Question

According to docs of ActiveRecord::Base:

==(comparison_object) 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.

But my observations show that it only compares instaces, not ids so that following are true:

a = Factory.create(:user)
b = User.find_by_email(a.email) # b is logically same as a

a.id.should == b.id # All good
a.should == b # FAILS: Contradicts the docs
a.should_not == b # Contradicts the docs
a.should_not eql b # Contradicts the docs

The question is 2 AR instances are considered to be different while the docs explicitly say that those should be equal?

UPDATE: The equality DOES work as expected. Code sample above is irrelevant. See my answer below.

Answer 1

Answering my own question (which is irrelevant).

All the equality checks DO work as expected (and described in the docs).
I assume the reason it did not work for me is that I run autotest and something could be cached or some other mythical reason that I can’t explain right now.

To summarise, all the following assertions are indeed passing:

a = Factory.create(:user)
b = User.find_by_email(a.email) # b is logically same as a

a.id.should == b.id
a.should == b
a.should eql b
User.find_by_email(a.email).should == User.find_by_email(a.email)
a.should == User.find_by_email(a.email)
b.should == User.find_by_email(a.email)