Grails getSomething(int i) method doesn't compile

Question

Can someone tell me why this Grails domain class will not compile (at runtime)?

class Person {
    String name

    String getSomething(int i) {
    }
}

I get this error when I run with grails run-app:

2008-12-27 15:26:33.955::WARN:  Failed startup of context org.mortbay.jetty.webapp.WebAppContext@187e184{/asrs2,C:\Steve\asrs2/web-app}
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
        at java.security.AccessController.doPrivileged(Native Method)
        at RunApp_groovy$_run_closure2_closure7.doCall(RunApp_groovy:67)
        at RunApp_groovy$_run_closure2_closure7.doCall(RunApp_groovy)
        at Init_groovy$_run_closure6.doCall(Init_groovy:131)
        at RunApp_groovy$_run_closure2.doCall(RunApp_groovy:66)
        at RunApp_groovy$_run_closure2.doCall(RunApp_groovy)
        at RunApp_groovy$_run_closure1.doCall(RunApp_groovy:57)
        at RunApp_groovy$_run_closure1.doCall(RunApp_groovy)
        at gant.Gant.dispatch(Gant.groovy:271)
        at gant.Gant.this$2$dispatch(Gant.groovy)
        at gant.Gant.invokeMethod(Gant.groovy)
        at gant.Gant.processTargets(Gant.groovy:436)
        at gant.Gant.processArgs(Gant.groovy:372)
Caused by: java.lang.NullPointerException
        at java.lang.Class.isAssignableFrom(Native Method)
        ... 13 more

If I change the method getSomething to doSomething then it works. Is getSomething(int i) somehow being treated as a bean method?

Follow up: This is a Grails bug which will be fixed in 1.2.

Answer 1

Before I answer the question let me tell you my environment:
Grails 1.0.4
Java 1.6.0_10-beta
Groovy 1.6-RC-1
on a Windows Vista machine

In grails, dynamic get methods are added at runtime for all the fields in the domain class. For the Person class metioned in the question, a getName() method would be added at runtime which would allow one to use it wtithout defining it. Now the problem, with getSomething(int i) is that you do not have a field called String something in your class. If you try adding a method called getName(int i) it would work without any issues or if you add a field String something then the getSomething() method would work.

I hope this resolves the issue for the time being...I would keep looking and post an updates on the exact working soon.

Answer 2

Well, you've got two problems:

1. Domain classes in Grails try to make sure that every property has a getter and setter during startup. It does this by looking for all the getters, and making sure an appropriate setter exists. So, if you have a getSomething(), you have to have a setSomething( def something ), even if there is no property "something" in the class. Really, by creating the getSomething() function, you've implied that there is such a property, and you must create a setSomething() as well.

2. Getters do not take arguments. Yours does. Now I realize you weren't thinking this was a "getter" when you wrote it, but your naming of it makes it one.

Best bet? Don't use "get" or "set" or "is" prefixes unless you really are making a full property that can be gotten and set. I would also avoid "find" in Domain classes, as that has it's own set of generated methods.

Answer 3

Instead of defining the method as having a return type, try just using def:

class Person {
    String name

    def getSomething(int i) {
        // foo
    }
}

Another solution might be to define something as a transient (providing that you don't actually have a property called 'something'):

class Person {
    String name

    static transients = ['something']

    String getSomething(int i) {
        // foo
    }
}

Answer 4

A couple of notes...

• If you provide a setter, you don't also have to provide a getter. And vice-versa. What you're really doing is overriding the default accessor methods Groovy is attaching for your. You can override one and not the other if you wish.
• There is no problem if you make a method on your domain class starting with 'find' because the dynamic finder methods are actually static method additions (and they all start with 'findBy*').
• The transients solution won't work. Making 'something' a transient value doesn't help the fact that you've got a getter with the wrong parameter signature. Same thing when you dynamically type the return value.
• This is not problem for Groovy, but for Grails.

I think the solution is to change your method name from getSomething to findSomething or whatever you'd like that doesn't go against convention. The following works fine:

class Person {
    String name

    String findSomething(int i) {
    }
}

Answer 5

I've concluded that this is a bug with Grails. I've created GRAILS-3760 which has been fixed in Grails 1.1.2.