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Id Generation

Database ID Generator

The plugin comes with an implementation of hibernate identity generator for a cross database and NoSQL way to assign Long ids from an in memory incrementor. It uses a central table to track the last used id for each table. This helps a lot when dealing with associations and relationships. It also increases the performance of batch inserts.

NewObjectId table

The table name is configurable and will get created if it does not exist. You can also create the table as shown below and add indexes if desired.

create table NewObjectId
(
    KeyName varchar(255) not null primary key,
    NextId bigint not null
)
;

Here key name will be the name of the tables and NextId is the next id to return for the given table.

Configure Identity generator globally.

The identity generator can be configured globally in application.groovy as shown below.

grails {

    gorm.default.mapping = {
        id column: 'id', generator:'gorm.tools.hibernate.SpringBeanIdGenerator'
    }
}

This will use the SpringBeanIdGenerator for all domains in the application. However it can be done per domain too if required.

Using IdGenerator programmatically

Plugin defines a bean with name idGenerator that can be used to programmatically generate new Ids. Here is an example domain class.

class Book {
    transient idGenerator

    def beforeInsert() {
        if(!id) id = idGenerator.getNextId('Book.id') // or idGenerator.getNextId(this)
    }
}

Identity generator will check in NewObjectId table for keyName Book If it exists, it will return the value of NextId or else it will insert a new row in NewObjectId table.

How it works

By default the following beans are enabled.

jdbcIdGenerator
A Jdbc implementation of the IdGenerator, it uses NewObjectId central table to query the new ids.

idGenerator(BatchIdGenerator)
Idgenerator implementation that caches a range of values in memory by the key name. It caches a batch of id for each key and increments in memory thus provides better performance. Internally it uses jdbcIdGenerator to query for next batch of ids.

BatchIdGenerator by default uses allocationSize size of 100. Which can be changed by overriding the spring bean as shown below.

 idGenerator(BatchIdGenerator){
    generator = ref("jdbcIdGenerator")
    allocationSize = 50
  }

The plugin by default configures the BatchIdGenerator as default idgenerator. If you need to use another idgenerator or provide a custom implementation, you can override the idGenerator spring bean.

jdbcTemplate This plugin also configures JdbcTemplate which can be used for low level jdbc access. It uses TransactionAwareDataSourceProxy so the queries run through the jdbcTemplate will be part of the current transaction.