3 files changed, 46 insertions, 0 deletions
diff --git a/activestorage/CHANGELOG.md b/activestorage/CHANGELOG.md
index c8911fe611..4aa551781b 100644
--- a/activestorage/CHANGELOG.md
+++ b/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:
diff --git a/activestorage/lib/active_storage/attached/macros.rb b/activestorage/lib/active_storage/attached/macros.rb
index f99cf35680..6ad9fc43d7 100644
--- a/activestorage/lib/active_storage/attached/macros.rb
+++ b/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
diff --git a/activestorage/test/models/reflection_test.rb b/activestorage/test/models/reflection_test.rb
new file mode 100644
index 0000000000..1ddfafc0f0
--- /dev/null
+++ b/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