如何修复 "LINQ to Entities does not recognize the method 'System.DateTime GetValueOrDefault()'"？

Question

我有这个代码。基本上我需要更改日期并告诉用户今天商店将从上午 10 点营业到晚上 10 点。所以这里的时间是固定的。

来自:-

today_date = "2020-03-23T00:00:00"

start_hour_time = "1900-01-01T10:00:00"

end_hour_time = "1900-01-01T22:00:00"

更改为：-

start_newdatetime = "2020-03-23T10:00:00"

end_newdatetime = "2020-03-23T22:00:00"

DateTime todaysdate = DateTime.Now.Date;       

var find_date = bdb.tbl_store
        .Join(bdb.tbl_hour, a => a.start_hour_id, b => b.hour_id, (a, b) => new { a, b })
        .Join(bdb.tbl_hour, a => a.a.end_hour_id, b => b.hour_id, (a, b) => new { a, b })
        .Where(x => x.a.a.store_id == store_id )
        .Select(x => new {

        x.a.a.store_id,
        start_hour_time = x.a.b.hour_time,
        end_hour_time = x.b.hour_time,
        start_newdatetime = todaysdate.Date+ x.a.b.hour_time.GetValueOrDefault().TimeOfDay,
        end_newdatetime = todaysdate.Date + x.b.hour_time.GetValueOrDefault().TimeOfDay

    }) .ToList();

现在的问题，是错误。因为我希望它在同一个变量上。

"Message": "An error has occurred.", "ExceptionMessage": "LINQ to Entities does not recognize the method 'System.DateTime
GetValueOrDefault()' method, and this method cannot be translated into a store expression.", "ExceptionType": "System.NotSupportedException",

但如果我为 return 新值创建另一个变量就没问题了。

Answer 1

您的表达式似乎不起作用，因为成员 GetValueOrDefault 和 TimeOfDay 不可用于 EF DB 查询翻译，因此您将不得不以某种方式解决该问题。目前我无法验证，但我认为以下应该是可能的

var find_date = bdb.tbl_store
        .Join(bdb.tbl_hour, a => a.start_hour_id, b => b.hour_id, (a, b) => new { a, b })
        .Join(bdb.tbl_hour, a => a.a.end_hour_id, b => b.hour_id, (a, b) => new { a, b })
        .Where(x => x.a.a.store_id == store_id )
        .ToList()
        .Select(x => new {
            x.a.a.store_id,
            start_hour_time = x.a.b.hour_time,
            end_hour_time = x.b.hour_time,
            start_newdatetime = todaysdate.Date + x.a.b.hour_time.GetValueOrDefault().TimeOfDay,
            end_newdatetime = todaysdate.Date + x.b.hour_time.GetValueOrDefault().TimeOfDay
    }).ToList();

这样，您的查询在调用 ToList 时是运行，其他所有内容（传递给 Select 的 Lambda 表达式）在客户端上作为纯 C# 执行，因此确实存在实体没有理由抱怨。诚然，我不确定调用 ToList 时这些对象是否已完全解析。如果不是这样，你可以这样做

var find_date = bdb.tbl_store
        .Join(bdb.tbl_hour, a => a.start_hour_id, b => b.hour_id, (a, b) => new { a, b })
        .Join(bdb.tbl_hour, a => a.a.end_hour_id, b => b.hour_id, (a, b) => new { a, b })
        .Where(x => x.a.a.store_id == store_id)
        .Select(x => new {
            x.a.a.store_id,
            start_hour_time = x.a.b.hour_time,
            end_hour_time = x.b.hour_time 
        })
        .ToList()
        .Select(x => new {
            store_id,
            start_hour_time,
            end_hour_time,
            start_newdatetime = todaysdate.Date + start_hour_time.GetValueOrDefault().TimeOfDay,
            end_newdatetime = todaysdate.Date + end_hour_time.GetValueOrDefault().TimeOfDay
        }).ToList();

如何修复 "LINQ to Entities does not recognize the method 'System.DateTime GetValueOrDefault()'"？

How to fix "LINQ to Entities does not recognize the method 'System.DateTime GetValueOrDefault()'"?

c#

linq

datetime

linq-to-entities