Question

我正在尝试以下方法：

     var questions = _questionsRepository
            .GetAll()
            .Where(q => q.Problem.SubTopicId == subTopicId || subTopicId == 0)
            .Where(q => q.QuestionStatusId == questionStatusId || questionStatusId == 0)
            .Where(q => q.AssignedTo == assignedTo || assignedTo == "0")
            .Where(q => q.ModifiedBy == modifiedBy || modifiedBy == "0")
            .Include(q => q.Problem)
            .Include(q => q.Answers)
            .Select(x=>new Question {
                QuestionId = x.QuestionId,
                QuestionUId = x.QuestionUId,
                Answers = x.Answers,
                Problem = new Problem {
                    ProblemId = x.Problem.ProblemId
                }
            }).ToList();

但收到错误消息说：

System.NotSupportedException was unhandled by user code
  HResult=-2146233067
  Message=The entity or complex type 'Models.Contexts.Question' cannot be constructed in a LINQ to Entities query.
  Source=EntityFramework
  StackTrace:

Answer 1

您的类问题似乎不是存储库/上下文的一部分，因此EF无法在SQL中构造此类的对象。但是，您可以在SQL中获取所有必需的数据，并在获得所有数据后在.net中构造对象。要指示此switch-to-.net，您可以使用AsEnumerable()方法。

var questions = _questionsRepository
    .GetAll()
    .Where(q => q.Problem.SubTopicId == subTopicId || subTopicId == 0)
    .Where(q => q.QuestionStatusId == questionStatusId || questionStatusId == 0)
    .Where(q => q.AssignedTo == assignedTo || assignedTo == "0")
    .Where(q => q.ModifiedBy == modifiedBy || modifiedBy == "0")
    .Include(q => q.Problem)
    .Include(q => q.Answers)
    .Select(x => new {
        QuestionId = x.QuestionId,
        QuestionUId = x.QuestionUId,
        Answers = x.Answers,
        ProblemId = x.Problem.ProblemId
    })
    .AsEnumerable()
    .Select(x => new Question {
        QuestionId = x.QuestionId,
        QuestionUId = x.QuestionUId,
        Answers = x.Answers,
        Problem = x.ProblemId
    })
    .ToList();

Answer 2

与实体The entity cannot be constructed in a LINQ to Entities query重复。查看此帖子以了解您无法直接在您的选择关闭中实例化实体。您必须创建一个DTO类来使用。

解决方案也是：

var questions = _questionsRepository
        .GetAll()
        .Include("Problem")
        .Include("Answers")
        .Where(q => (q.Problem.SubTopicId == subTopicId || subTopicId == 0) 
               && (q.QuestionStatusId == questionStatusId || questionStatusId == 0)
               && (q.AssignedTo == assignedTo || assignedTo == "0")
               && (q.ModifiedBy == modifiedBy || modifiedBy == "0")).ToList();

你应该得到你想要的东西。

我可以使用LINQ to Entities查询选择这样的选项吗？

2 个答案: