Grails loading data once - grails

Question

I have these 2 domains
class Country {
String name
static hasMany = [cities:City]
}
class City {
String name;
static belongsTo = [country: Country]
}
The data contained in these 2 tables is relatively big, and they're used in all the screens,
every time i choose a country i have to reload all its cities.
How can I load the data only once in memory so i can access it faster in all the screens.
I tried putting cities for eager fetching, and tried using cache plugin.
Thank you

Answer 1

You can configure both domain classes to be cached automatically and also cache the cities relation in Country:
class Country {
String name
static hasMany = [cities:City]
static mapping = {
cache true
cities cache:true
}
}
class City {
String name
static belongsTo = [country: Country]
static mapping = {
cache true
}
}

Answer 2

Caching is often a good strategy, but remember that caches have expiry parameters so if left idle your app may reload from the DB again. Depending on your cache provider you'll have to tune this, eg For ehcache edit your ehcache.xml in the grails config folder and set (cache name is the same as your Domain class including package name):
<cache name="Country" maxElementsInMemory="1000" timeToIdleSeconds="0" timeToLiveSeconds="0"/>
You should also move the query into a service, the service is by default singleton scoped and the service method also cachable.
An alternative is to store them in application scope such as in your Bootstrap.groovy run the query and assign the results:
servletContext.countries = Country.list()
Retrieve them in the same way, eg
in a controller:
List<Country> countries = servletContext.countries
or gsp:
<g:each var="country" in="${application.countries}">
${country}
</g:each>
If you have eager fetching on then you should see no DB hits.