ModelAttribute: Add `.group_by_class` method

This returns all defined `ModelAttribute`s as a hash of class keys
containing lists of the attributes they contain.

Refs #4401

2 files changed, 28 insertions, 0 deletions

diff --git a/lib/model_attribute.rb b/lib/model_attribute.rb
index 53c0b7a46..78c9168eb 100644
--- a/lib/model_attribute.rb
+++ b/lib/model_attribute.rb
@@ -17,6 +17,10 @@ class ModelAttribute
       .uniq
   end
 
+  def self.group_by_class
+    all.group_by(&:klass)
+  end
+
   def self.methods_by_class(klass)
     all.select do |model_attr|
       model_attr.klass == klass
diff --git a/spec/lib/model_attribute_spec.rb b/spec/lib/model_attribute_spec.rb
index 9e10bf40f..0ca90430f 100644
--- a/spec/lib/model_attribute_spec.rb
+++ b/spec/lib/model_attribute_spec.rb
@@ -30,6 +30,30 @@ RSpec.describe ModelAttribute do
     end
   end
 
+  describe ".group_by_class" do
+    it "returns all ModelAttributes grouped by klass" do
+      ModelAttribute.instance_variable_set(:@__all__, [
+        ModelAttribute.new(:route, :name, :string),
+        ModelAttribute.new(:route, :published_name, :string),
+        ModelAttribute.new(:journey_pattern, :name, :string),
+        ModelAttribute.new(:vehicle_journey, :number, :integer)
+      ])
+
+      expect(ModelAttribute.group_by_class).to eq({
+        route: [
+          ModelAttribute.new(:route, :name, :string),
+          ModelAttribute.new(:route, :published_name, :string),
+        ],
+        journey_pattern: [
+          ModelAttribute.new(:journey_pattern, :name, :string),
+        ],
+        vehicle_journey: [
+          ModelAttribute.new(:vehicle_journey, :number, :integer)
+        ]
+      })
+    end
+  end
+
   describe ".methods_by_class" do
     it "returns all ModelAttributes for a given class" do
       ModelAttribute.instance_variable_set(:@__all__, [