Adding reference with different model name in Rails 5

In the scenario where you want to add a reference on a model and the reference is named different than the model, do the following:

rails generate migration Add<Reference Name>To<Target Model> <Reference name>:references

e.g.

rails generate migration AddCreatorToOrders creator:references

Then edit the created migration to be the following:

class AddCreatorToOrders < ActiveRecord::Migration[5.2]
  def change
    add_reference :orders, :creator, foreign_key: { to_table: :users }
  end
end

The important bit here is changing foreign_key: true to foreign_key: { to_table: :users }.

Finally you also need to specify the relationship correctly on the model:

belongs_to :creator, class_name: 'User'

Hope it helps :)