When we compare two Active Record objects, we are comparing their ids.

active_record_object_hash.rb

[1] pry(main)> p1 = Post.first
  Post Load (0.2ms)  SELECT "posts".* FROM "posts" LIMIT 1
=> #<Post id: 4, title: "Hello", content: "World.", created_at: "2012-05-20 08:38:46", updated_at: "2012-05-20 08:38:46">
[2] pry(main)> p2 = Post.first
  Post Load (0.2ms)  SELECT "posts".* FROM "posts" LIMIT 1
=> #<Post id: 4, title: "Hello", content: "World.", created_at: "2012-05-20 08:38:46", updated_at: "2012-05-20 08:38:46">
[3] pry(main)> p1 == p2
=> true
[4] pry(main)> p1.title = "hi"
=> "hi"
[5] pry(main)> p1 == p2
=> true
[6] pry(main)> p1.hash == p2.hash
=> true
[7] pry(main)> p1.hash
=> -2154204912980276923
[8] pry(main)> p1.id.hash
=> -2154204912980276923

Yay Ruby!!