Entity Framework 4.1

Quick Tip: Add/Attach returns your entity

We did a few things in EF 4.1 that were not at all ground-breaking or cool or anything like that, but were intended only to make programming a little bit more pleasant. One of those was making the Add and Attach methods return a reference to the added or attached entity.

This is nice because it can sometimes save a local variable or a line or two of code and thereby make your code easier to read.>  For example, in a little test app I was just working on I wanted to create a new “Doc” entity, add it to the context, then use it later in the same method.>  Instead of writing:

var doc = new Doc();

I was able to write this:

var doc = context.Docs.Add(new Doc());

Another advantage of returning the added entity is that it allows the Add/Attach methods to be more composeable. For example, later in the same method I had some code that attempted to find an entity in the context and, if the entity was not found, created a new one and added that new entity to the context. Instead of writing:

var word = context.ChangeTracker.Entries<Word>()
                                .Select(e => e.Entity)
                                .SingleOrDefault(w => w.TheWord == theWord);
if (word == null)
    word = new Word { TheWord = theWord };

I was able to use a more functional approach:

var word = context.ChangeTracker.Entries<Word>()
                                .Select(e => e.Entity)
                                .SingleOrDefault(w => w.TheWord == theWord)
    ?? context.Words.Add(new Word { TheWord = theWord });

Hopefully once in a while you can use the return value from Add or Attach and be just a little bit happier because of it. :-)

This page is up-to-date as of April 19th, 2011. Some things change. Some things stay the same. Use your noggin.