self.id in model

rubyonrails-talk
1

Happy holidays all!

I have a has_many line in my Members.rb model:

has_many :friends, :class_name => "Member", :finder_sql => "SELECT members.* FROM members, friends WHERE friends.member_id = #{self.id}"

when I run this line: @member.friends, the following query is ran:

select members.* from members, friends where friends.member_id = 53930410

Ignore the logic, the point is, self.id keeps translating to some crazy number like 53930410 instead of what it should be, 2.

Any ideas why?

2

What is happening is that you are getting the object’s object_id instead of it’s saved id. To see what I am talking about, load up irb and make an object, say: a = “A String” then type: a.id It will say this is deprecated, and that you should use object_id instead, but it will also show you the object_id. These numbers vary greatly, but the one returned to you seems to fit right in with this.

However, I am not sure why this is happening in your specific case. Hopefully this will at least help you look into the problem further.

Good luck and happy holidays, Tyler Prete

3

hi,

self is Members not an instance of Members thus with self.id it translates to object_id aka self.id => Members.id

might help

regards gaurav

4

hi,

irb(main):034:0> class A irb(main):035:1> p self irb(main):036:1> def g irb(main):037:2>
p self irb(main):038:2> end irb(main):039:1> end A => nil irb(main):043:0> a=A.new => #<A:0x2c59570> irb(main):044:0> a.g #<A:0x2c59570> => nil

this might give clear picture whats happening

regards gaurav

5

Makes sense.... so that begs the question, how can I access the objects id field as opposed to the object_id?

6

undefined method `' for Member:Class

7

I have a has_many line in my Members.rb model:

has_many :friends, :class_name => "Member", :finder_sql => "SELECT members.* FROM members, friends WHERE friends.member_id = #{self.id}"

when I run this line: @member.friends, the following query is ran:

select members.* from members, friends where friends.member_id = 53930410

Ignore the logic, the point is, self.id keeps translating to some crazy number like 53930410 instead of what it should be, 2.

Any ideas why?

According to documentation simple #{id} should work, but it does not. I think it is a bug. Can anyone confirm this?

Regards, Rimantas

8

Try self[:id] or self.send(:id).

You're probably getting Ruby's object id for the object denoted by self.

--steve

9

self[:id] raises the error listed above... self.send(:id) draws the same object_id as before, not the objects id field from the database

10

hi,

   I doubt you can do it that way.   As id you want is an instance variable and the way you want it is without instantiation.

p=Place.new

=> #<Place:0x3406dc8 @attributes={"place"=>""}, @new_record=true>

p.id

=> nil

Place.id

(irb):8: warning: Object#id will be deprecated; use Object#object_id => 28166940

you can even try p.methods.sort and see the result where you find id and id= methods similar to attr_accessors.......

regards gaurav

11

Now that I look at your code, I think it's a context issue. Consider this, when you call a class method, what is the definition of self? Out of curiosity, why do you need to be so specific in your finder_sql? Wouldn't it be better to do something along the lines of

has_many :friends, :class_name => 'Member', :foreign_key => 'member_id'

Then when you find a member, there is an association to that member's friends. You can simply select within them or use scope.

Am I on the right track?

12

app/models/member.rb class Member < ActiveRecord::Base   has_many :my_friends, :class_name => "Friend", :foreign_key => "member_id"   has_many :friends, :through => :my_friends, :source => :member end

app/models/friend.rb class Friend < ActiveRecord::Base   belongs_to :member end

db/migrate/001_create_members.rb class CreateMembers < ActiveRecord::Migration   def self.up     create_table :members do |t|       # t.column :name, :string       t.column :username, :string     end   end

  def self.down     drop_table :members   end end

db/migrate/002_create_friends.rb class CreateFriends < ActiveRecord::Migration   def self.up     create_table :friends do |t|       # t.column :name, :string       t.column :member_id, :int     end   end

  def self.down     drop_table :friends   end end

ruby script/console

Member.new(:username => "edbond").save

=> true

Member.find(:first).friends

=>

will generate (from log/development.log):   Member Load (0.000361) SELECT members.* FROM members INNER JOIN friends ON members.id = friends.member_id WHERE (friends.member_id = 1)

In through associations on edge rails you can use << method to add new friends. In rails 1.1.6 you can't. You need to create model for join table see: http://blog.hasmanythrough.com/articles/2006/08/19/magic-join-model-creation

"""s.ross писал(а): """

13

Yes you are on the right track... although I removed the difficult logic to simplify the explanation of my problem.

Although at this point, I think I understand the context issue and why it's not working, so I think I'll switch my strategy around and eliminate the use of finder_sql.

Thanks all, Chad

14

Sure, you are getting the wrong self. Try:

has_many :friends, :class_name => "Member", :finder_sql => 'SELECT members.* FROM members, friends WHERE friends.member_id = #{self.id}'

Note the change from "-quotes to '-quotes. You want the #{self.id} to be evalulated later when the SQL is needed, not while you're defining the :finder_sql. (That is, when self is an instance of Member not the class itself.)

You could also have escaped the interpolation "SELECT ... \#{self.id}"

Do you really need :finder_sql in this case? If a member can really have more than one friend, wouldn't you need another table to hold the relationship (i.e., the friendships table)?

class Member < ActiveRecord::Base    has_many :friendships, :dependent => :destroy    has_many :friends, :through => :friendships end class Friendship < ActiveRecord::Base    belongs_to :member    belongs_to :friend, :class => 'Member', :foreign_key => :friend_id end

-Rob

Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com

15

Sure, you are getting the wrong self. Try:

has_many :friends, :class_name => "Member", :finder_sql => 'SELECT members.* FROM members, friends WHERE friends.member_id = #{self.id}'

Note the change from "-quotes to '-quotes. You want the #{self.id} to be evalulated later when the SQL is needed, not while you're defining the :finder_sql. (That is, when self is an instance of Member not the class itself.)

Thank you for pointing this out! I think this is quite a gotcha and deserves a word or two in documentation...

Regards, Rimantas