Question

我的问题是以下查询返回零记录。但是数据库中有记录。

我的目标SubjectQuestion选择Subjectid的表格获得相同的问题模型。

我该怎么办？帮助你谢谢你。

[我的模特]

SubjectQuestion

public  class SubjectQuestion
{
    public int Id { get; set; }
    public int SubjectId { get; set; }
    public int QuestionId { get; set; }
    public virtual List<Question.Question> Question { get; set; }
}

问题

public class Question
{
    public int Id { get; set; }
    public int QuestionNo { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
    public bool IsDeleted { get; set; }
    public QuestionModel ToModel()
   {
       return new QuestionModel(Id,QuestionNo,Title,Description,ChoiceId);
   }    
}

QuestionModel

public class QuestionModel
{
    public QuestionModel(int id, int questionNo, string title, string description,int choiceid)
    {
        Id = id;
        QuestionNo = questionNo;
        Title = title;
        Description = description;
        ChoiceId = choiceid;
    }
    public int Id { get; set; }
    public int QuestionNo { get; set; } 
    public string Title { get; set; }
    public string Description { get; set; }
    public bool IsDeleted { get; set; } 
}

实体框架查询

List<QuestionModel> lst = _db.SubjectQuestions.Where(x => x.SubjectId == subjectId).ToList().SelectMany(r=> r.Question.Select(y=> y.ToModel()).ToList()).ToList();

Answer 1

主要问题在这里

_db.SubjectQuestions.Where(x =>
  x.SubjectId == subjectId).ToList()

此时您正在针对SubjectQuestions执行查询，因此EF只会带来该表而不是问题列表。如果您对问题使用Include语句，则应该修复它。

_db.SubjectQuestions.Include(x => x.Questions).Where(x =>
  x.SubjectId == subjectId).ToList()

另外，如果是我，我会在你的问题课上明确表达与SubjectQuestions的关系（通过包含一个SubjectQuestion属性，可能还有一个Id）。那么查询就是

_db.Questions.Where(x =>
  x.SubjectQuestion.SubjectId == subjectId).ToList().Select(y=> y.ToModel())

Answer 2

解决

SubjectQuestion

char

实体框架嵌套表关系SelectMany

2 个答案: