Child Table Properties are not fetching in ef core inheritance

Question

i have following entities..

    public class Paper
    {
        public int Id { get; set; }
        public string PaperCode { get; set; }
        ...
    }
    public class MCQPaper : Paper
    {
        public ICollection<MCQQuestion> Questions { get; set; }
    }
    public class MCQQuestion : Question
    {
        public int MCQPaperId { get; set; }
        public MCQPaper MCQPaper { get; set; }

        public int? MCQOptionId { get; set; }
        [ForeignKey("MCQOptionId")]
        public MCQOption TrueAnswer { get; set; }
        public ICollection<MCQOption> MCQOptions { get; set; }
    }
    public class MCQOption
    {
        public int Id { get; set; }
        public string OptionText { get; set; }
    }

and i am trying to fetch MCQPaper based on unique papercode but it always gives me empty collection of Questions

here is my Query inside Repository..

        public MCQPaper GetByPaperCode(string paperCode)
        {
            var ans = AppDbContext.MCQPapers
                .Where(paper => paper.PaperCode.Equals(paperCode))
                //.Include(paper => paper.Questions)
                //    .ThenInclude(que => que.MCQOptions)
                .Include(paper => paper.Questions)
                    .ThenInclude(que => que.MCQPaper)
                //.Include(paper => paper.Questions)
                //    .ThenInclude(que => que.TrueAnswer)
                .FirstOrDefault();
            return ans;
        }

here i have tried various combinations of include() and theninclude() but none of them work for me

and lastly ignore grammer mistakes if any

thankyou in advance

are you tried to put where after the include ? remove where and put your condition to FirstOrDefaut() .FirstOrDefault(paper => paper.PaperCode.Equals(paperCode)); — puko
– puko, Commented Oct 16, 2020 at 5:20
are you sure that you have some questions inserted in database ? with right foreign key ? — puko
– puko, Commented Oct 16, 2020 at 5:35
Check this article learnentityframeworkcore.com/configuration/… — puko
– puko, Commented Oct 16, 2020 at 5:41

Janak Vaghasiya · Accepted Answer · 2020-10-16 07:22:42Z

after going threw comments and searching on google i have found solution

using two queries this problem can be solved because here i have circular dependency between MCQQuestion and MCQOption

so solution is ....

        public MCQPaper GetByPaperCode(string paperCode)
        {
            using var transaction = AppDbContext.Database.BeginTransaction();
            MCQPaper ans = new MCQPaper();
            try
            {
                ans = AppDbContext.MCQPapers
                .FirstOrDefault(paper => paper.PaperCode.Equals(paperCode));
                var questions = AppDbContext.MCQQuestions
                    .Include(que => que.MCQOptions)
                    .Where(que => que.MCQPaperId == ans.Id);
                ans.Questions = questions.ToList();
                transaction.Commit();
            }
            catch (Exception)
            {
                transaction.Rollback();
            }
            return ans;
        }

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