EF Core adding object nulls a navigation property

Question

I am trying to add a Drink object via DbContext, but after adding the drink using the context, the Brand property becomes null. What could be the reason for this?

(Ignore the double _context add method, was debugging)

Before adding the drink After adding the drink

Models:

public class Product
{
    [Key]
    public string Id { get; set; }
    public string Name { get; set; }
}

public class Drink : Product
{
    public Brand Brand { get; set; }
    public Category Category { get; set; }
    public ICollection<DrinkTag> DrinkTags { get; set; }
}


public class Brand
{
    [Key]
    public string Name { get; set; }

    public ICollection<Drink> Drinks { get; set; }
}

public class Category
{
    [Key]
    public string Name { get; set; }

    public ICollection<Drink> Drinks { get; set; }
}

public class Tag
{
    [Key]
    public string Name { get; set; }

    public ICollection<Drink> Drinks { get; set; }
}

public class DrinkTag
{
    public string DrinkId { get; set; }
    public Drink Drink { get; set; }
    public string TagId { get; set; }
    public Tag Tag { get; set; }
}

Forget the navigation property, can you explain why drink.Name property changed? — Smit
– Smit, Commented Jun 11, 2017 at 7:22
@Smit I didn't notice that. These 2 screenshots were right after each other. I definitely was not changing anything via the watch list so I have no idea how it could have changed. — Stein121
– Stein121, Commented Jun 12, 2017 at 9:56
Can you share more code about your controller? Especially the method being called & how the DbContext is being injected — Smit
– Smit, Commented Jun 12, 2017 at 17:17

Cristian Szpisjak · Accepted Answer · 2017-06-01 13:30:27Z

1

Your Drink model:

public class Drink : Product
{
    public int BrandId { get; set; }

    // Navigational properties
    public Brand Brand { get; set; }
    public Category Category { get; set; }
    public ICollection<DrinkTag> DrinkTags { get; set; }
}

When you add a new Drink specify only the BrandId:

var myDrink = new Drink();
myDrink.BrandId = 2;
// ... and so on

Also, EF Core does not load the related properties automatically. So if you want the Brand loaded you need to manually do it like:

var data = myContext.Drinks
    .Include(p => p.Brand)
    .FirstOrDefault(p => p.Id == yourId);

edited Jun 1, 2017 at 13:30

answered Jun 1, 2017 at 13:23

Cristian Szpisjak

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3 Comments

Stein121 Over a year ago

I am not loading, I am creating.

Cristian Szpisjak Over a year ago

Where's your relation defined between those 2 tables?

Stein121 Over a year ago

The adding of the brand via a BrandId property works but do you know why the navigation property would be null after adding it via the context?

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