From: Brian Candler <b.candler@...>
Date: 2010-09-05T00:51:02+09:00
Subject: Re: ActiveRecord and incrementing the key

Abder-Rahman Ali wrote:
> How does the database server manage the incrementing of the key? What is
> meant here by the database server is what manages the incrementing of
> the key?

Mysql: primary key is declared as an AUTO_INCREMENT column.
http://dev.mysql.com/doc/refman/5.1/en/example-auto-increment.html

Sqlite: if there is an INTEGER PRIMARY KEY then it's the 
automatically-assigned ROWID.
http://www.sqlite.org/autoinc.html

Oracle: uses a sequence, something like
INSERT INTO foo(id,bar) VALUES(foo_seq.nextval,?)

And so on - each of the database adapters has their own logic.

See for example 
activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

      NATIVE_DATABASE_TYPES = {
        :primary_key => "int(11) DEFAULT NULL auto_increment PRIMARY 
KEY".freeze,

-- 
Posted via http://www.ruby-forum.com/.