class ActiveRecord::ConnectionAdapters::PostgreSQL::SchemaCreation

def visit_AddForeignKey(o)
  super.dup.tap do |sql|
    if o.deferrable
      sql << " DEFERRABLE"
      sql << " INITIALLY #{o.deferrable.to_s.upcase}" unless o.deferrable == true
    end
    sql << " NOT VALID" unless o.validate?
  end
end