rails don't find the attribute

Question

I have this model

#post.rb
class Post < ActiveRecord::Base
    belongs_to :user
    after_initialize :create_token
    attr_accessible :token
    protected
    def create_token
      self.token = "#{Digest::MD5.hexdigest("#{self.id}")[0,4]}"
    end 
end

in rails c

Post.find(:all,:conditions => { :user_id => 11})
 => [#<Post id: 26, content: "<p><strong>Yao Ming</strong> (<a shape=\"rect\" title...", user_id: 11, created_at: "2011-07-12 15:08:30", updated_at: "2011-07-12 15:08:30", title: "Yao Ming", guid: "0010f6c3-040b-4e13-aa38-3a002e6f2022", contentHash: "\xB9\\\xCBK\xB0A>4\xC4~\xFC\"\xEA7\xA6y", token: "4e73">]

when the token: "4e73" , but when I try

Post.find(:all,:conditions => { :user_id => 11, :token => "4e73"}) 
 => []

I get [] , why?

more information

Post.find(:all,:conditions => { :user_id => 11}).first.token.class
=> String 

Post.find(:all,:conditions => { :user_id => 11}).first.token
=> "3769" 

Answer 1

According to Rails Guides:

The after_initialize callback will be called whenever an Active Record object is instantiated, either by directly using new or when a record is loaded from the database.

You should probably find another way to initialize this 'token' field, otherwise it will be changed every time you reload the record from database.

Answer 2

As Eugen says, That is the problem, In all case Rails has no native way to does that, so what you have to do is:

class Post < ActiveRecord::Base
    belongs_to :user
    after_initialize :create_token
    attr_accessible :token
    protected
    def create_token
        if new?
          self.token = "#{Digest::MD5.hexdigest("#{self.id}")[0,4]}"
        end
    end 
end

or simply

class Post < ActiveRecord::Base
    belongs_to :user
    attr_accessible :token
    protected
    def after_initialize
        if new?
          self.token = "#{Digest::MD5.hexdigest("#{self.id}")[0,4]}"
        end
    end 
end

Answer 3

Well, to build an attribute based on the id , the id must exist. Finally, do this:

after_create :create_token

def create_token
  self.token = "#{Digest::MD5.hexdigest("#{self.id}")[0,4]}"
  self.save
end

Answer 4

I would use

before_create :create_token

so it's only generated when the record is first inserted into the database.