Add ingredient associations

An ingredient association is a way to be able to eager load
associated records of essence classes. The EssencePicture for example
`belongs_to :picture`.

In able to eager load we create an `belongs_to :ingredient_association`
for you and add an ActiveRecord hack that skips eager loading on records
not having such relation.

That way we can load a page and include all elements, their contents,
essences and their associated records as well.

This should speed up admin pages with large element lists and API calls
to pages with many elements a lot.

app/models/alchemy/essence_page.rb

@@ -6,11 +6,15 @@ class EssencePage < BaseRecord
 
     acts_as_essence(
       ingredient_column: :page,
-      preview_text_method: :name
+      preview_text_method: :name,
+      belongs_to: {
+        class_name: 'Alchemy::Page',
+        foreign_key: :page_id,
+        inverse_of: :essence_pages,
+        optional: true
+      }
     )
 
-    belongs_to :page, class_name: 'Alchemy::Page', optional: true
-
     def ingredient=(page)
       case page
       when PAGE_ID

app/models/alchemy/essence_picture.rb

@@ -25,9 +25,13 @@
 
 module Alchemy
   class EssencePicture < BaseRecord
-    acts_as_essence ingredient_column: 'picture'
+    acts_as_essence ingredient_column: :picture, belongs_to: {
+      class_name: 'Alchemy::Picture',
+      foreign_key: :picture_id,
+      inverse_of: :essence_pictures,
+      optional: true
+    }
 
-    belongs_to :picture, optional: true
     delegate :image_file_width, :image_file_height, :image_file, to: :picture
     before_save :fix_crop_values
     before_save :replace_newlines

app/models/alchemy/picture.rb

@@ -30,7 +30,11 @@ class Picture < BaseRecord
     include Alchemy::Picture::Transformations
     include Alchemy::Picture::Url
 
-    has_many :essence_pictures, class_name: 'Alchemy::EssencePicture', foreign_key: 'picture_id'
+    has_many :essence_pictures,
+      class_name: 'Alchemy::EssencePicture',
+      foreign_key: 'picture_id',
+      inverse_of: :ingredient_association
+
     has_many :contents, through: :essence_pictures
     has_many :elements, through: :contents
     has_many :pages, through: :elements

lib/alchemy/essence.rb

@@ -3,6 +3,18 @@
 require 'active_record'
 
 module Alchemy #:nodoc:
+  # A bogus association that skips eager loading for essences not having an ingredient association
+  class IngredientAssociation < ActiveRecord::Associations::BelongsToAssociation
+    # Skip eager loading if called by Rails' preloader
+    def klass
+      if caller.any? { |line| line =~ /preloader\.rb/ }
+        nil
+      else
+        super
+      end
+    end
+  end
+
   module Essence #:nodoc:
     def self.included(base)
       base.extend(ClassMethods)
@@ -31,6 +43,8 @@ def acts_as_essence(options = {})
           ingredient_column: 'body'
         }.update(options)
 
+        @_classes_with_ingredient_association ||= []
+
         class_eval <<-RUBY, __FILE__, __LINE__ + 1
           attr_writer :validation_errors
           include Alchemy::Essence::InstanceMethods
@@ -66,8 +80,31 @@ def preview_text_column
             '#{configuration[:preview_text_column] || configuration[:ingredient_column]}'
           end
         RUBY
+
+        if configuration[:belongs_to]
+          class_eval <<-RUBY, __FILE__, __LINE__ + 1
+            belongs_to :ingredient_association, #{configuration[:belongs_to]}
+
+            alias_method :#{configuration[:ingredient_column]}, :ingredient_association
+            alias_method :#{configuration[:ingredient_column]}=, :ingredient_association=
+          RUBY
+
+          @_classes_with_ingredient_association << self
+        end
       end
 
+      # Overwrite ActiveRecords method to return a bogus association class that skips eager loading
+      # for essence classes that do not have an ingredient association
+      def _reflect_on_association(name)
+        if name == :ingredient_association && !in?(@_classes_with_ingredient_association)
+          OpenStruct.new(association_class: Alchemy::IngredientAssociation)
+        else
+          super
+        end
+      end
+
+      private
+
       # Register the current class as has_many association on +Alchemy::Page+ and +Alchemy::Element+ models
       def register_as_essence_association!
         klass_name = model_name.to_s
@@ -231,4 +268,5 @@ def has_tinymce?
     end
   end
 end
-ActiveRecord::Base.class_eval { include Alchemy::Essence } if defined?(Alchemy::Essence)
+
+ActiveRecord::Base.include(Alchemy::Essence)

lib/alchemy/test_support/essence_shared_examples.rb

@@ -10,6 +10,18 @@
   let(:content) { Alchemy::Content.new(name: 'foo') }
   let(:content_definition) { {'name' => 'foo'} }
 
+  describe 'eager loading' do
+    before do
+      2.times { described_class.create! }
+    end
+
+    it 'does not throw error if eager loaded' do
+      expect {
+        described_class.all.includes(:ingredient_association).to_a
+      }.to_not raise_error
+    end
+  end
+
   it "touches the content after update" do
     element = FactoryBot.create(:alchemy_element)
     content = FactoryBot.create(:alchemy_content, element: element, essence: essence, essence_type: essence.class.name)

spec/models/alchemy/essence_page_spec.rb

@@ -10,6 +10,15 @@
     let(:ingredient_value) { page }
   end
 
+  describe 'eager loading' do
+    let!(:essence_pages) { create_list(:alchemy_essence_page, 2) }
+
+    it 'eager loads pages' do
+      essences = described_class.all.includes(:ingredient_association)
+      expect(essences[0].association(:ingredient_association)).to be_loaded
+    end
+  end
+
   describe 'ingredient=' do
     subject(:ingredient) { essence.page }
 

spec/models/alchemy/essence_picture_spec.rb

@@ -9,6 +9,15 @@ module Alchemy
       let(:ingredient_value) { Picture.new }
     end
 
+    describe 'eager loading' do
+      let!(:essence_pictures) { create_list(:alchemy_essence_picture, 2) }
+
+      it 'eager loads pictures' do
+        essences = described_class.all.includes(:ingredient_association)
+        expect(essences[0].association(:ingredient_association)).to be_loaded
+      end
+    end
+
     it_behaves_like "has image transformations" do
       let(:picture) { build_stubbed(:alchemy_essence_picture) }
     end