ERROR: delete on table violates foreign key constraint. Key id is still referenced from table (many)

From Rails v4.2 you can do this:

Create a migration to update the foreign keys

20160321165946_update_foreign_key.rb

class UpdateForeignKey < ActiveRecord::Migration
  def change
    # remove the old foreign_key
    remove_foreign_key :posts, :users

    # add the new foreign_key
    add_foreign_key :posts, :users, on_delete: :cascade
  end
end

Are you using delete or destroy to remove the objects? I think you are using delete and you want to use destroy

See http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#module-ActiveRecord::Associations::ClassMethods-label-Delete+or+destroy-3F

My issue was that i am using @auction.delete (visible in the screenshot I posted) when trying to remove a record.

Delete will ignore any callbacks I have in place. So even though I have a dependent destroy clause, it is not being called - hence Rails is throwing an error. If/When I changed the code to read @auction.destroy, the call-back got invoked and it solved the problem.

Reference: Difference between Destroy and Delete