Ruby-on-Rails: Selecting distinct values from the model

Question

The docs: http://guides.rubyonrails.org/active_record_querying.html#selecting-specific-fields

Clearly state that:

query = Client.select(:name).distinct
# => Returns unique names

However, when I try that in my controller, I get the following error:

undefined method `distinct' for #<ActiveRecord::Relation:0xb2f6f2cc>

To be clear, I want the distinct names, like ['George', 'Brandon'], not the clients actual records. Is there something that I am missing?

Answer 1

The .distinct option was added for rails 4 which is what the latest guides refer to.

Rails 2

If you are still on rails 2 you will need to use:

Client.select('distinct(name)')

Rails 3

If you are on Rails 3 you will need to use:

Client.select(:name).uniq

If you look at the equivalent section of the rails 3 guide you can see the difference between the two versions.

Answer 2

There are some approaches:

1. Rails way:

   Model.select(:name).distinct
   

2. Semi-rails way

   Model.select("DISTINCT ON(models.name) models.*")
   

   The second allows you to select the first record uniqued by name, but in the whole matter, not only names.

Answer 3

If you do not want ActiveRecord::Relations returned, just an array of the names as strings, then use:

Client.distinct.pluck(:name)

To get an ordered result set:

Client.order(:name).distinct.pluck(:name)