How to add where clause to ThenInclude

Question

I have 3 entities:

Questionnaire.cs:

public class Questionnaire
{
    public int Id { get; set; }
    public string Name { get; set; }
          


        

Answer 1

Filtering in Include or IncludeThen is not supported. Create projection by using Select:

questionnaire = _context.Questionnaires
    .Select(n => new Questionnaire
    {
        Id = n.Id,
        Name = n.Name,
        Questions = n.Questions.Select(q => new Question
        {
           Id = q.Id,
           Text = q.Text,
           Answers = q.Where(a => a.UserId == userId).ToList()
        }).ToList()
    })
    .FirstOrDefault(qn => qn.Id == questionnaireId);

There is a github issue about this problem: https://github.com/aspnet/EntityFramework/issues/3474