fk: make `add_foreign_key` reversible.

1 files changed, 16 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)