ADO.net基础学习总结

ADO.net是一门.net连接、操作数据库的技术

 

释放资源：凡是实现了idisposable借口的类都需要用using来释放资源

using（）

{

}

连接数据库

                     //创建数据库连接：
                    using（SqlConnection conn=new SqlConnection("连接字符串")）//连接字符串
                    {
                    conn.open();//打开连接
                    using（SqlCommand cmd =conn.CreateCommd()）
                    {
                    cmd.CommadTest="sql 语句";
　　　　　　　　　　　　......

在线数据连接方式:

参数化查询：

                    cmd.CommadText="select * from T_Student where name =@name add age=@age;"
 
                    cmd.Parameters.add(new SqlParameter("@name", txtName.text))；//给参数赋值
 
                    cmd.Parameters.add(new SqlParameter("@age", Convert.ToInt32(txtAge.text)))；//给参数赋值

ExcuteNonquery一般用于非查询语句（insert，delete，update）

                    cmd.CommandText = "insert into T_a (name , age ) values (@name,@age);";
                    cmd.Parameters.Add(new SqlParameter("@name", txtName.Text));
                    cmd.Parameters.Add(new SqlParameter("@age", txtAge.Text));
                    int count= cmd.ExecuteNonQuery();
                    MessageBox.Show(count+"行受影响")

ExcuteScalar一般用与执行返回值只有一行一列的sql语句

                    cmd.CommandText = "select age from T_a where Id=@id and name =@name;";
                    cmd.Parameters.Add(new SqlParameter("@id", txtID.Text));
                    cmd.Parameters.Add(new SqlParameter("@name", txtName.Text));
                    try
                    {
                        string age = cmd.ExecuteScalar().ToString();
                        MessageBox.Show(age);
                    }
                    catch
                    {
                        MessageBox.Show("找不到匹配的值");
                    }

ExcuteReader用于sql查询语句，查询结果放在数据库中，占用服务器资源，返回类型为SqlDateReader类型

                    cmd.CommandText = "select * from T_a;";
                    SqlDataReader reader = cmd.ExecuteReader();
                    while (reader.Read())
                    {
                        long id = reader.GetInt64(0);
                        string name = reader.GetString(1);
                        int age = reader.GetInt32(2);
                        MessageBox.Show(id + "," + name + "," + age);
                    }

离线数据连接方式:

Dataset查询结果读取到客户端本地，适合数据量较少的查询

                      cmd.CommandText = "select * from T_a where name = @name;";
                    //参数化查询
                    cmd.Parameters .Add (new SqlParameter("@name",txtName.Text));
                    SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                    //创建Dataset数据集
                    DataSet dataset = new DataSet();
                    //将查询结果填入Dataset中
                    adapter.Fill(dataset);
                    DataTable table = dataset.Tables[0];
                    DataRowCollection rows = table.Rows;
                    //遍历每一行的值
                    foreach (DataRow row in rows )
                    {
                       long id = (long)row["id"];
                       string name = (string)row["name"];
                       int age = (int)row["age"];
                       MessageBox .Show (id+","+name+","+age);
                    }