Can you have a scope which checks from absence?

Question

I have an Invites table in my database and when i'm perform a task as a user I want to pass an Event.id to a scope User.not_invited_to(event)

How do I build this scope to check if the user ID is NOT in there?

class User
  has_many :invites, :foreign_key => 'participant_id'
  ...
end

class Invite
  belongs_to :participant, :class_name => "User", :foreign_key => "participant_id"
  ...
end

I can do it this way. `scope :not_invited, lambda{|event| where("id not in (?)", event.invites.collect{|i| i.participant_id }.join(',')) }` — Joseph Le Brech, Apr 04 '13 at 09:30
can you give more information about your schema ? there may be a more efficient way to do this — m_x, Apr 04 '13 at 12:50

score 0 · Accepted Answer · answered Apr 04 '13 at 13:45

0

You can use event.invite_ids:

scope :not_invited, lambda { |event| where("id not in (?)", event.invite_ids) }

answered Apr 04 '13 at 13:45

Mischa

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I did not realise this, i've being using collect a lot. so would .._ids do that for me? – Joseph Le Brech Apr 04 '13 at 13:47
Yes, `*_ids` does that for you. It's [one of the things added](http://edgeguides.rubyonrails.org/association_basics.html#has-many-association-reference) to your ActiveRecord object when it has a `has_many` association to an other model. – Mischa Apr 04 '13 at 13:58

Can you have a scope which checks from absence?

1 Answers1