如何在LINQ查询中包括多个层次? [英] How can I include more than one level deep in a LINQ query?

问题描述

我有三个用类表示的SQL表，并且我想让Entity Framework 6加入这些表，以便获得Exam，Test和UserTest表的所有详细信息，其中UserTest.UserID是0或X.

I have three SQL tables that are represented by classes and I would like to have Entity Framework 6 join these tables so I get all the details of the Exam, Test and UserTest tables where the UserTest.UserID is 0 or X.

我已经建立了一个存储库，该存储库适用于简单查询，但是我无法在问题底部加入LINQ中的UserTest类.

I have already set up a respository and this works for simple queries however I am unable to join the UserTest class in the LINQ at the bottom of the question.

这是我的课程:

public class Exam
{
    public int ExamId { get; set; }
    public int SubjectId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Test> Tests { get; set; }
}

public class Test
{
    public int TestId { get; set; }
    public int ExamId { get; set; }
    public string Title { get; set; }
    public virtual ICollection<UserTest> UserTests { get; set; }
}

public class UserTest
{
    public int UserTestId { get; set; }
    public string UserId { get; set; }
    public int TestId { get; set; }
    public int QuestionsCount { get; set; }
}

我想做的是查询看起来像这样的东西:

What I would like to do is to have a query that looks something like this:

var exams = _examsRepository
           .GetAll()
           .Where(q => q.SubjectId == subjectId)
           .Include(q => q.Tests )
           .Include(q => q.Tests.UserTests) // Error on this line
           .ToList();

但是，这并不能让我在VS2013中包含UserTests.

But it's not letting me include UserTests in VS2013.

更新:

这是我第一次尝试的查询:

Here is the query I first tried:

  var userTests = _userTestsRepository
        .GetAll()
        .Include(t => t.Test)
        .Include(t => t.Test.Exam)
        .Where(t => t.UserId == "0" || t.UserId == userId);

这似乎很有效，但是当我查看输出时，看到的是这样的:

This one seemed to work however when I looked at the output I saw something like this:

[{"userTestId":2,
  "userId":"0",
  "testId":12,
  "test":{
      "testId":12,"examId":1,
      "exam":{
          "examId":1,"subjectId":1,
          "tests":[
               {"testId":13,"examId":1,"title":"Sample Test1",
                "userTests":[
                      {"userTestId":3,
                       "userId":"0",

请注意，这种情况开始重复出现，并带来了比我预期更多的数据

Note that this starts to repeat and bring back a lot more data than I expected

推荐答案

这是因为Tests是一个集合，而不仅仅是一个对象，因此它没有UserTests属性.您可以使用lambda来指定多个孩子而不是一个孩子的孙子:

That's because Tests is a collection and not just a single object, so it doesn't have a UserTests property. You use a lambda to specify grandchildren of multiple children rather than a single child:

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

请注意，不需要两个Include调用，因为如果要包括孙子项，则隐式包括子项.

Note that there's no need for two Include calls because the children are implicitly included if you're including the grandchildren.

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