# ActiveRecord and incrementing the key **URL:** \ **Category:** Ruby\ **Created:** [September 4, 2010, 5:17pm UTC](https://www.ruby-forum.com/t/activerecord-and-incrementing-the-key/194413 "2010-09-04T17:17:13Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![swengineer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/97f17d/32.png) [@swengineer](https://www.ruby-forum.com/u/swengineer)\ **Post date:** [September 4, 2010, 5:17pm UTC](https://www.ruby-forum.com/t/activerecord-and-incrementing-the-key/194413/1 "2010-09-04T17:17:13Z")
In “The Rails Way” book, the following is mentiond in Chapter (6):Working with ActiveRecord “Also by convention, ActiveRecord will expect an id column to use as primary key. It should be an integer and [[incrementing of the key should be managed automatically by the database server when creating new records]].” 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? Is there an example that may make this point more clear. For example, the following “database server” increments… Thanks. ---
**Author:** ![swengineer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/97f17d/32.png) [@swengineer](https://www.ruby-forum.com/u/swengineer)\ **Post date:** [September 4, 2010, 5:48pm UTC](https://www.ruby-forum.com/t/activerecord-and-incrementing-the-key/194413/2 "2010-09-04T17:48:13Z")
Abder-Rahman A. 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](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](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, ---
**Author:** ![swengineer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/97f17d/32.png) [@swengineer](https://www.ruby-forum.com/u/swengineer)\ **Post date:** [September 4, 2010, 5:51pm UTC](https://www.ruby-forum.com/t/activerecord-and-incrementing-the-key/194413/3 "2010-09-04T17:51:48Z")
Thanks @Brian for the clarification. ---
**Author:** ![swengineer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/97f17d/32.png) [@swengineer](https://www.ruby-forum.com/u/swengineer)\ **Post date:** [September 6, 2010, 4:39pm UTC](https://www.ruby-forum.com/t/activerecord-and-incrementing-the-key/194413/4 "2010-09-06T16:39:27Z")
Hi, On 04.09.2010 17:17, Abder-Rahman A. 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? > > Is there an example that may make this point more clear. For example, > the following “database server” increments… You need to consult your database documentation how to achieve this; it varies from one product to another. E.g. in MySQL it’s using “auto\_increment” on the primary key [1] HTH [1] [http://dev.mysql.com/doc/refman/5.6/en/example-auto-increment.html](http://dev.mysql.com/doc/refman/5.6/en/example-auto-increment.html) ---
**Author:** ![swengineer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/97f17d/32.png) [@swengineer](https://www.ruby-forum.com/u/swengineer)\ **Post date:** [September 6, 2010, 4:39pm UTC](https://www.ruby-forum.com/t/activerecord-and-incrementing-the-key/194413/5 "2010-09-06T16:39:29Z")
On Sat, Sep 4, 2010 at 10:17 AM, Abder-Rahman A. \< removed\_email\_address@domain.invalid\> wrote: > In “The Rails Way” book, the following is mentiond in Chapter > (6):Working with ActiveRecord > > “Also by convention, ActiveRecord will expect an id column to use as > primary key. It should be an integer and [[incrementing of the key > should be managed automatically by the database server when creating new > records]].” > > 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? > > Is there an example that may make this point more clear. For example, > the following “database server” increments… > > ## Thanks. > > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). If you’re using migrations, then it will add this by default, unless you tell it not to (meaning don’t worry, it will be there). I’d probably look at [Active Record Migrations — Ruby on Rails Guides](http://guides.rubyonrails.org/migrations.html) as my first resource in that situation, though you’ll want to check your version of AR against whatever they’re using, they released AR 3 five days ago [activerecord | RubyGems.org | your community gem host](http://rubygems.org/gems/activerecord) those guides were last updated on July 15th. You’re probably fine, but just be aware of that if examples don’t seem to be working. If you’re not using migrations, then you’ll want to do something like this > CREATE TABLE IF NOT EXISTS posts ( id INTEGER PRIMARY KEY ASC AUTOINCREMENT, subject Text, body Text, author Text, message\_board\_id Integer ); The second line defines the id, and will depend on your database, for instance, I got the syntax for that one at [http://www.sqlite.org/lang\_createtable.html](http://www.sqlite.org/lang_createtable.html) ---
**Author:** ![swengineer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/97f17d/32.png) [@swengineer](https://www.ruby-forum.com/u/swengineer)\ **Post date:** [September 6, 2010, 4:58pm UTC](https://www.ruby-forum.com/t/activerecord-and-incrementing-the-key/194413/6 "2010-09-06T16:58:37Z")
Thanks @Josh.