Rails 4 query unique by single attribute

Question

So this is more of an arel question than anything but here\'s what I am trying to do.

I have three objects lets say, called Items

Answer 1

I can't comment on posts yet, so, putting this as another answer for the question.

In case of someone still searches for this, @BananaNeil's answer is correct. However, putting distinct in select didn't work for me (Rails 5.2.2). Separating these two did fix my problem.

klass.where(
  # Your query or whatever
).distinct.select('on (attribute) *')