Question

I have defined three classes:

class Animal < ActiveRecord::Base
end

class Cat < Animal
  has_many :toys
end

class Toy
  validates_presence_of :cat
  belongs_to :cat
end

When I create a toy that should belong to a cat with :
Cat.first.toys << Toy.create!(:name => 'Toy 1')

it throws :

ActiveRecord::RecordInvalid: Validation failed: Cat can't be blank

Answer 1

Cat.first.toys << Toy.create!(:name => 'Toy 1')

The sequence of the code would be executed like the following:

tmp_toy = Toy.create!(:name => 'Toy 1')
Cat.first.toys << tmp_toy

So when you are creating the new toy, you did not provide the required cat, that causes the error.

You could use the following:

Cat.first.toys.create!(:name => 'Toy 1')