Rails: Order with nulls last

Question

In my Rails app I\'ve run into an issue a couple times that I\'d like to know how other people solve:

I have certain records where a value is optional, so some recor

Answer 1

For posterity's sake, I wanted to highlight an ActiveRecord error relating to NULLS FIRST.

If you try to call:

Model.scope_with_nulls_first.last

Rails will attempt to call reverse_order.first, and reverse_order is not compatible with NULLS LAST, as it tries to generate the invalid SQL:

PG::SyntaxError: ERROR:  syntax error at or near "DESC"
LINE 1: ...dents"  ORDER BY table_column DESC NULLS LAST DESC LIMIT...

This was referenced a few years ago in some still-open Rails issues (one, two, three). I was able to work around it by doing the following:

  scope :nulls_first, -> { order("table_column IS NOT NULL") }
  scope :meaningfully_ordered, -> { nulls_first.order("table_column ASC") }

It appears that by chaining the two orders together, valid SQL gets generated:

Model Load (12.0ms)  SELECT  "models".* FROM "models"  ORDER BY table_column IS NULL DESC, table_column ASC LIMIT 1

The only downside is that this chaining has to be done for each scope.