fk: make `add_foreign_key` reversible.

3 files changed, 55 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/migration/command_recorder.rb b/activerecord/lib/active_record/migration/command_recorder.rb
index c44d8c1665..bd66c941a2 100644
--- a/activerecord/lib/active_record/migration/command_recorder.rb
+++ b/activerecord/lib/active_record/migration/command_recorder.rb
@@ -74,7 +74,9 @@ module ActiveRecord
         :rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps,
         :change_column_default, :add_reference, :remove_reference, :transaction,
         :drop_join_table, :drop_table, :execute_block, :enable_extension,
-        :change_column, :execute, :remove_columns, :change_column_null # irreversible methods need to be here too
+        :change_column, :execute, :remove_columns, :change_column_null,
+        :add_foreign_key, :remove_foreign_key
+       # irreversible methods need to be here too
       ].each do |method|
         class_eval <<-EOV, __FILE__, __LINE__ + 1
           def #{method}(*args, &block)          # def create_table(*args, &block)
@@ -167,6 +169,19 @@ module ActiveRecord
         [:change_column_null, args]
       end
 
+      def invert_add_foreign_key(args)
+        from_table, _to_table, add_options = *args
+        add_options ||= {}
+
+        if add_options[:name]
+          options = {name: add_options[:name]}
+        elsif add_options[:column]
+          options = {column: add_options[:column]}
+        end
+
+        [:remove_foreign_key, [from_table, options]]
+      end
+
       # Forwards any missing method call to the \target.
       def method_missing(method, *args, &block)
         if @delegate.respond_to?(method)
diff --git a/activerecord/test/cases/migration/command_recorder_test.rb b/activerecord/test/cases/migration/command_recorder_test.rb
index 1c0134843b..64a1b9a84e 100644
--- a/activerecord/test/cases/migration/command_recorder_test.rb
+++ b/activerecord/test/cases/migration/command_recorder_test.rb
@@ -270,6 +270,26 @@ module ActiveRecord
         enable = @recorder.inverse_of :disable_extension, ['uuid-ossp']
         assert_equal [:enable_extension, ['uuid-ossp'], nil], enable
       end
+
+      def test_invert_add_foreign_key_with_column
+        enable = @recorder.inverse_of :add_foreign_key, [:dogs, :people, column: "owner_id"]
+        assert_equal [:remove_foreign_key, [:dogs, column: "owner_id"]], enable
+      end
+
+      def test_invert_add_foreign_key_with_column_and_name
+        enable = @recorder.inverse_of :add_foreign_key, [:dogs, :people, column: "owner_id", name: "fk"]
+        assert_equal [:remove_foreign_key, [:dogs, name: "fk"]], enable
+      end
+
+      def test_remove_foreign_key_is_irreversible
+        assert_raises ActiveRecord::IrreversibleMigration do
+          @recorder.inverse_of :remove_foreign_key, [:dogs, column: "owner_id"]
+        end
+
+        assert_raises ActiveRecord::IrreversibleMigration do
+          @recorder.inverse_of :remove_foreign_key, [:dogs, name: "fk"]
+        end
+      end
     end
   end
 end
diff --git a/activerecord/test/cases/migration/foreign_key_test.rb b/activerecord/test/cases/migration/foreign_key_test.rb
index fbdb921334..5935062efb 100644
--- a/activerecord/test/cases/migration/foreign_key_test.rb
+++ b/activerecord/test/cases/migration/foreign_key_test.rb
@@ -139,6 +139,25 @@ module ActiveRecord
         output = dump_table_schema "astronauts"
         assert_match %r{\s+add_foreign_key "astronauts",.+dependent: :nullify$}, output
       end
+
+      class CreateCitiesAndHousesMigration < ActiveRecord::Migration
+        def change
+          create_table("cities") { |t| }
+
+          create_table("houses") do |t|
+            t.column :city_id, :integer
+          end
+          add_foreign_key :houses, :cities, column: "city_id"
+        end
+      end
+
+      def test_add_foreign_key_is_reversible
+        migration = CreateCitiesAndHousesMigration.new
+        silence_stream($stdout) { migration.migrate(:up) }
+        assert_equal ["houses_city_id_fk"], @connection.foreign_keys("houses").map(&:name)
+      ensure
+        silence_stream($stdout) { migration.migrate(:down) }
+      end
     end
   end
 end