Question

I have a class method on my Consumer model that functions as a scope (acts on an ActiveRecord::Relation, returns an ActiveRecord::Relation, can be daisy-chained) and returns doubles of some consumers. I want it to only return unique consumers, and I can’t seem to find either a way to do it with Rails helpers or the right SQL to pass in to get what I want. I feel like there’s a simple solution here – it’s not a complicated problem.

I essentially want Array#uniq, but for ActiveRecord::Relation. I tried a select DISTINCT statement

Consumer.joins(...).where(...).select('DISTINCT consumers.id')

It returned the correct ‘uniqueness on consumers.id’ property, but it only returned the consumer ids, so that when I eventually loaded the relation, the Consumers didn’t have their other attributes.
Without select DISTINCT:

my_consumer = Consumer.joins(...).where(...).first
my_consumer.status  # => "active"

With select DISTINCT:

my_consumer = Consumer.joins(...).where(...).select('DISTINCT consumers.id').first
my_consumer.status  # => ActiveModel::MissingAttributeError: missing attribute: status

I didn’t think that an ActiveRecord::Relation would ever load less than the whole model, but I guess it will with the select statement. When I query the Relation after the select statement for the class it contains, it returns Consumer, which seems strange.

Answer 1

.select('DISTINCT consumers.*')