using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;
using System.Data.SqlClient;

namespace Sql1
{
    /// <summary>
    /// SQL助手
    /// 
    /// 封装：抽取变化的 封装不变的
    /// </summary>
    public class SQLHelper
    {
        //连接字符串--连接数据库用
        private static readonly string connString = @"Data Source=DESKTOP-9JEHCP6;Initial Catalog=StudentManage;User ID=**;Password=**;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False";
//增、删、改(insert、delete、update)
        #region 增、删、改(insert、delete、update)


        /// <summary>
        /// 增、删、改(insert、delete、update)
        /// </summary>
        /// <param name="sql">SQL语句</param>
        /// <returns></returns>
        public static int GetSingleResult(string sql)
        {
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql, conn);
            try
            {
                //这部分是写需要检测的语句
                conn.Open();
                int result = cmd.ExecuteNonQuery();
                return result;
            }
            catch (Exception ex)
            {
                //处理异常
                //会直接显示或者可以写入系统日志
                Console.WriteLine("执行GetSingleResult(string sql)方法出错" + ex.Message);
                throw ex;
            }
            finally
            {
                //最后需要处理的问题
                conn.Close();
            }
        }
        #endregion


//读取单个对象
        #region 读取单个对象
        /// <summary>
        /// 读取单一结果
        /// </summary>
        /// <param name="sql">SQL语句</param>
        /// <returns></returns>
        public static object GetSingleObject(string sql)
        {
            //连接ADO.net做数据查询
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand cmd = new SqlCommand(sql,conn);
            try
            {
                conn.Open();
                //using System.Data;
                //CommandBehavior.CloseConnection 检测并自动关闭数据库连接
                //object reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                object obj = cmd.ExecuteScalar();
                return obj;
            }
            catch (Exception ex)
            {
                //处理异常
                //会直接显示或者可以写入系统日志
                Console.WriteLine("执行GetSingleObject(string sql)方法出错" + ex.Message);
                throw ex;
            }
            finally
            {
                conn.Close();
            }
        }

        #endregion

//读取多个对象
        #region 读取多个对象
        /// <summary>
        /// 读取多个对象
        /// </summary>
        /// <param name="sql">SQL语句</param>
        /// <returns></returns>
        public static SqlDataReader GetDataReader(String sql)
        {
            //连接ADO.NET做数据查询
            SqlConnection conn = new SqlConnection(connString);//连接数据库(连接数据库实例)
            SqlCommand cmd = new SqlCommand(sql, conn); // 发送sql命令
            try
            {
                conn.Open(); //打开数据库连接
                //CommandBehavior.CloseConnection 检测并自动关闭数据库连接
                SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                return reader;
            }
            catch (Exception ex)
            {
                //处理异常
                //会直接显示或者可以写入系统日志
                Console.WriteLine("执行GetDataReader(string sql)方法出错" + ex.Message);
                throw ex;
            }

        }
        #endregion
    }
}

6. SQL数据库增删改查方法封装