RSpec: Factory definition for associated object - ruby-on-rails

Question

I have the following three models: Product, Warehouse and Inventory
# app/models/product.rb
class Product < ApplicationRecord
has_many :inventories
has_many :warehouses, through: :inventories
end
# app/models/warehouse.rb
class Warehouse < ApplicationRecord
has_many :inventories
has_many :products, through: :inventories
end
# app/models/inventory.rb
class Inventory < ApplicationRecord
belongs_to :product
belongs_to :warehouse
end
I have this factory for Inventory:
FactoryBot.define do
factory :inventory do
product { nil }
warehouse { nil }
item_count { 1 }
low_item_threshold { 1 }
end
end
How can I use this factory for Inventory or what changes are needed in my other factories so that I can have a spec something like this?
RSpec.describe Inventory, type: :model do
it "has a valid factory" do
expect(FactoryBot.build(:inventory)).to be_valid
end
end

Answer 1

What you need is to change the :inventory factory definition, like this
FactoryBot.define do
factory :inventory do
product
warehouse
item_count { 1 }
low_item_threshold { 1 }
end
end
This will "tell" factory bot to instantiate the associated objects (https://github.com/thoughtbot/factory_bot/blob/master/GETTING_STARTED.md#associations)
But for this to work, you need to define warehouse and product factories.

Answer 2

You can use either the create or build methods passing the name if the factory as a symbol:
it "has a valid factory" do
expect(create(:inventory)).to be_valid
end
# OR
it "has a valid factory" do
expect(build(:inventory)).to be_valid
end
create will save the model while build will simply instantiate it. If you are having trouble getting your factories loaded, ensure they are in the right place.

Answer 3

you might change definition of the class Inventory to:
# app/models/inventory.rb
class Inventory < ApplicationRecord
belongs_to :product, optional: true
belongs_to :warehouse, optional: true
end
and you will get successful validation
inventory = FactoryBot.build(:inventory)
inventory.valid? #true
###############################################
Explanation:
to build valid Inventory object with current definition(like in question description) of the model its necessary to initialize associated objects also. So every time validation checks if warehouse and product attributes present.
But its possible to avoid such behaviour with associations attribute optional: true.
# app/models/inventory.rb
class Inventory < ApplicationRecord
belongs_to :product
belongs_to :warehouse
end
FactoryBot.define do
factory :inventory do
product { nil }
warehouse { nil }
item_count { 1 }
low_item_threshold { 1 }
end
end
inventory = FactoryBot.build(:inventory)
inventory.valid? #false
inventory.errors.full_messages # ["Product must exist", "Warehouse must exist"]
:required
When set to true, the association will also have its
presence validated. This will validate the association itself, not the
id. You can use :inverse_of to avoid an extra query during validation.
NOTE: required is set to true by default and is deprecated. If you
don’t want to have association presence validated, use optional: true.
https://apidock.com/rails/ActiveRecord/Associations/ClassMethods/belongs_to