C# 我如何创建一个LINQ表达式来连接四个表并允许在最上面的表上使用where？

我有以下课程：

public partial class Topic
{
    public Topic()
    {
        this.SubTopics = new List<SubTopic>();
    }
    public int TopicId { get; set; }
    public string Name { get; set; }
    public int SubjectId { get; set; }
    public virtual Subject Subject { get; set; }
    public virtual ICollection<SubTopic> SubTopics { get; set; }
}
public partial class SubTopic
{    
    public SubTopic()
    {
        this.Problems = new List<Problem>();
    }
    public int SubTopicId { get; set; }
    public int TopicId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Problem> Problems { get; set; }
    public virtual Topic Topic { get; set; }

}
public class Problem
{
    public Problem()
    {
        this.Questions = new List<Question>();
    }
    public int ProblemId { get; set; }
    public int SubTopicId { get; set; }
    public string Title { get; set; }
    public virtual SubTopic SubTopic { get; set; }
    public virtual ICollection<Question> Questions { get; set; }
}
public class Question
{
    public int QuestionId { get; set; }
    public int ProblemId { get; set; }
    public string Text { get; set; }
    public virtual Problem Problem { get; set; }
}

---

为此，有人能告诉我如何使LINQ表达式连接上述所有表，以便输入SubjectId=0

您拥有所需的所有导航属性，因此只需执行以下操作：

var questions = _questionsRepository.GetAll()
.Where(m => m.Problem.SubTopic.Topic.SubjectId == 0)
.Select(m => m.QuestionId);

您可能需要一些空检查

.Where(m => m.Problem != null && 
            m.Problem.SubTopic ! null && 
            m.Problem.SubTopic.Topic != null &&
            m.Problem.SubTopic.Topic.SubjectId == 0)
.Select(m => m.QuestionId);

---

您拥有所需的所有导航属性，因此只需执行以下操作：

var questions = _questionsRepository.GetAll()
.Where(m => m.Problem.SubTopic.Topic.SubjectId == 0)
.Select(m => m.QuestionId);

您可能需要一些空检查

.Where(m => m.Problem != null && 
            m.Problem.SubTopic ! null && 
            m.Problem.SubTopic.Topic != null &&
            m.Problem.SubTopic.Topic.SubjectId == 0)
.Select(m => m.QuestionId);