How to show choices of the question in view using ASP.NET Core?

I’m creating an online exam. I want to show the choices for each question in view.when I run the program it has an error “null reference”.

This is my Question table:

public class Question
{
    [Key]
    public int QuestionId { get; set; }//1
    public int ExamId { get; set; }
    public string UserId { get; set; }
    public string QuestionTitle { get; set; }
    public decimal Grade { get; set; }

    #region relations
    [ForeignKey("UserId")]
    public virtual IdentityUser IdentityUser { get; set; }
    public Exam exam { get; set; }
    public List<ChoiceQuestionSelection> choiceQuestionSelection { get; set; }
    #endregion
}

This is my choices table:

public class ChoiceQuestionSelection
{
    [Key]
    public int ChoiceQuestionSelectionId { get; set; }
    public int QuestionId { get; set; }
    public string Choice { get; set; }
    public bool IsTrue { get; set; }
    public string FeedbackTrue { get; set; }
    public string FeedbackFalse { get; set; }

    #region relations
    public Question question { get; set; }
    #endregion
}

This is my view:

@foreach (var item in Model)
{
    <div class="col-lg-6">
        <div class="well well-lg">
            <h4>@item.QuestionTitle</h4>
            <h6>@item.Grade </h6>
            <p>
            @if (item.choiceQuestionSelection.Any(q => q.QuestionId == item.QuestionId))
            {
                @foreach (var choice in item.choiceQuestionSelection)
                {
                    <label>
                        <input type="radio" name="optionsRadios" id="optionsRadios1" value="option1" 
                     checked="">@choice.Choice
                    </label>
                }
            }
        </p>
    </div>
</div>
}

This is the action method:

public IActionResult ShowQuestions(int id)
{
    return View(_questionService.GetAllQuestions(id));
}

This is the method:

public List<Question> GetAllQuestions(int examId)
{
    return _context.questions
                   .Where(q => q.ExamId == examId).ToList();
}

I have some choices in my choice table for a question but it doesn’t show them. What should I write in my query?

Answers:

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Method 1

When you load your questions from the database, you have to include choiceQuestionSelection otherwise it would not be loaded

_context.Questions.Include(q => q.choiceQuestionSelection).Where(q => q.ExamId == examId);

Also, in case choiceQuestionSelection is empty, you must initialize it as an empty list to prevent a null reference when you call it.

public class Question 
{
    public Question()
    {
        choiceQuestionSelection = new List<choiceQuestionSelection>{};
    }
    public List<ChoiceQuestionSelection> choiceQuestionSelection { get; set; }
}

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0