自己写的SqlHelper

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;

namespace resume.Helper
{
    public static class SqlHelper
    {
        public static readonly string connstr =
           ConfigurationManager.ConnectionStrings["liuyan"].ConnectionString;

        public static SqlConnection OpenConnection()
        {
            SqlConnection conn = new SqlConnection(connstr);
            conn.Open();
            return conn;
        }
        /// <summary>
        /// 执行非查询语句，并返回受影响的行数
        /// </summary>
        /// <param name="cmdText"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public static int ExecuteNonQuery(string cmdText,
            params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                return ExecuteNonQuery(conn, cmdText, parameters);
            }
        }

        public static object ExecuteScalar(string cmdText,
            params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                return ExecuteScalar(conn, cmdText, parameters);
            }
        }

        public static DataTable ExecuteDataTable(string cmdText,
            params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                return ExecuteDataTable(conn, cmdText, parameters);
            }
        }

        /// <summary>
        /// 执行非查询语句，并返回受影响的行数
        /// </summary>
        /// <param name="conn"></param>
        /// <param name="cmdText"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public static int ExecuteNonQuery(SqlConnection conn, string cmdText,
           params SqlParameter[] parameters)
        {
            using (SqlCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = cmdText;
                cmd.Parameters.AddRange(parameters);
                return cmd.ExecuteNonQuery();
            }
        }

        public static object ExecuteScalar(SqlConnection conn, string cmdText,
            params SqlParameter[] parameters)
        {
            using (SqlCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = cmdText;
                cmd.Parameters.AddRange(parameters);
                return cmd.ExecuteScalar();
            }
        }

        public static DataTable ExecuteDataTable(SqlConnection conn, string cmdText,
            params SqlParameter[] parameters)
        {
            using (SqlCommand cmd = conn.CreateCommand())
            {
                cmd.CommandText = cmdText;
                cmd.Parameters.AddRange(parameters);
                using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
                {
                    DataTable dt = new DataTable();
                    adapter.Fill(dt);
                    return dt;
                }
            }
        }

        public static object ToDBValue(this object value)
        {
            return value == null ? DBNull.Value : value;
        }

        public static object FromDBValue(this object dbValue)
        {
            return dbValue == DBNull.Value ? null : dbValue;
        }
    }
}

下面是数据库连接字符串，写程序的时候经常要用不可能我们自己总是写，这样的习惯不是很好的。

<connectionStrings>
    <add name="连接字符串" connectionString="server =数据库地址; initial catalog =数控库名; uid = sa; pwd =123456789"
      providerName="System.Data.SqlClient" />
  </connectionStrings>