将关联从has_many转换为has_one

Question

I have two related models TripPlan and Place.

class TripPlan < ActiveRecord::Base
  has_many :places
end

class Place < ActiveRecord::Base
  belongs_to :trip_plan
end

There's a corresponding migration for the places table:

class CreatePlaces < ActiveRecord::Migration
  def change
    create_table :places do |t|
      t.references :trip_plan, index: true

      t.timestamps null: false
    end
  end
end

So each TripPlan can have several places and each Place belongs to a single trip plan. But now I need a has_one / belongs_to relation between these models. I modified TripPlan model as follows:

class TripPlan < ActiveRecord::Base
  has_one :place
end

But now if I try TripPlan.find(1).place.build it throws an error:

undefined method 'build' for nil:NilClass

Answer 1

The methods you get with has_one are different

TripPlan.find(1).build_place

You'll also get the create_place method