在 EF core 中,我正在尝试投影一个带有子集合的结果集。
然而,当执行这个操作时,BNames集合是惰性的,所以当它被枚举时,它会为每一行触发一个单独的查询,例如在B的集合中有2个项目。
在EF6中,同样的查询结果如下(正如我所期望的):
我该如何让EF预先加载子集合
注意:这不同于使用
完整代码库在此处:https://gist.github.com/lukemcgregor/692834629da09b21d5a35515e86c9002
ctx.As.Select(a => new
{
AId = a.Id,
BNames = a.Bs.Select(x=>x.Name) //SubCollection
})
然而,当执行这个操作时,BNames集合是惰性的,所以当它被枚举时,它会为每一行触发一个单独的查询,例如在B的集合中有2个项目。
[a].[Id] AS [AId] FROM [As] AS [a]
p_executesql N'SELECT [x].[Name]
FROM [Bs] AS [x]
WHERE @_outer_Id = [x].[AId]',N'@_outer_Id int',@_outer_Id=1
p_executesql N'SELECT [x].[Name]
FROM [Bs] AS [x]
WHERE @_outer_Id = [x].[AId]',N'@_outer_Id int',@_outer_Id=2
在EF6中,同样的查询结果如下(正如我所期望的):
SELECT
[Extent1].[Id] AS [Id],
[Project1].[C1] AS [C1],
[Project1].[Name] AS [Name]
FROM [dbo].[A] AS [Extent1]
LEFT OUTER JOIN (SELECT
[Extent2].[Name] AS [Name],
[Extent2].[A_Id] AS [A_Id],
1 AS [C1]
FROM [dbo].[B] AS [Extent2] ) AS [Project1] ON [Extent1].[Id] = [Project1].[A_Id]
ORDER BY [Extent1].[Id] ASC, [Project1].[C1] ASC
我该如何让EF预先加载子集合
BNames
?注意:这不同于使用
.Include
包含子实体的问题,因为这是一个自定义投影,而不是导航属性。在此处使用.Include
会导致错误。完整代码库在此处:https://gist.github.com/lukemcgregor/692834629da09b21d5a35515e86c9002