How to update entities which are modified outside the DbContext?

Question

I\'ve a small problem with updating entities if the entity is changed outside the DbContext (is a detached entity). If I attach the modified entity, it\'s state is not modif

Answer 1

If you use the Attach approach on an entity which has already changed, you will also need to tell EF that the entity is modified, after attaching it.

context.Specifications.Attach(entity);
context.Entry(entity).State = EntityState.Modified;
context.SaveChanges();

An alternative is to fetch (with tracking), then update the fields, and save:

var entity = context.Specifications.First(s => s.Id == 1234);
entity.Name = "Foo";
... other changes here
context.SaveChanges();

Another option is to make the changes to the entity after you have reattached it, e.g. as per here

context.Specifications.Attach(entity);
entity.Name = "Foo";
... other changes here
context.SaveChanges();

Edit

You can use generics with DbSet - either class, or method - as follows:

public void Update<TEntity>(TEntity entity)
{
    DbContext.Set<TEntity>().Attach(entity);
    DbContext.Entry(entity).State = EntityState.Modified;
    DbContext.SaveChanges();
 }

Edit : For updating of detached Parent / Child Graphs

For updating of simple / shallow parent-child relationships where efficiency and performance is not important, simply deleting all old children and reinserting the new ones is an easy (although ugly) solution.

However, for a more efficient scenario requires us to traverse the graph, detect changes, and then add newly inserted, update existing, ignore unchanged, and delete removed items from the Context.

Slauma shows a great example of this here.

You might want to look at using GraphDiff, which can do all this leg work for you!