Question

I have a model with a has_many relationship, and a scope to determine whether or not it has any children, such as:

  scope :with_nomination, :include => [:nomination], :conditions => "nominations.service_id IS NOT NULL"

Using this, I can do something like Service.with_nomination and receive a list of all services with nomination children.

The problem is that when I do something like Service.select("id, firstName, lastName").with_nomination ActiveRecord in essense does a SELECT * FROM services which is very bad and does not utilize the indexes I so painstakingly set up.

How can I either rephrase my query or modify my scopes to work with the .select() command?

Answer 1

Turns out in the syntax I was using, a select is not possible, so it does a select * and any further selects are already overriden.

I re-wrote the scopes like so:

scope :no_nomination, joins("LEFT JOIN nominations ON nominations.service_id = services.id").where("nominations.service_id IS NULL")
# important distinction here, the left join allows you to find those records without children

scope :with_nomination, joins(:nomination).where("nominations.service_id IS NOT NULL")

Using this syntax allows me to do something like Service.select(:id,:user,:otherfield).with_nomination