Web Api + Entity Framework Not properly loading data

Question

I've built a small service using the ASP.NET Web Api. My domain classes looks like this:

 public class Drink : IEntity
{
    public Drink()
    {
        Ingridients = new List<Ingredient>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Ingredient> Ingridients { get; set; }
    public string Approach { get; set; }
}

public class Ingredient : IEntity
{
    public Ingredient()
    {
        Drinks = new List<Drink>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Drink> Drinks { get; set; }
}

My Repository Looks like this:

public IEnumerable<T> GetAll(){return _dbSet;}

And my controller looks like this:

    public IEnumerable<Drink> GetAllDrinks()
    {
        return _unitOfWork.Drinks.GetAll();
    }

When I make I request using fiddler the JSON result is the following:

{"Id":15,"Name":"Russian Energy","Ingridients":[],"Approach":"Mix Vodka with Redbull"}

As you can see the Ingridents array is empty. Why is that?

I added the json.net tag because this question is really, "why doesn't json.net serialize my EF graph correctly." Web-api is incidental to the problem. — Darrel Miller, Jan 05 '13 at 16:41
Have a look at this question on SO .. http://stackoverflow.com/questions/5588143/ef-4-1-code-first-json-circular-reference-serialization-error — Rajesh, Jan 14 '13 at 15:11
Also have a look at this blog that might be helpful: http://blog.davebouwman.com/2011/12/08/handling-circular-references-asp-net-mvc-json-serialization/ — Rajesh, Jan 14 '13 at 15:19
Looks interesting, Rajesh. I'll have a cloer look at it ASAP — Ols1, Jan 17 '13 at 19:50

score 2 · Answer 1 · answered Jan 05 '13 at 17:03

2

You can try to use eager loading with Include:

Extend your GetAll method to allow eager loading:

//...
using System.Data.Entity;
//...

public IEnumerable<T> GetAll(params Expression<Func<T, object>>[] includes)
{
    IQueryable<T> query = _dbSet;
    if (includes != null)
    {
        foreach (var include in includes)
            query = query.Include(include);
    }
    return query;
}

Then use it in your controller like so:

public IEnumerable<Drink> GetAllDrinks()
{
    return _unitOfWork.Drinks.GetAll(d => d.Ingredients);
}

answered Jan 05 '13 at 17:03

Slauma

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Now I get a different error..like so An error has occurred. The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'. System.InvalidOperationException An error has occurred. Object graph for type 'Gudo.Core.Model.Ingredient' contains cycles and cannot be serialized if reference tracking is disabled. – Ols1 Jan 05 '13 at 17:50
This error occurs after I applied the changes that Slauma suggested – Ols1 Jan 05 '13 at 17:51
@IAmSharp: Google for the error or ask a new question. There plenty of references about this problem over the Internet. For example: http://stackoverflow.com/a/658056/270591 or (for JSON.NET) http://johnnycode.com/2012/04/10/serializing-circular-references-with-json-net-and-entity-framework/ The error has nothing to do with your original problem that the ingredients are not loaded. – Slauma Jan 05 '13 at 18:19
Ok..I'll add a new question – Ols1 Jan 05 '13 at 19:37

score 0 · Answer 2 · answered Jan 05 '13 at 15:11

Are you using Entity Framework Code First?

If so, you have to mark the navigation properties as virtual:

public class Drink : IEntity
{
    public Drink()
    {
        Ingridients = new List<Ingredient>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Ingredient> Ingridients { get; set; }
    public string Approach { get; set; }
}

public class Ingredient : IEntity
{
    public Ingredient()
    {
        Drinks = new List<Drink>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Drink> Drinks { get; set; }
}

Yes, I'm using CF. Marking the nav properties as virtual didn't help. I'm still getting the empty array. — Ols1, Jan 05 '13 at 15:17

Web Api + Entity Framework Not properly loading data

2 Answers2