/// <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())            {                using (SqlCommand cmd = conn.CreateCommand())                {                    cmd.CommandText = sql;                    cmd.Parameters.AddRange(parameters);                    DataSet dataset = new DataSet();                    SqlDataAdapter adapter = new SqlDataAdapter();                    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 =http://www.mamicode.com/= 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 =http://www.mamicode.com/= null)                return DBNull.Value;            else                return value;        }    }