8

I have a situation where the behavior of an existing app is changing and it's causing me a major headache.

My app has Photos. Photos have a status: "batch", "queue", or "complete". All the existing Photos in the app are "complete".

99% of the time I need to only show complete photos, and in all of the existing codebase I need every call to Photos to be limited to only complete photos.

However, in the screens related to uploading and classifying photos I need to be able to fairly easily override that default scope to show batched or queued photos.

Like many others, I need to find a way to easily override the default scope in certain situations. I looked at these questions (1, 2) and they don't seem to answer what I'm looking for.

The code I wish worked is this:

class Photo < ActiveRecord::Base
  ...
  default_scope where(:status=>'complete')
  scope :batch, unscoped.where(:status=>'batch')
  scope :queue, unscoped.where(:status=>'queue')
  ...
end

However, that doesn't work. I tried wrapping the scope methods in lambdas, and that didn't work either.

I realize default_scope comes with baggage, but if I can't use it with overrides then I'm looking at adding scope :complete ... and having to comb through every call to photos in my existing app and add .complete in order to filter unprocessed photos.

How would you solve this problem?

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Andrew
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2 Answers2

6

def self.batch
  Photo.unscoped.where(:status=>"batch")
end
This thread is more authoritative: Overriding a Rails default_scope
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klochner
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  • I thought of this, and I tried it, but then I end up with this problem: `user.photos.batch` returns all photos (because the unscoped call on the model breaks the association). – Andrew Aug 02 '11 at 22:22
  • you're semi-screwed here. You could add a User::photos method that returns the unscoped photos for the user, but otherwise default_scope is kind of nasty. – klochner Aug 02 '11 at 22:38
  • Out of curiosity, do you know what it would take to override the default_scope method to change the behavior? I'm interested in taking a stab at that, but not sure where to begin. – Andrew Aug 02 '11 at 23:38
  • here's the rdoc, click 'show source' to see how default_scope works: http://api.rubyonrails.org/classes/ActiveRecord/Base.html#method-c-default_scope – klochner Aug 02 '11 at 23:46
  • Great, thanks! I'll leave this question open a bit longer in case anyone else has any thoughts, but if no one does I'll accept your answer as it does kind of work. – Andrew Aug 03 '11 at 00:01
  • also - here's the source for ActiveRecord::Base - https://github.com/rails/rails/blob/master/activerecord/lib/active_record/base.rb – klochner Aug 03 '11 at 00:04
4

I give it a shot. Lets say you want to remove a where clause from a default scope (and not just override it with another value) and keep associations you can try this:

class Photo < ActiveRecord::Base
  default_scope where(:status => 'complete').where(:deleted_at => '').order('id desc')

  def self.without_default_status
    # Get the ActiveRecord::Relation with the default_scope applied.
    photos = scoped.with_default_scope
    # Find the where clause that matches the where clause we want to remove 
    # from the default scope and delete it.
    photos.where_values.delete_if { |query| query.to_sql == "\"photos\".\"status\" = 'complete'" }
    photos
  end

end
schneikai
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