扩展Lambda

5.x文档地址

http://www.donet5.com/Home/Doc

该方法可以让Lambda支持自定义解析, 可以把数据库的自带函数封装起来, 享受一个完美的ORM

当然, 该方法不仅仅只是支持查询里面使用, 对应的查询, 修改, 删除都可以使用自定义Lambda解析, 这里用查询做Demo

    public class Demo
    {
        public static SqlSugarClient GetDb()
        {
            //Create ext method
            var expMethods = new List<SqlFuncExternal>();
            expMethods.Add(new SqlFuncExternal()
            {
                UniqueMethodName = "MyToString",
                MethodValue = (expInfo, dbType, expContext) =>
                {
                    if(dbtype=DbType.SqlServer)
                     return string.Format("CAST({0} AS VARCHAR(MAX))", expInfo.Args[0].MemberName);
                    else
                     throw new Exception("未实现")'
                }
            });

            var config = new ConnectionConfig()
            {
                ConnectionString = Config.ConnectionString,
                DbType = DbType.SqlServer,
                IsAutoCloseConnection = true,
                ConfigureExternalServices = new ConfigureExternalServices()
                {
                    SqlFuncServices = expMethods//set ext method
                }
            };

            SqlSugarClient db = new SqlSugarClient(config);
            return db;
        }

        public static string MyToString<T>(T str)
        {
            throw new NotSupportedException("Can only be used in expressions");
        }

        public static void Init()
        {
            var db = GetDb();
            var list = db.Queryable<Student>().Where(it => MyToString(it.Id) == "1302583").ToList();
            var sql = db.Queryable<Student>().Where(it => MyToString(it.Id) == "1302583").ToSql();
            //生成的Sql CAST([Id] AS VARCHAR(MAX))
            Console.WriteLine(sql);
        }
    }