Linq update many-many relationship

New to Linq to Entities. I am using entity framework and linq. In my db I have something akin to Cars, Users, UserCars where UserCars holds the ID from User and Cars. Standard stuff.

EF maps this to Car and User objects.

Now a user currently has many cars. Through my application I end up with a new List of Car IDs.

I need to update the UserCars table with the new list of cars for the current user.

So what needs to happen basically开发者_如何学JAVA, The current cars for the user are deleted, and the new list of car ids/userid is inserted.

What is the easiest way to go about this using linq to entities?

The User entity should have a Cars property. You can just clear that collection and then add the new Cars to reflect the new state, i.e. somewhat like this:

User myUser = context.Users.First();
var carCollection = context.Cars.Where( c => carIdCollection.Contains(c.Id));
myUser.Cars.Clear();

foreach(Car car in carCollection)
   myUser.Cars.Add(car);

...
context.SaveChanges();

You could use a generic method which can handle what ever type you pass it:

Protected Sub UpdateManyToMany(Of T As Class)(database as SomeEntities, collection As ICollection(Of T), idList As List(Of Integer))
'update a many to many collection given a list of key IDs
  collection.Clear()
  Dim source = database.Set(Of T)()

  If idList IsNot Nothing Then
    For Each i As Integer In idList
      Dim record = source.Find(i)
      collection.Add(record)
    Next
  End If
End Sub