Question

I have a simple time-tracking app, that has projects, tasks, and entries.

The setup is straight-forward:

class Project < ActiveRecord::base
  has_many :tasks
  has_many :entries, :through => :tasks
end

class Task < ActiveRecord::base
  belongs_to :project
  has_many :entries

  default_scope order("name asc") # this causes problems
end

(Entry is entirely straight-forward, so I’ve left it out)

However, I’m running into trouble when trying to do custom ordering of entries selected from a project. Specifically, I’m trying to select the latest entry like so:

latest_entry = project.entries.order("created_at desc").first

But due to the :through => :tasks and the default_scope that Task has, the actual query that Rails executes becomes:

SELECT `entries`.* FROM `entries`
INNER JOIN `tasks` ON `entries`.`task_id` = `tasks`.`id`
WHERE `tasks`.`project_id` = 23
ORDER BY name asc, entries.date desc LIMIT 1 -- wrong order!

Note the ORDER BY clause – it includes the default_scope from Task, and only after that does it include the order I specified.

So basically, I don’t get the latest entry of all entries in the project, but only the latest in the first task.

Is there any way around that? Seems like there should be a way to ignore/negate default_scope on a through-model (without completely dropping the default_scope)

Answer 1

How about reorder:

latest_entry = project.entries.reorder("created_at desc").first