(Quick Reference)
embedded
目的
Purpose
Supports embedding domain components into domain classes - otherwise known as
composition.
使用例
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:
| Column | Type |
|---|
| NAME | VARCHAR(255) |
| BORN_IN_COUNTRY_ISO3 | VARCHAR(255) |
| BORN_IN_COUNTRY_NAME | VARCHAR(255) |
| LIVES_IN_COUNTRY_ISO3 | VARCHAR(255) |
| LIVES_IN_COUNTRY_NAME | VARCHAR(255) |
詳細
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/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/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.
