Override addTo and removeFrom to listen to changes in an attribute in Grails

Question

I'm new to Grails and I need to make some calculations when a "has-many" attribute changes, and I think the best place to do this is in the setter of the attribute, given that my attribute is a list the best place should be in the addTo and the removeFrom methods, I tried to override them but didn't worked.

So is this the best way of doing it? what's wrong with my code?

Here's the code:

Cicle.groovy

class Cicle {

String machine
int cicleValue

static hasMany = [measurements:Measurement]

static constraints = {
    machine blank:false 
    cicleValue nullable:false 
}

public void addToMeasurements(Measurement measurement){
    super.addToMeasurements(measurement)
    updateCalculations()
}

public void updateCalculations(){

    int sumCicles = 0

    measurements.each{ measurement ->
        sumCicles += measurement.cicleValue
    }

    cicleValue = sumCicles / measurements.size()
    this.save(failOnError: true) 
}
}

This is the exception I get:

No signature of method: com.rpc.mock.app.Cicle.addToMeasurements() is applicable for argument types: (com.rpc.mock.app.Measurement) values: [com.rpc.mock.app.Measurement : (unsaved)]
Possible solutions: addToMeasurements(com.rpc.mock.app.Measurement), addToMeasurements(java.lang.Object), getMeasurements(). Stacktrace follows:
Message: No signature of method: com.rpc.mock.app.Cicle.addToMeasurements() is applicable for argument types: (com.rpc.mock.app.Measurement) values: [com.rpc.mock.app.Measurement : (unsaved)]
Possible solutions: addToMeasurements(com.rpc.mock.app.Measurement), addToMeasurements(java.lang.Object), getMeasurements()
    Line | Method
->>   16 | addToMeasurements in com.rpc.mock.app.Cicle
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
|     43 | $tt__save         in com.rpc.mock.app.MeasurementController
|    200 | doFilter . . . .  in grails.plugin.cache.web.filter.PageFragmentCachingFilter
|     63 | doFilter          in grails.plugin.cache.web.filter.AbstractFilter
|   1145 | runWorker . . . . in java.util.concurrent.ThreadPoolExecutor
|    615 | run               in java.util.concurrent.ThreadPoolExecutor$Worker
^    744 | run . . . . . . . in java.lang.Thread

Thanks

Answer 1

As you're dealing with domain objects, GORM supports the registration of events as methods that get fired when certain events occurs such as deletes, insertsand updates:

beforeInsert - Executed before an object is initially persisted to the database
beforeUpdate - Executed before an object is updated
beforeDelete - Executed before an object is deleted
beforeValidate - Executed before an object is validated
afterInsert - Executed after an object is persisted to the database
afterUpdate - Executed after an object has been updated
afterDelete - Executed after an object has been deleted
onLoad - Executed when an object is loaded from the database

Then, you can add updateCalculations() in your domain object like that:

static constraints = {
    machine blank:false 
    cicleValue nullable:false 
}

def beforeUpdate() { updateCalculations()  }

As a general good design practice, it's better to keep logic implementation out from domains object and Grails allows to inject services into domains (POGO).