Update relationships when saving changes of EF4 POCO objects

Question

Entity Framework 4, POCO objects and ASP.Net MVC2. I have a many to many relationship, lets say between BlogPost and Tag entities. This means that in my T4 generated POCO Bl

Answer 1

I know it's late for the OP but since this is a very common issue I posted this in case it serves someone else. I've been toying around with this issue and I think I got a fairly simple solution, what I do is:

1. Save main object (Blogs for example) by setting its state to Modified.
2. Query the database for the updated object including the collections I need to update.
3. Query and convert .ToList() the entities I want my collection to include.
4. Update the main object's collection(s) to the List I got from step 3.
5. SaveChanges();

In the following example "dataobj" and "_categories" are the parameters received by my controller "dataobj" is my main object, and "_categories" is an IEnumerable containing the IDs of the categories the user selected in the view.

    db.Entry(dataobj).State = EntityState.Modified;
    db.SaveChanges();
    dataobj = db.ServiceTypes.Include(x => x.Categories).Single(x => x.Id == dataobj.Id);
    var it = _categories != null ? db.Categories.Where(x => _categories.Contains(x.Id)).ToList() : null;
    dataobj.Categories = it;
    db.SaveChanges();

It even works for multiple relations