Simple Delete in Entity Framework using WCF (many to many relationship) - wcf

Question

I have a simple database model containing 3 Tables : Companies, Categories and CompanyCategories (which is a relation table with only 2 FK : CompanyID and CategoryID).
My edmx model it only shows Companies and Categories tables (CompanyCategories is somehow hidded since its a simple many to many relationship table).
In the WCF service, I have a GetDatabase() function that returns all the database objets wrapped in one big custom object :
[OperationContract]
public FullDatabase GetDatabase()
{
DBEntities context = new DBEntities ();
FullDatabase mydb = new FullDatabase();
mydb.Companies = context.Companies.ToList();
mydb.Categories = context.Categories.ToList();
return mydb;
}
[OperationContract]
public FullDatabase UpdateDatabase(FullDatabase db)
{
// Here is my problem when removing a category from a company on
// the client its been brought back in my db object
}
class FullDatabase()
{
List<Company> Companies;
List<Category> Categories;
}
On the client now, I use GetDatabaseAsync() to retrieve the database in a _FullDB variable. Now using that variable I tried the following :
// Adding a category like that Works well
Company c = _FullDB.Companies.First();
c.Categories.Add(_FullDB.Categories.First());
wcfServiceClientObject.UpdateDatabaseASync(_FullDB);
.....
// Removing a category, doesn't work though :
Company c = _FullDB.Companies.First();
c.Categories.Remove(_FullDB.Categories.First());
wcfServiceClientObject.UpdateDatabaseASync(_FullDB);
// here my c.Categories.Count is updated correctly to delete the item
// but when on the server after (in the UpdateDatabase function) the item
// I deleted is still there
I really dont understand why the Add would work but not the Remove.

Answer 1

Finally found the problem. Now it works, but I'm not sure it is the best way to do it.
When removing the category from the company, I also had to also remove the company from the category...
Company comp = _FullDB.Companies.First();
Category cat = _FullDB.Categories.First();
comp.Categories.Remove(cat);
cat.Companies.Remove(comp);
wcfServiceClientObject.UpdateDatabaseASync(_FullDB);