ActiveRecord.id does not work within named_scope block

rubyonrails-talk
1

Hi,

Trying to create a named_scope that would check that the record is not itself.

I have companies and contacts, where a contact can be a primary contact for a company:

class Company   has_many :contacts end

class Contact < ActiveRecord::Base   belongs_to :company

  named_scope :primary, :conditions => { :is_primary => true } do     def mark_as_non_primary!       each { |p| p.update_attribute(:is_primary, false) }     end   end

  named_scope :but_not_itself, :conditions => ['contacts.id != ?', id] end

So I would like to do something like this from Contact model:

  company.contacts.primary.but_not_itself.mark_as_non_primary!

However this does not work because id method within but_not_itself named_scope returns an Object.id (instance id) and not ActiveRecord id (database id).

How do I make it work?

Thanks!

2

Hi,

Trying to create a named_scope that would check that the record is not itself.

I have companies and contacts, where a contact can be a primary contact for a company:

class Company has_many :contacts end

class Contact < ActiveRecord::Base belongs_to :company

named_scope :primary, :conditions => { :is_primary => true } do def mark_as_non_primary! each { |p| p.update_attribute(:is_primary, false) } end end

named_scope :but_not_itself, :conditions => ['contacts.id != ?', id] end

So I would like to do something like this from Contact model:

    company\.contacts\.primary\.but\_not\_itself\.mark\_as\_non\_primary\!

However this does not work because id method within but_not_itself named_scope returns an Object.id (instance id) and not ActiveRecord id (database id).

The reason this does not work is because that expression "id" is evaluated when named_scope is call to create the scope, ie when the class is loaded, so self is the class Contact. It's the same reason why doing :conditions => ['created_at < ?', 1.day.ago] won't work properly: the 1.day.ago is evaluated once, at class load time and then never again.

Luckily instead of passing a hash of options you can pass a lambda that returns a hash of options. Since that proc will be called when the scope is loaded and in the right context you should be fine.

Fred

3

Hi Fred,

Thanks for your input.

So far I changed that named_scope into this: named_scope :but_not_itself,   lambda { |id| { :conditions => ['contacts.id != ?', id]} }

Is that what you meant?

Is there a better way to do this?

Now I have to do this: company.contacts.primary.but_not_itself(self.id).mark_as_non_primary!

seems, to me at least, kind of ugly having to pass self.id... :slight_smile:

By the way my inspiration for this came from http://ryandaigle.com/articles/2008/3/24/what-s-new-in-edge-rails-has-finder-functionality Where the author has User.inactive.activate to very neatly activate inactive users.