在LINQ查询中，我能否有一个对孙子起作用的where子句？

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问题描述

我有三个表，每个表都有一个主键和一个外键，例如 TestId 和 UserTestId 等.

Exam > Test > UserTest

据我了解，我可以使用 LINQ 从这些数据中获取数据，如下所示:

        var exams = _examsRepository
       .GetAll()
       .Where(q => q.SubjectId == subjectId)
       .Include(q => q.Tests.Select(t => t.UserTests))
       .ToList();

这将选择所有考试，考试的测试和 SubjectId == subjectID 的那些测试的 UserTests

是否有任何可能的方法可以进一步限制这一点，以便仅显示 UserTests 的 UserId 为 123 时的数据?

如果答案是否定的，那么我是否应该重写此 LINQ 以首先转到 _userTestsRepository，然后朝另一个方向向上而不是向下工作?

解决方案

在这个问题他们提供的解决方案可以满足您的需求，但在我看来，这有点像 hack.
或者，您可以放弃包含语句并进行手动连接，您可以根据需要在子表上应用尽可能多的过滤器.
可能看起来像这样:

var data = (from ex in context.exams
           join t in context.tests on ex.Id equals test.ExamID
           join ut in context.userTests on t.Id equals ut.TestId
           where ut.UserId = 123
           select new {ex, ut}).ToList();

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问题描述

I have three tables that are each connected with a primary key and foreign key such as TestId and UserTestId etc.

Exam > Test > UserTest

It's my understanding I can use LINQ to get the data from these like this:

        var exams = _examsRepository
       .GetAll()
       .Where(q => q.SubjectId == subjectId)
       .Include(q => q.Tests.Select(t => t.UserTests))
       .ToList();

This will select all the exams, Tests for the exams and UserTests for those Tests where SubjectId == subjectID

Is there any possible way I could further limit this so that it only showed the data for when the UserTests had a UserId of 123?

If the answer is no then should I rewrite this LINQ to first go to the _userTestsRepository and then work in the other direction up instead of down?

推荐答案

In this question they offer a solution which does what you want but in my opinion feels a little like a hack.
Alternatively you could step away from include statements and do a manual join, you can apply as many filters on sub tables as you like that way.
Could look a lil like this :

var data = (from ex in context.exams
           join t in context.tests on ex.Id equals test.ExamID
           join ut in context.userTests on t.Id equals ut.TestId
           where ut.UserId = 123
           select new {ex, ut}).ToList();

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