SqlHelper

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

namespace SqlHelper
{
    public static class SqlHelper
    {
        /// <summary>
        /// 数据库连接字符串字段，默认取值配置文件
        /// </summary>
        private static string strConn = ConfigurationManager.ConnectionStrings[ConfigurationManager.AppSettings["DCS"]].ConnectionString;
        /// <summary>
        /// 根据默认配置创建一个SqlConnection对象
        /// </summary>
        private static SqlConnection conn = new SqlConnection(strConn);
        private static SqlCommand cmd = new SqlCommand();
        private static SqlTransaction tran = null;

        /// <summary>
        /// 数据库连接字符串属性，可重新设置数据库连接字符串
        /// </summary>
        public static string ConnectionString
        {
            get
            {
                return strConn;
            }

            set
            {
                strConn = value;
                // 数据库连接字符串更改时，同时更改SqlConnection的ConnectionString属性
                conn.ConnectionString = strConn;
            }
        }

        /// <summary>
        /// 获取SqlConnection对象
        /// </summary>
        public static SqlConnection Connection
        {
            get
            {
                return conn;
            }
        }

        static SqlHelper()
        {
            if (conn.State != ConnectionState.Open)
            {
                conn.Open();
            }
        }

        #region 读取数据

        public static T ExecuteScalar<T>(CommandType commandType, string commandText, params SqlParameter[] parms)
        {
            PrepareCommand(cmd, conn, null, commandType, commandText, parms);

            object result = cmd.ExecuteScalar();
            Close();
            if (result != null)
            {
                return (T)Convert.ChangeType(result, typeof(T));
            }

            return default(T);
        }

        public static SqlDataReader ExecuteDataReader(CommandType commandType, string commandText, params SqlParameter[] parms)
        {
            PrepareCommand(cmd, conn, null, commandType, commandText, parms);
            return cmd.ExecuteReader(CommandBehavior.CloseConnection);
        }

        public static DataSet ExecuteDataSet(CommandType commandType, string commandText, params SqlParameter[] parms)
        {
            PrepareCommand(cmd, conn, null, commandType, commandText, parms);
            SqlDataAdapter da = new SqlDataAdapter(cmd);

            DataSet ds = new DataSet();
            da.Fill(ds);
            Close();
            return ds;
        }

        public static DataTable ExecuteDataTable(CommandType commandType, string commandText, params SqlParameter[] parms)
        {
            return ExecuteDataSet(commandType, commandText, parms).Tables[0];
        }

        #endregion

        #region 增、删、改（无事务处理）

        public static int ExecuteNonQuery(CommandType commandType, string commandText, params SqlParameter[] parms)
        {
            PrepareCommand(cmd, conn, null, commandType, commandText, parms);
            int count = cmd.ExecuteNonQuery();
            Close();
            return count;
        }

        #endregion

        #region 增、删、改（带事务处理）

        public static void BeginTransaction()
        {
            if(conn.State==ConnectionState.Closed)
            {
                conn.Open();
            }
            tran = conn.BeginTransaction();
        }
       
        public static void CommitTransaction()
        {
            tran.Commit();
            Close();
        }

        public static void RollbackTransaction()
        {
            tran.Rollback();
            Close();
        }

        public static int ExecuteNonQueryWithTransaction(CommandType commandType, string commandText, params SqlParameter[] parms)
        {
            PrepareCommand(cmd, conn, tran, commandType, commandText, parms);
            int count = cmd.ExecuteNonQuery();
            return count;
        }

        #endregion

        private static void PrepareCommand(SqlCommand command, SqlConnection connection, SqlTransaction transaction, CommandType commandType, string commandText, SqlParameter[] parms)
        {
            if (connection.State != ConnectionState.Open)
            {
                connection.Open();
            }
          
            // 设置数据库连接
            command.Connection = connection;
            // 设置命令文本(存储过程名或SQL语句)
            command.CommandText = commandText;
            // 设置命令类型.
            command.CommandType = commandType;
            // 分配事务
            if (transaction != null)
            {
                command.Transaction = transaction;
            }

            // 清除SqlCommand的参数
            command.Parameters.Clear();

            if (parms != null && parms.Length > 0)
            {
                // 预处理SqlParameter参数数组，将为NULL的参数赋值为DBNull.Value;
                foreach (SqlParameter parameter in parms)
                {
                    if ((parameter.Direction == ParameterDirection.InputOutput || parameter.Direction == ParameterDirection.Input) && (parameter.Value == null))
                    {
                        parameter.Value = DBNull.Value;
                    }
                }
                command.Parameters.AddRange(parms);
            }
        }

        /// <summary>
        /// 关闭连接
        /// </summary>
        private static void Close()
        {
            if(conn.State== ConnectionState.Open)
            {
                conn.Close();
            }
            
        }
    }
}