Grails db-reverse-engineer id and version - grails

Question

I am still new to Grails and Hibernate so if you answer keep in mind I have only used the IDE for 5 days. I have a MYSQL db I am trying to connect to. I set the DB to update as I will need to later on. Then I run the db-reverse-engineer plugin and it auto generates the groovy files in STS for all the tables. When I look at the files I notice in the file a static mapping. I tested one table and created its controller to show all records. It ran perfect. When I looked at the table structure it create 2 new columns "id" and "version". So I noticed the static mapping looks like this:
class TopTen {
Integer ttMlId
Integer ttWeekId
Integer ttAmount
Integer ttRank
static mapping = {
id column: "tt_id"
version false
}
}
When I remove these then it doesn't work at all. I can understand the second line but not why it would create a new column in the DB, and I don't understand what version is or why it puts it there when reverse engineering.
Here is the db table in MySQL database version 5.0.51
DROP TABLE IF EXISTS `top_ten`;
CREATE TABLE `top_ten` (
`tt_id` int(10) unsigned NOT NULL auto_increment,
`tt_ml_id` int(10) unsigned NOT NULL default '0',
`tt_week_id` int(10) unsigned NOT NULL default '601',
`tt_amount` int(10) unsigned NOT NULL default '0',
`tt_rank` int(10) unsigned NOT NULL default '0',
PRIMARY KEY (`tt_id`)
) ENGINE=InnoDB AUTO_INCREMENT=511 DEFAULT CHARSET=latin1;

Answer 1

Hibernate can use optimistic locking and by default it's enabled for all GORM domain classes. But if you don't have a column to use for that in a legacy table or if you want to explicitly disable it for some reason, you can add version false to the mapping block and it won't be active.
Optimistic locking is implemented by comparing the version you think you're editing with the current version at the time the row is updated, and if there's a mismatch it's assumed that there was another user's edit between when you read the row to display the edit form and when you submitted the updated data. It's called optimistic since there's no explicit locking, which is safer but expensive, and it's hoped that two users won't edit the same row at the same time.
If you're seeing a new 'id' column in the database with that mapping block, something is wrong. That should tell GORM that the primary key column has a non-standard column name of 'ttx_id' and use that instead of the 'id' column that it typically uses. Please create a bug report at http://jira.codehaus.org/browse/GRAILSPLUGINS under the Grails-Reverse-Engineer component and include the current database table SQL and the contents of the generated domain class and I'll take a look.