Grails Overriding domain.addTo - grails

Question

I'd like to do some work when a new object is added to a domain with a hasMany relationship.
like for example, for a Person hasMany Hobby do some work in the interceptor for addToHobby() and removeFromHobby() as follows:
class Person {
String name
boolean likesFishing
static hasMany = [hobby: Hobby]
addToHobby(Hobby h) {
super.addToHobby(h) //*throws missingMethod exception
if (h.name="Fishing") {this.likesFishing=true;}
}
removeFromHobby(Hobby h) {
super removeFromHobby(h)
if (h.name="Fishing") {this.likesFishing=false;}
}
}
For some reason an error is thrown which I guess has something to do with some magic work being done by Gorm that isn't done when the method is overridden. Anyway around this? I can put this kind of thing in beforeUpdate or something like that, but that's a lot more general and will catch every update, not just an addition or removal from the list.
Note the error thrown is not the null pointer exception referred to in the post on this topic 7 years ago (apparently caused by faiilure to initiate the Set), but rather a InvocationTargetException preventing the super method from beeing called.
No signature of method: testapp.Person.addToHobby() is applicable for argument types: (testapp.Hobby) values: [testapp.Hobby : (unsaved)]
Possible solutions: addToHobby(testapp.Hobby), addToHobby(java.lang.Object), getHobby(). Stacktrace follows:
java.lang.reflect.InvocationTargetException: null
at org.grails.core.DefaultGrailsControllerClass$ReflectionInvoker.invoke(DefaultGrailsControllerClass.java:210)
at org.grails.core.DefaultGrailsControllerClass.invoke(DefaultGrailsControllerClass.java:187)
at org.grails.web.mapping.mvc.UrlMappingsInfoHandlerAdapter.handle(UrlMappingsInfoHandlerAdapter.groovy:90)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at org.springframework.boot.web.filter.ApplicationContextHeaderFilter.doFilterInternal(ApplicationContextHeaderFilter.java:55)
at org.grails.web.servlet.mvc.GrailsWebRequestFilter.doFilterInternal(GrailsWebRequestFilter.java:77)
at org.grails.web.filters.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:67)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

Answer 1

The domain methods are injected into your classes by meta-programming or similar technique, so there's no such thing as super.addTo*().
The easiest way for you would be to use interceptors as you mentioned, or you can add your own meta-methods to override GORM's default addTo's.
For example:
class BootStrap {
def init = { servletContext ->
def oldAddToHobby = Person.metaClass.getMetaMethod 'addToHobby'
Person.metaClass.addToHobby{ Hobby h ->
oldAddToHobby.invoke delegate, h
println 'blah 2'
}
}
def destroy = {}
}

Answer 2

Based on injecteer's comment above, below is a generic method to add a handler after addTo (or any other dynamic method which takes a single parameter).
public class Meta {
static boolean setAfterHandler(String methodName, Class sourceClass, Class paramClass) {
//get the method
MetaMethod mymethod = sourceClass.metaClass.getMetaMethod(methodName)
if (mymethod==null) return false
//if after_ handler exists, update the metaClass to call the
// dynamic method, and then the after_ method handler. r
if (sourceClass.newInstance().respondsTo("after_${methodName}")) {
sourceClass.metaClass."${methodName}" {myParam ->
mymethod.invoke delegate, myParam
delegate."after_${methodName}"(myParam);
}
return true
} else {
return false
}
}
To use this, call the setAfterHandler method somewhere in Bootstrap or elsewhere before you try to use it, for example
def success = Meta.setAfterHandler("addToHobby", Person.class, Hobby.class)
In your domain class, insert your handler with the method name after_addToCollectionName as in the example below:
class Person {
String first
String last
Integer age
boolean likesFishing=false
static hasMany = [hobby: Hobby]
static constraints = {
}
void after_addToHobby(Hobby h) {
if (h.name=="Fishing") {
this.likesFishing=true;
}
}
}

Answer 3

You'll probably have more fun attacking this problem from the other side:...
class Hobby {
String name
static belongsTo = [person: Person]
setPerson(Person p) {
this.person = p
if (name="Fishing") {p.likesFishing=true;}
}
Person getPerson() {
return this.person
}
}