Support composite foreign keys (#126)

This PR adds support for composite foreign keys. Credit goes to @carldr
for ctran/annotate_models#1013.

Closes #121.

lib/annotate_rb/model_annotator/foreign_key_annotation/annotation_builder.rb

@@ -23,14 +23,19 @@ def build
           return "" if foreign_keys.empty?
 
           format_name = lambda do |fk|
-            return fk.options[:column] if fk.name.blank?
+            return fk.column if fk.name.blank?
 
             @options[:show_complete_foreign_keys] ? fk.name : fk.name.gsub(/(?<=^fk_rails_)[0-9a-f]{10}$/, "...")
           end
 
           max_size = foreign_keys.map(&format_name).map(&:size).max + 1
-          foreign_keys.sort_by { |fk| [format_name.call(fk), fk.column] }.each do |fk|
-            ref_info = "#{fk.column} => #{fk.to_table}.#{fk.primary_key}"
+          foreign_keys.sort_by { |fk| [format_name.call(fk), stringify_columns(fk.column)] }.each do |fk|
+            ref_info = if fk.column.is_a?(Array) # Composite foreign key using multiple columns
+              "#{stringify_columns(fk.column)} => #{fk.to_table}#{stringify_columns(fk.primary_key)}"
+            else
+              "#{fk.column} => #{fk.to_table}.#{fk.primary_key}"
+            end
+
             constraints_info = ""
             constraints_info += "ON DELETE => #{fk.on_delete} " if fk.on_delete
             constraints_info += "ON UPDATE => #{fk.on_update} " if fk.on_update
@@ -51,6 +56,13 @@ def build
 
           fk_info
         end
+
+        private
+
+        # The fk columns might be composite keys, so format them into a string for the annotation
+        def stringify_columns(columns)
+          columns.is_a?(Array) ? "[#{columns.join(", ")}]" : columns
+        end
       end
     end
   end

spec/lib/annotate_rb/model_annotator/foreign_key_annotation/annotation_builder_spec.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+RSpec.describe AnnotateRb::ModelAnnotator::ForeignKeyAnnotation::AnnotationBuilder do
+  include AnnotateTestHelpers
+
+  describe "#build" do
+    subject { described_class.new(model, options).build }
+
+    let(:model) do
+      klass = begin
+        primary_key = nil
+        columns = []
+        indexes = []
+
+        mock_class(
+          :users,
+          primary_key,
+          columns,
+          indexes,
+          foreign_keys
+        )
+      end
+
+      ::AnnotateRb::ModelAnnotator::ModelWrapper.new(klass, options)
+    end
+    let(:options) { ::AnnotateRb::Options.new({show_complete_foreign_keys: true}) }
+
+    context "without foreign keys" do
+      let(:foreign_keys) { [] }
+
+      it { is_expected.to be_blank }
+    end
+
+    context "with foreign keys" do
+      let(:foreign_keys) do
+        [
+          mock_foreign_key("fk_rails_cf2568e89e", "foreign_thing_id", "foreign_things"),
+          mock_foreign_key("custom_fk_name", "other_thing_id", "other_things"),
+          mock_foreign_key("fk_rails_a70234b26c", "third_thing_id", "third_things")
+        ]
+      end
+      let(:expected_output) do
+        <<~OUTPUT
+          #
+          # Foreign Keys
+          #
+          #  custom_fk_name       (other_thing_id => other_things.id)
+          #  fk_rails_a70234b26c  (third_thing_id => third_things.id)
+          #  fk_rails_cf2568e89e  (foreign_thing_id => foreign_things.id)
+        OUTPUT
+      end
+
+      it { is_expected.to eq(expected_output) }
+    end
+
+    context "with a composite foreign key" do
+      let(:foreign_keys) do
+        [
+          mock_foreign_key("fk_rails_cf2568e89e", "foreign_thing_id", "foreign_things"),
+          mock_foreign_key("custom_fk_name", ["tenant_id", "customer_id"], "customers", ["tenant_id", "id"])
+        ]
+      end
+      let(:expected_output) do
+        <<~OUTPUT
+          #
+          # Foreign Keys
+          #
+          #  custom_fk_name       ([tenant_id, customer_id] => customers[tenant_id, id])
+          #  fk_rails_cf2568e89e  (foreign_thing_id => foreign_things.id)
+        OUTPUT
+      end
+
+      it { is_expected.to eq(expected_output) }
+    end
+  end
+end