How to Detect Change on 1-N

Question

Simple question. I didn't have this problem using NHibernate, but now I have it with EntityFramework:

Imagine that I have a Car, with a list of Tires.

I want to remove 1 tire of a car, so I want to update it. Something like:

Car.Tires.Remove(tire);

And then I update the car object with this update method:

public virtual void Update(T obj)
{
     TryAttach(obj);
     SetAllModified(obj);
     SaveChanges();
}

The problem is that after the update, the car still have the same amount of tires.

How can I update the list of Tires when I call the update method?

Is Car the name of your context object, or is it just one of your models? — pquest, Dec 10 '14 at 16:53
Where does the tire object come from? If you got it from the database it should work. — Stilgar, Dec 10 '14 at 17:01
What is the Car object? Is it your DbContext? If your Car is an Entity then SaveChanges should really live on the context. — BenjaminPaul, Dec 10 '14 at 17:02

ilay zeidman test · Answer 1 · 2014-12-10T17:16:55.650

0

You need to find the tire in the database and then remove it:

var tire=context.Tires.Where(t=>t.Name==tireName).Single();
Car.Tires.Remove(tire);
context.SaveChanges();

edited Dec 10 '14 at 17:16

answered Dec 10 '14 at 16:56

ilay zeidman test

17
2

what the hell. On Nhibernate I simple call Car.SaveOrUpdate() and then the list of tires get updated without needing to calculate what tire was removed. – alansiqueira27 Dec 10 '14 at 16:59
Do not use .First() when you mean .Single() – Stilgar Dec 10 '14 at 17:00
In entityframework it is not working like that look at this maybe it will give you direction: http://stackoverflow.com/questions/9606866/cannot-get-relationship-to-update-for-navigation-properties-in-entity-framework – ilay zeidman test Dec 10 '14 at 17:05
1

look at BenjaminPaul answer this is what I meant, it is more detailed! – ilay zeidman test Dec 10 '14 at 17:18

BenjaminPaul · Answer 2 · 2014-12-10T17:20:01.520

Firstly, there is something a little strange about the way you have things setup... without a little more code it's hard to work out what you are doing but here is what I would expect if I was to do this myself with Entity Framework.

Firstly... you need a DbContext, your context would look something like this...

public class SomeContext : DbContext
{
    public DbSet<Car> Cars { get; set; }
    public DbSet<Tyre> Tires { get; set; }
}

Then some pocos...

public class Car {
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual List<Tyre> Tires { get; set; }
}

public class Tyre {
    public virtual int Id { get; set; }

    // More properties...

    [ForeignKey("CarId")]
    public virtual int CarId { get; set; }
    public virtual Car Car { get; set; }
}

Then I would expect you to do something like this.... my brain is not working quite the same after a long day but essentially.. remove the tire you no longer need from the Car object you loaded from the database then save your changes.

using (var context = new SomeContext())
{
    var car = context.Cars.Find(carId);
    var tyre = car.Tires.Single(t => t.Id == tireId);
    car.Tires.Remove(tyre);

    context.SaveChanges();
}

Hope this helps.

that's what I am already doing, but I'm not using code-first. It still not working =/ — alansiqueira27, Dec 10 '14 at 17:52

How to Detect Change on 1-N

2 Answers2