Question

I’m building an ASP.NET MVC 3 site using the code-first Entity Framework 4 approach. I have one object in my model, Problem, that contains a child collection of another model object, ProblemRating. Currently I have the Problem model set up as follows:

public class ProblemModel
{
    [Key]
    [Required]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ProblemId { get; set; }

    [Display(Name = "Creator")]
    [Required]
    public string UserName { get; set; }

    [Required]
    public string Title { get; set; }

    [Required]
    public string ProblemDescription { get; set; }

    [Required]
    public string InputDescription { get; set; }

    [Required]
    public string InputSample { get; set; }

    [Required]
    public string OutputDescription { get; set; }

    [Required]
    public string OutputSample { get; set; }

    public virtual IEnumerable<ProblemRatingModel> Ratings { get; set; }

    public DateTime CreatedDate { get; set; }

    public DateTime LastModifiedDate { get; set; }
}

The ProblemRating class is pretty simple:

public class ProblemRatingModel
{
    [ForeignKey("AssociatedProblem")]
    public int AssociatedProblemId { get; set; }
    public ProblemModel AssociatedProblem { get; set; }
    public string UserName { get; set; }
    public decimal Rating { get; set; }
}

The boilerplate code in the Create method of the controller isn’t reporting a valid model when I fill out the fields and click “Create”:

if (ModelState.IsValid)
{
    db.ProblemModels.Add(problemmodel);
    db.SaveChanges();
    return RedirectToAction("Index");  
}

return View(problemmodel);

What is the correct way to handle child collections of a model inside another model class? I’m not 100% sure about the usage of the ForeignKey attribute either, am I using that correctly?

Thanks!

Answer 1

Change your ProblemModel class as follows

public class Problem //Renamed to Problem
{
    ...

    public virtual ICollection<ProblemRating> Ratings { get; set; }

    ...
}

…and in you ProblemRating vlass do the following

public class ProblemRating // Renamed to ProblemRating
{
    public int Id { get; set; } 
    public int ProblemId { get; set; }
    public string UserName { get; set; }
    public decimal Rating { get; set; }

    public virtual Problem Problem { get; set; }

}

The wizardary of EF code first (handy naming assumptions) will do the rest for you.

Check this out
http://weblogs.asp.net/scottgu/archive/2010/07/16/code-first-development-with-entity-framework-4.aspx

You can also remove the key attributes on your Problem Id column