I need a way to set a counter that will show how many of the model have been created and put this in each instance. This will allow me to use the record number as an input to another field before id is set. After things are settled, the real id number can be substituted for the counter.
I've tried new in the controller, but that's for a create action from the app.
Thanks Bob
If you do that and two users come along at the same time and make new objects then they will both get the same number. Can you not just use a before_save filter to set the field? If you think not can you explain what you are trying to do (and why) in more detail as there is almost certainly a better solution.
Colin
You can use also after_initialize checking if the counter is already setted
after_initialize :set_counter
def set_counter
self.counter ||= ModelName.all.count
end
Please don't *ever* do this. If you want a count of all the objects in a table, use "ModeName.count". Using ".all.count" will instantiate an array of all of the objects just to do a count of the array... this could be very slow with a big table.
Ops, sorry…I don’t know why I add .all 
I think actually he asked about something counter-caching solution for stand-alone model/table. Good question, for the best approach it has to be realized on a database level. The second approach is to build additional caching table to keep counter values for anything you want. The last one is not so elegant.
Imagine 'create' action.
During the period from the instance is initialized: @user = User.new(params[:user]) to the moment it saved @user.save
anyone else can create user object(s), so your @user will be saved with incorrect counter value.
Maybe the OP really wants a “sequence” (a guaranteed unique number that is more or less monotomically going up).
The OP may be used to the concept that the primary ID of a record upon
creation is such a sequence. But maybe he needs that number before the record is saved. (e.g. to set a serial number that is saved in the record).
If that is the business requirement, 3 solutions:
in Postgresql and probably in all databases) and use that to calculate the unique and more or less monoticly increasing serial number. Do NOT couple that “business id” with the actual internal database id.
If you want to use the database id, then you could use an external sequence generator and set the Object.id manually before saving (than configure your db in a way that the primary key is set from the application).
do an after_create (create the object with most data filled in, the create will generate the database id and in the after_create calculate the other field (e.g. serial number) and save again … this is then an
“update” so the “after_create” will not be triggered again). You may need some more tricks to make sure this “serial number” field cannot be modified, otherwise it could be out of sync with you internal database
id (that is “back to (1) above” don’t link the “serial number” with the database id, just make it a separate column with a unique index and use a separate sequencer to generate those unique codes).
HTH,
Peter
It seems a bit of explanation is in order..
after_create, after_initialize, and the database won't help me.. I need this value to be available as soon as new creates a new object in the view, before any saving. I have the logic set to do this with existing records. What I am trying to do is have a unique value set in each new record so that they can be part of a radio button list.
This is how the new objects are created
<%= link_to_function "Add a Person" do |page| page.insert_html :bottom, 'empty', :partial => 'shared/ person', :locals => {:temp => @temp,:household => @household}, :object => Person.new end %>
My app is used at the signup table of a foodbank. My app has a household record that has address, zip, phone, etc. This has a child model called people with.. guess what... people :> There are radio buttons referencing the record id next to each person where the head of household can be selected. This is where the problem lies. No problem with existing people, but new ones have no id yet. I have added a variable to the people model to hold a counter. I have the logic to look back at the record after save, find the id of the wanted record, and replace the counter with the correct value. Now all I need is a way to set the counter at each new record. Hope this makes it clearer.
Thanks Bob
Just ALMOST fixed this thanks to google..
in person.rb def initialize(params = nil) super() self.hoh = $hoh $hoh = $hoh - 1 end
This will set the model to the value in $hoh and decrement it once, but after that the $hoh = $hoh - 1 won't execute. If I make more than 1 record, all values are the same.. Please help!!
Thanks Bob
Indeed.
And maybe better to not mess with the def initialize, but use the
after_initialize function that is provided by Rails. I did it like this.
../lib/uuid_helper.rb
require ‘uuidtools’
module UUIDHelper extend ActiveSupport::Concern
included do after_initialize :set_uuid def set_uuid unless uuid # Note 1 below
self.uuid = UUIDTools::UUID.random_create.to_s
end
end
end end
../app/model/person.rb
class Person < ActiveRecord::Base
include UUIDHelper …
end
Note 1: Be careful, it is a little tricky to only set the value of the uuid when it is not yet present, otherwise reading back the value from the database will build a new instance of Person with a
new random uuid. The code above is well tested and works.
Maybe you will also need to add ../lib to your default load path. In config/application.rb
# Custom directories with classes and modules you want to be autoloadable.
config.autoload_paths += %W(#{config.root}/lib)
config.autoload_paths += Dir["#{config.root}/lib/**/"]
HTH,
Peter
*** Available for a new project ***
Peter Vandenabeele
I don't have a config/application.rb. Forgot to mention it, but I'm using 2.3.9 until I get rid of bugs, then the 3.0 project starts.. :> Can this be done for 2.3.9?
Thanks Bob
Finally found it. Here it is for anyone else in similar trouble.
In the view
<%= link_to_remote "Add a Person", :url => "/people/add_person" %>
In the controller
def add_person person = Person.new() person.hoh = $hoh $hoh = $hoh - 1 render :update do |page| page.insert_html :bottom, 'empty', :partial => 'shared/ person', :object => person end end
This will add a new object AND allow the play with the hoh in the new model AND decrement it for the next new object. As usual, everything is possible in Rails, once you find an allowed way to do it,
Bob <bsm2th@gmail.com>
Global variables? For the love of all that's OO, at least hide it behind a singleton :-/ *shakes head*