How to test for (ActiveRecord) object equality

Question

In Ruby 1.9.2 on Rails 3.0.3, I'm attempting to test for object equality between two Friend (class inherits from ActiveRecord::Base) objects.

The objects are equal, but the test fails:

Failure/Error: Friend.new(name: 'Bob').should eql(Friend.new(name: 'Bob'))  expected #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil>      got #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil>  (compared using eql?) 

Just for grins, I also test for object identity, which fails as I'd expect:

Failure/Error: Friend.new(name: 'Bob').should equal(Friend.new(name: 'Bob'))  expected #<Friend:2190028040> => #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil>      got #<Friend:2190195380> => #<Friend id: nil, event_id: nil, name: 'Bob', created_at: nil, updated_at: nil>  Compared using equal?, which compares object identity, but expected and actual are not the same object. Use 'actual.should == expected' if you don't care about object identity in this example. 

Can someone explain to me why the first test for object equality fails, and how I can successfully assert those two objects are equal?

Answer 1

Rails deliberately delegates equality checks to the identity column. If you want to know if two AR objects contain the same stuff, compare the result of calling #attributes on both.

Answer 2

Take a look at the API docs on the == (alias eql?) operation for ActiveRecord::Base

Returns true if comparison_object is the same exact object, or comparison_object is of the same type and self has an ID and it is equal to comparison_object.id.

Note that new records are different from any other record by definition, unless the other record is the receiver itself. Besides, if you fetch existing records with select and leave the ID out, you’re on your own, this predicate will return false.

Note also that destroying a record preserves its ID in the model instance, so deleted models are still comparable.