Question

我已经花了足够的时间，所以我需要stackoverflow的帮助。

这是一个实体

Entity: Asset 
Field: AssetVersionID (int) PK
Field: AssetID (int) FK
Field: ReleaseTimestamp (DateTime)

我的任务是选择具有唯一AssetID和最新ReleaseTimestamp的资产。基本上我需要这样的功能

public IQueryable<Asset> GetAssets(List<int> assetIds)

SQL中的

看起来像这样：

select a1.* 
from Assets as a1
join (
        select t.AssetID, max(t.ReleaseTimestamp) as ReleaseTimestamp
        from Asssets as t
        where AssetID in (1,2,3,4,5)
        goup by AssetID
    ) as a2
on a1.AssetID = a2.AssetID and a1.ReleaseTimestamp= a2.ReleaseTimestamp

如何使用EF和LINQ进行操作？

我试过了：

public IQueryable<Asset> GetAssets(List<int> assetUIds)
{
 IQueryable<Asset> assets = _context.Assets.Where(a => assetUIds.Contains(a.UID));
 var ff = assets.GroupBy(a => a.UID, a => a,
              (uid, p2) => new {KEY = uid, rel = p2.Max(p2a => p2a.ReleaseTimestamp)});
 IQueryable<Asset> assets2 = _context.Assets;

 var assets3 = from ass1 in assets2
          join ass2 in ff on new {ass1.UID, ass1.ReleaseTimestamp} equals new {ass2.KEY, ass2.rel}
          select ass1;
 return assets3;
}

但是我在“加入”附近有语法错误基本上这是有效的：

join ass2 in ff on ass1.UID equals ass2.KEY

这不是

join ass2 in ff on new {ass1.UID, ass1.ReleaseTimestamp} equals new {ass2.KEY, ass2.rel}

一如既往：）

请帮助！

Answer 1

您加入的表达方式必须相同。将其更改为：

join ass2 in ff on new {KEY = ass1.UID, rel = ass1.ReleaseTimestamp} equals new {ass2.KEY, ass2.rel}

实体框架：join方法

1 个答案: