SQLHelper

　　　　 /// <summary>
        /// 获取连接字符串
        /// </summary>
        private static readonly string constr = ConfigurationManager.ConnectionStrings["dbUser"].ConnectionString;

        /// <summary>
        /// 返回受影响行数（非查询语句）
        /// </summary>
        /// <param name="sql">SQL语句</param>
        /// <param name="parameters">参数化查询</param>
        /// <returns></returns>
        public static int ExecuteNonQuery(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(constr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    return cmd.ExecuteNonQuery();
                }
            }
        }

        /// <summary>
        /// 返回查询结果集中的第一行第一列
        /// </summary>
        /// <param name="sql">SQL语句</param>
        /// <param name="parameters">参数化查询</param>
        /// <returns></returns>
        public static object ExecuteScalar(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(constr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    return cmd.ExecuteScalar();
                }
            }
        }

        /// <summary>
        /// 返回查询结果有多条数据，数据放在数据库中
        /// </summary>
        /// <param name="sql">SQL语句</param>
        /// <param name="parameters">参数化查询</param>
        /// <returns></returns>
        public static SqlDataReader ExecuteReader(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection())
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    return cmd.ExecuteReader();
                }
            }
        }

        /// <summary>
        /// 返回查询结果有多条数据，数据放在本地缓存中
        /// </summary>
        /// <param name="sql">SQL语句</param>
        /// <param name="parameters">参数化查询</param>
        /// <returns></returns>
        public static DataTable ExecuteDataSet(string sql, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(constr))
            {
　　　　　　　　　 conn.Open()
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);

                    DataSet dataset = new DataSet();
                    SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                    adapter.Fill(dataset);
                    return dataset.Tables[0];
                }
            }
        }

        /// <summary>
        /// 将数据库中的Null转化为null
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static object OutputNull(object value)
        {
            if (value == DBNull.Value)
                return null;
            else
                return value;
        }

        /// <summary>
        /// 将输入数据的null转化为数据库中Null
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static object InputNull(object value)
        {
            if (value == null)
                return DBNull.Value;
            else
                return value;
        }

    }