Why am I unable to save an existing user with updated attributes in my rails app?

Question

I ran this in a rails console:

u = User.first
  User Load (0.3ms)  SELECT "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT 1
 => #<User id: 4, name: "Administrator", email: "administrator@wdis.com", created_at: "2013-09-27 01:01:54", updated_at: "2013-09-29 23:52:11", password_digest: ".......", remember_token: "........", admin: true, num_credits: nil> 
2.0.0p247 :002 > u.num_credits = 1
 => 1 
2.0.0p247 :003 > u.num_credits
 => 1 
2.0.0p247 :004 > u.save
   (0.3ms)  begin transaction
  User Exists (0.3ms)  SELECT 1 AS one FROM "users" WHERE (LOWER("users"."email") = LOWER('administrator@wdis.com') AND "users"."id" != 4) LIMIT 1
   (0.2ms)  rollback transaction
 => false 

Answer 1

There must be some validation which is stopping this user to be saved. Just check your validations in User model. You can also check the errors on this user using u.errors.full_messages.to_sentence