Cannot use grails g.link in domain class

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.