Error: Unknown attribute in ActiveRecord(ruby). How to fix?

Hello.

There are the following models:

class Contractor < User
 has_many :contractorEs
 has_many :customers
end

class Customer < User
 belongs_to :contractor
 has_many :customerEs
end

There is a migration:

class AddContractorIdToCustomers < ActiveRecord::Migration
 def change
 add_column :customers, :contractor_id, :integer
end
end

Try to create customer (Customer), for this I go to the console and do the following:

c = Contractor.first
c.customers.build

Is created the customer will receive the following error message:

ActiveRecord::UnknownAttributeError: unknown attribute: contractor_id

The migration ran, the server will have restartovat. Problem unfortunately remains.
Tell me, please, what it can be connected and how to fix it.

The rays of goodness to you :)

UPD: Ruby 2/Rails 4
UPD 2: I use STI, all inherited from User-a. Maybe the problem is related to this?
UPD 3: Continue to investigate the problem. It turned out that the model is created through the Customer.new in the boxes no contractor_id:

<customer id: nil, first_name: last_name: address: country: zip: city: phone: company_name: signature: type: "customer", created_at: updated_at: v_token: password_digest: u_token: email: state: "new">
</customer>

If Customer I will inherit from ActiveRecord::Base, everything works fine. But I need to inherit from User.