sql增删改查封装

App.config文件

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <connectionStrings>
    <add connectionString="Data Source = .; Initial Catalog = mysql; Integrated Security = True;" name="conStr" />
  </connectionStrings>
</configuration>

sqlHelper封装类库代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
//新建一个App.confit文件，引用下面两个命名空间
using System.Configuration;
using System.Data.SqlClient;

namespace 封装
{
    public class SqlHelper
    {
        //读取连接字符串
        private static readonly string str = ConfigurationManager.ConnectionStrings["conStr"].ConnectionString;
        //三个方法，关键是第三个方法，查询，条件判断比较多
        /// <summary>
        /// 此方法可以做增删改
        /// </summary>
        /// <param name="sql">sql语句</param>
        /// <param name="ps">sql语句中的参数</param>
        /// <returns>返回受影响的行数，int类型</returns>
        private static int ExecuteNonQuery(string sql, params SqlParameter[] ps)
        {
            using (SqlConnection con = new SqlConnection(str))
            {
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {
                    con.Open();
                    if (ps != null)
                    {
                        cmd.Parameters.AddRange(ps);
                    }

                    return cmd.ExecuteNonQuery();
                }
            }
        }
        /// <summary>
        /// 该方法用在查询上
        /// </summary>
        /// <param name="sql">sql语句</param>
        /// <param name="ps">sql语句中的参数</param>
        /// <returns>返回首行首列，object类型</returns>
        private static object ExecuteScalar(string sql, params SqlParameter[] ps)
        {
            using (SqlConnection con = new SqlConnection(str))
            {
                using (SqlCommand cmd = new SqlCommand(sql, con))
                {
                    con.Open();
                    if (ps != null)
                    {
                        cmd.Parameters.AddRange(ps);
                    }
                    return cmd.ExecuteScalar();
                }
            }
        }
        /// <summary>
        /// 该方法用于查询，读数据
        /// </summary>
        /// <param name="sql">sql语句</param>
        /// <param name="ps">sql语句中的参数</param>
        /// <returns>返回sqldatareader对象，里面有数据</returns>
        private static SqlDataReader ExecuteReader(string sql, params SqlParameter[] ps)
        {
            //这地方不用using，因为不知道什么时候释放
            SqlConnection con = new SqlConnection(str);
            using (SqlCommand cmd = new SqlCommand(sql,con))
            {
                if (ps!=null)
                {
                    cmd.Parameters.AddRange(ps);
                }
                try
                {
                    con.Open();
                    //这个重载会datareader关闭时，自动关闭connection
                    return cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
                }
                catch (Exception ex)
                {
                    con.Close();
                    con.Dispose();
                    throw ex;
                }
            }
        }
    }
}