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.
# File activerecord/lib/active_record/core.rb, line 382 def ==(comparison_object) super || comparison_object.instance_of?(self.class) && !id.nil? && comparison_object.id == id end