Question

I’m trying to set the order for Topic index by most recent Comment. This is working:

Topic.joins(:comments).order("comments.created_at desc")

But it lists the Topics more than one time.

Is there a way to limit the times each topic is displayed to one?

Answer 1

The most elegant way I found to solve the problem is to add touch to the polymorphic association in the comment model:

belongs_to :commentable, :polymorphic => true, touch: true

If you’re not using a polymorphic association, you can use:

belongs_to :topic, touch: true

Then, all I had to do was change the default scope in the topic model to updated_at

default_scope order: 'topics.updated_at DESC'

Adding touch to comment means that every time a comment is added to topic, it updates the updated_at column in topics.

In the controller I am using:

@topics = Topic.order(sort_column + " " + sort_direction).paginate(:per_page => 20, :page => params[:page])

Topic.all or something else could work there as well.

Thanks to my super friend Alain for pointing this out to me.