Reflection for attachments

Add the ability to reflect on the attachments that have been defined using ActiveRecord::Reflection.

activerecord/lib/active_record/reflection.rb

@@ -11,27 +11,33 @@ module ActiveRecord
     included do
       class_attribute :_reflections, instance_writer: false, default: {}
       class_attribute :aggregate_reflections, instance_writer: false, default: {}
+      class_attribute :attachment_reflections, instance_writer: false, default: {}
     end
 
     def self.create(macro, name, scope, options, ar)
-      klass = \
-        case macro
-        when :composed_of
-          AggregateReflection
-        when :has_many
-          HasManyReflection
-        when :has_one
-          HasOneReflection
-        when :belongs_to
-          BelongsToReflection
-        else
-          raise "Unsupported Macro: #{macro}"
-        end
-
-      reflection = klass.new(name, scope, options, ar)
+      reflection = reflection_class_for(macro).new(name, scope, options, ar)
       options[:through] ? ThroughReflection.new(reflection) : reflection
     end
 
+    def self.reflection_class_for(macro)
+      case macro
+      when :composed_of
+        AggregateReflection
+      when :has_many
+        HasManyReflection
+      when :has_one
+        HasOneReflection
+      when :belongs_to
+        BelongsToReflection
+      when :has_one_attached
+        HasOneAttachedReflection
+      when :has_many_attached
+        HasManyAttachedReflection
+      else
+        raise "Unsupported Macro: #{macro}"
+      end
+    end
+
     def self.add_reflection(ar, name, reflection)
       ar.clear_reflections_cache
       name = name.to_s
@@ -42,14 +48,18 @@ module ActiveRecord
       ar.aggregate_reflections = ar.aggregate_reflections.merge(name.to_s => reflection)
     end
 
+    def self.add_attachment_reflection(ar, name, reflection)
+      ar.attachment_reflections.merge!(name.to_s => reflection)
+    end
+
     # \Reflection enables the ability to examine the associations and aggregations of
     # Active Record classes and objects. This information, for example,
     # can be used in a form builder that takes an Active Record object
     # and creates input fields for all of the attributes depending on their type
     # and displays the associations to other objects.
     #
-    # MacroReflection class has info for AggregateReflection and AssociationReflection
-    # classes.
+    # MacroReflection class has info for the AggregateReflection and
+    # AssociationReflection classes.
     module ClassMethods
       # Returns an array of AggregateReflection objects for all the aggregations in the class.
       def reflect_on_all_aggregations
@@ -64,6 +74,21 @@ module ActiveRecord
         aggregate_reflections[aggregation.to_s]
       end
 
+      # Returns an array of reflection objects for all the attachments in the
+      # class.
+      def reflect_on_all_attachments
+        attachment_reflections.values
+      end
+
+      # Returns the reflection object for the named +attachment+.
+      #
+      #    User.reflect_on_attachment(:avatar)
+      #    # => the avatar reflection
+      #
+      def reflect_on_attachment(attachment)
+        attachment_reflections[attachment.to_s]
+      end
+
       # Returns a Hash of name of the reflection as the key and an AssociationReflection as the value.
       #
       #   Account.reflections # => {"balance" => AggregateReflection}
@@ -136,6 +161,8 @@ module ActiveRecord
     #         HasOneReflection
     #         BelongsToReflection
     #         HasAndBelongsToManyReflection
+    #       HasOneAttachedReflection
+    #       HasManyAttachedReflection
     #     ThroughReflection
     #     PolymorphicReflection
     #     RuntimeReflection
@@ -412,6 +439,22 @@ module ActiveRecord
       end
     end
 
+    # Holds all the metadata about a has_one_attached attachment as it was
+    # specified in the Active Record class.
+    class HasOneAttachedReflection < MacroReflection #:nodoc:
+      def macro
+        :has_one_attached
+      end
+    end
+
+    # Holds all the metadata about a has_many_attached attachment as it was
+    # specified in the Active Record class.
+    class HasManyAttachedReflection < MacroReflection #:nodoc:
+      def macro
+        :has_many_attached
+      end
+    end
+
     # Holds all the metadata about an association as it was specified in the
     # Active Record class.
     class AssociationReflection < MacroReflection #:nodoc:

activestorage/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Add the ability to reflect on defined attachments using the existing
+    ActiveRecord reflection mechanism.
+
+    *Kevin Deisz*
+
 *   Variant arguments of `false` or `nil` will no longer be passed to the
     processor. For example, the following will not have the monochrome
     variation applied:

activestorage/lib/active_storage/attached/macros.rb

@@ -48,6 +48,12 @@ module ActiveStorage
       else
         before_destroy { public_send(name).detach }
       end
+
+      ActiveRecord::Reflection.add_attachment_reflection(
+        self,
+        name,
+        ActiveRecord::Reflection.create(:has_one_attached, name, nil, { dependent: dependent }, self)
+      )
     end
 
     # Specifies the relation between multiple attachments and the model.
@@ -105,6 +111,12 @@ module ActiveStorage
       else
         before_destroy { public_send(name).detach }
       end
+
+      ActiveRecord::Reflection.add_attachment_reflection(
+        self,
+        name,
+        ActiveRecord::Reflection.create(:has_many_attached, name, nil, { dependent: dependent }, self)
+      )
     end
   end
 end

activestorage/test/models/reflection_test.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class ActiveStorage::ReflectionTest < ActiveSupport::TestCase
+  test "allows reflecting for all attachment" do
+    expected_classes =
+      User.reflect_on_all_attachments.all? do |reflection|
+        reflection.is_a?(ActiveRecord::Reflection::HasOneAttachedReflection) ||
+          reflection.is_a?(ActiveRecord::Reflection::HasManyAttachedReflection)
+      end
+
+    assert expected_classes
+  end
+
+  test "allows reflecting on a singular has_one_attached attachment" do
+    reflection = User.reflect_on_attachment(:avatar)
+
+    assert_equal :avatar, reflection.name
+    assert_equal :has_one_attached, reflection.macro
+  end
+
+  test "allows reflecting on a singular has_many_attached attachment" do
+    reflection = User.reflect_on_attachment(:highlights)
+
+    assert_equal :highlights, reflection.name
+    assert_equal :has_many_attached, reflection.macro
+  end
+end