user.ID = Convert.ToInt32(reader["ID"]);                     user.UserName = reader["UserName"].ToString();                     list.Add(user);                 }                 return list;             }         }       }