Cannot use grails g.link in domain class - grails

Question

I have static method in a domain class that returns a url. I need to build that url dynamically but g.link isn't working.
static Map options() {
// ...
def url = g.link( controller: "Foo", action: "bar" )
// ...
}
I get the following errors:
Apparent variable 'g' was found in a static scope but doesn't refer to a local variable, static field or class. Possible causes:
You attempted to reference a variable in the binding or an instance variable from a static context.
You misspelled a classname or statically imported field. Please check the spelling.
You attempted to use a method 'g' but left out brackets in a place not allowed by the grammar.
# line 17, column 19.
def url = g.link( controller: "Foo", action: "bar" )
^
1 error
Obviously my problem is that I am trying to access g from static context, so how do I get around this?

Answer 1

The g object is a taglib, which is not available inside a domain class like it would be in a controller. You can get at it through the grailsApplication as shown here: How To Call A Taglib As A Function In A Domain Class
A better way to do this in Grails 2+ is through the grailsLinkGenerator service, like so:
def grailsLinkGenerator
def someMethod() {
def url = grailsLinkGenerator.link(controller: 'foo', action: 'bar')
}
In both cases, you'll need to do some extra work to get grailsApplication/grailsLinkGenerator from a static context. The best way is probably to grab it off the domainClass property of your domain class:
def grailsApplication = new MyDomain().domainClass.grailsApplication
def grailsLinkGenerator = new MyDomain().domainClass.grailsApplication.mainContext.grailsLinkGenerator

Answer 2

If you're using Grails 2.x you can use the LinkGenerator API. Here's an example, I am re-using a domain class I was testing with earlier so ignore the non-url related functionality.
class Parent {
String pName
static hasMany = [children:Child]
static constraints = {
}
static transients = ['grailsLinkGenerator']
static Map options() {
def linkGen = ContextUtil.getLinkGenerator();
return ['url':linkGen.link(controller: 'test', action: 'index')]
}
}
Utility Class with Static Method
#Singleton
class ContextUtil implements ApplicationContextAware {
private ApplicationContext context
void setApplicationContext(ApplicationContext context) {
this.context = context
}
static LinkGenerator getLinkGenerator() {
getInstance().context.getBean("grailsLinkGenerator")
}
}
Bean Def for New Utility Bean
beans = {
contextUtil(ContextUtil) { bean ->
bean.factoryMethod = 'getInstance'
}
}
If you need the base URL, add absolute:true to the link call.