内部联接的实体框架查询

Question

什么是查询:

select s.* from Service s 
inner join ServiceAssignment sa on sa.ServiceId = s.Id
where  sa.LocationId = 1

在实体框架中？

这就是我写的:

 var serv = (from s in db.Services
                join sl in Location on s.id equals sl.id
                where sl.id = s.id
                select s).ToList();

但这是错的.有人可以指导我走这条路吗？

Answer 1

from s in db.Services
join sa in db.ServiceAssignments on s.Id equals sa.ServiceId
where sa.LocationId == 1
select s

db你的位置在哪里DbContext？生成的查询看起来像(EF6的示例):

SELECT [Extent1].[Id] AS [Id]
       -- other fields from Services table
FROM [dbo].[Services] AS [Extent1]
INNER JOIN [dbo].[ServiceAssignments] AS [Extent2]
    ON [Extent1].[Id] = [Extent2].[ServiceId]
WHERE [Extent2].[LocationId] = 1

Answer 2

如果有人对Method语法感兴趣,如果你有一个导航属性,那很容易:

db.Services.Where(s=>s.ServiceAssignment.LocationId == 1);

如果你不这样做,除非有一些Join()我不知道的覆盖,我认为它看起来很粗糙(我是一个方法语法纯粹主义者):

db.Services.Join(db.ServiceAssignments, 
     s => s.Id,
     sa => sa.ServiceId, 
     (s, sa) => new {service = s, asgnmt = sa})
.Where(ssa => ssa.asgnmt.LocationId == 1)
.Select(ssa => ssa.service);

Answer 3

如果可用,您可以使用导航属性.它在SQL中生成内部联接.

from s in db.Services
where s.ServiceAssignment.LocationId == 1
select s