(Quick Reference)

embedded

Purpose

Supports embedding domain components into domain classes - otherwise known as composition.

Examples

Given these domain classes:

class Person {

String name Country bornInCountry Country livesInCountry

static embedded = ['bornInCountry', 'livesInCountry'] }

// If you don't want an associated table created for this class, either // define it in the same file as Person or put Country.groovy under the // src/groovy directory. class Country { String iso3 String name }

Grails will generate a person database table that looks like:

ColumnType
NAMEVARCHAR(255)
BORN_IN_COUNTRY_ISO3VARCHAR(255)
BORN_IN_COUNTRY_NAMEVARCHAR(255)
LIVES_IN_COUNTRY_ISO3VARCHAR(255)
LIVES_IN_COUNTRY_NAMEVARCHAR(255)

Description

An embedded component does not store its data in its own table as a regular domain class relationship does. Instead, the data is included in the owner's table. So in the above example, the Country fields appear in the person table. This means that queries are faster because there is no join required, but you may end up with duplicate data across tables.

The embedded component class is typically declared in the same source file as the owning class or in its own file under src/main/groovy. You can put the component class under grails-app/domain, but if you do so Grails will automatically create a dedicated table for it. Putting the class under src/main/groovy is usually the best option because you can then share the component across multiple domain classes.

Querying on embedded properties is no different from querying on regular relationships, so you can for example still do:

Person.findAllByBornInCountry(brazil)
Person.findAllByLivesInCountry(france)

where brazil and france are instances of Country.