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
– Darrel Miller, Commented Jan 5, 2013 at 16:41
Have a look at this question on SO .. stackoverflow.com/questions/5588143/… — Rajesh
– Rajesh, Commented Jan 14, 2013 at 15:11
Also have a look at this blog that might be helpful: blog.davebouwman.com/2011/12/08/… — Rajesh
– Rajesh, Commented Jan 14, 2013 at 15:19
Looks interesting, Rajesh. I'll have a cloer look at it ASAP — Ols1
– Ols1, Commented Jan 17, 2013 at 19:50

Slauma · Accepted Answer · 2013-01-05 17:03:41Z

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 5, 2013 at 17:03

Slauma

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4 Comments

Ols1 Over a year ago

Now I get a different error..like so <Error> <Message>An error has occurred.</Message> <ExceptionMessage> The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'. </ExceptionMessage> <ExceptionType>System.InvalidOperationException</ExceptionType> <StackTrace/> <InnerException> <Message>An error has occurred.</Message> <ExceptionMessage> Object graph for type 'Gudo.Core.Model.Ingredient' contains cycles and cannot be serialized if reference tracking is disabled. </ExceptionMessage>

Ols1 Over a year ago

This error occurs after I applied the changes that Slauma suggested

Slauma Over a year ago

@IAmSharp: Google for the error or ask a new question. There plenty of references about this problem over the Internet. For example: stackoverflow.com/a/658056/270591 or (for JSON.NET) johnnycode.com/2012/04/10/… The error has nothing to do with your original problem that the ingredients are not loaded.

Ols1 Over a year ago

Ok..I'll add a new question

deerchao · Accepted Answer · 2013-01-05 15:11:22Z

0

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; }
}

answered Jan 5, 2013 at 15:11

deerchao

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1 Comment

Ols1 Over a year ago

Yes, I'm using CF. Marking the nav properties as virtual didn't help. I'm still getting the empty array.

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