On Feb 8, 7:11 am, Peter Vandenabeele wrote:
On Wed, Feb 8, 2012 at 10:39 AM, Colin Law wrote:
On 8 February 2012 07:12, Bob Smith wrote:
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.
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.
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:

1) don't do it that way. Use a separate sequence generator (which exists
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.

2) 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).

3) 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

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postedFeb 8, '12 at 7:13a
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