EF - Saving a new entity with linked existing entities creating duplicates

public class Car {
    public string SomeProperty { get; set; }
    public Manufacturer Manufacturer { get; set; }
    public IList<Color> Colors { get; set; }
}

public class Manufacturer { 
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Color { 
    public int Id { get; set; }
    public string Name { get; set; }
}

I already have tables full of Colors and Manufacturers. When I create a new car I want to be able to assign it a Color and Manufacturer bound from .net MVC.

When I save my new car with

context.Cars.Add(car);

A new Car is created (great) but a new Color and Manufacturer are also created even though these objects already had an Id and Name set that matched the content in the database.

The two solutions I see are to either write a custom save method for car, and tell the context that the Manufacturer and Color are Unchanged.

context.Cars.Add(car);
context.Entry(car.Manufacturer).State = EntityState.Unchanged;
foreach (Color color in car.Colors)
   context.Entry(car.Color).State = EntityState.Unchanged;

Alternatively, to load the Manufacturer and Color from EF and then link them to the Car, instead of using the MVC bound objects.

car.Manufacturer = carRepository.GetManufacturer(car.Manufacturer.Id);
car.Colors = carRepository.GetColorsById(car.Colors);

I am not thrilled by either solution as this example is very trivial, but my real cases are far more complicated. I don't really want to have to fiddle around with EF in detail for each object I save. I have lots of complex object graphs to save and this seems very error prone.

Is there a way of making EF behave more like NHibernate, whereby you can give it something 开发者_运维技巧with an ID already assigned and it will assume without your intervention that it already exists?

Edit - question clarified to show collection of existing entities as well as many-to-one relationships.

Unfortunately, EF does not have anything like session.Load in NHibernate that allows you to get a proxy from an id.

The usual way to deal with this in EF is create a separate FK field containing the scalar value that corresponds to the reference. For example:

public virtual Manufacturer Manufacturer { get; set; }
public int ManufacturerId { get; set; }

Then you only have to set ManufacturerId and it will be saved correctly.

(So much for "POCO" and "code first". Pffffff)

You can define scalar properties in your entities and bind the values to them instead. Eg add ManufacturerId and ColorId

public class Car {
    public string SomeProperty { get; set; }
    public int? ManufacturerId { get; set; }
    public virtual Manufacturer Manufacturer { get; set; }
    public int? ColorId { get; set; }
    public virtual Color Color { get; set; }
}

Then set those scalar properties when you assign (eg through a DropDownList)

This way you can avoid loading many related entities to populate the entity.