Performing an operation on a "hasMany" object when inserting it a new item in grails

Question

I'm new in Grails and I'm creating my first app and I'm having a little trouble finding where things happen, so, I have an object "cicle" that has many "measurements" and gets created by the measurement controller each time I create a new "measurement" that a different machine, this happens for the same machine, some properties of cicle change, so, I execute a method in cicle called updateCalculations that needs the data of the newly created measurement.

So in the measurementController I´m trying to perform some operations using measurements from cycle but I get a null pointer exception, I guessed cicle wasn't created so I moved the operation to the method afterInsert in Measurement object a place I thougth was better for this method to be invoqued, but I'm getting the same problem there, I even think cicle is created buy measurements some how isn't initialized, I don't know really whats happening, so can you help me?

this is my code:

Measurement.groovy

class Measurement{

String machine
int time1
int time2
int time3
int cicleValue

static belongsTo = [cicle: Cicle]

static constraints = {
    machine blank:false 
    time1 nullable:false 
    time1 min:0 
    time2 nullable:false
    time2 min:0
    time3 nullable:false
    time3 min:0
    cicleValue nullable:false
    cicleValue min:0  
}

def afterInsert(){
    this.cicle.updateCalculations()
}

public void updateCicleValue(){
    double avgTime = (time1 + time2 + time3)/3
    cicleValue = 30 * 24 * 60 * 60 / avgTime
}
}

Cicle.groovy

class Cicle {

String machine
int cicleValue

static hasMany = [measurements:Measurement]

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

public void updateCalculations(){

    int sumCicles = 0

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

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

MeasurementController.groovy

@Transactional(readOnly = true)
class MeasurementController {

static allowedMethods = [save: "POST", update: "PUT", delete: "DELETE"]

def create() {
    respond new Measurement(params)
}

@Transactional
def save(Measurement measurementInstance) {
if (measurementInstance == null) {
        notFound()
        return
    }

measurementInstance.updateCicleValue()

    Cicle cicle = Cicle.findByMachine(measurementInstance.machine)

    if(cicle == null){
        cicle = new Cicle(machine: measurementInstance.machine, cicleValue: measurementInstance.cicleValue)
        cicle.save flush: true
    } 

    measurementInstance.cicle = cicle

    measurementInstance.validate()

    if (measurementInstance.hasErrors()) {
        respond measurementInstance.errors, view:'create'
        return
    }

    measurementInstance.save flush:true
    cicle.measurements << measurementInstance
    cicle.save flush: true

    request.withFormat {
        form multipartForm {
            flash.message = message(code: 'default.created.message', args: [message(code: 'measurementInstance.label', default: 'Measurement'), measurementInstance.id])
            redirect measurementInstance
        }
        '*' { respond measurementInstance, [status: CREATED] }
    }
}

protected void notFound() {
    request.withFormat {
        form multipartForm {
            flash.message = message(code: 'default.not.found.message', args: [message(code: 'measurementInstance.label', default: 'Measurement'), params.id])
            redirect action: "index", method: "GET"
        }
        '*'{ render status: NOT_FOUND }
    }
}
}

Here is the stack-trace from the console:

|Loading Grails 2.3.7
|Configuring classpath
.
|Environment set to development
.................................
|Packaging Grails application
...........
|Compiling 1 source files
...............................
|Running Grails application
|Server running. Browse to http://localhost:8080/mock-app
....Error 
|
2014-04-24 21:51:34,719 [http-bio-8080-exec-3] ERROR errors.GrailsExceptionResolver  - NullPointerException occurred when processing request: [POST] /mock-app/measurement/save - parameters:
time3: 20
time2: 20
time1: 20
machine: 2-12
create: Crear
Cannot invoke method size() on null object. Stacktrace follows:
Message: Cannot invoke method size() on null object
    Line | Method
->>   23 | updateCalculations in com.rpc.mock.app.Cicle
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
|     26 | afterInsert        in com.rpc.mock.app.Measurement
|    153 | call . . . . . . . in org.grails.datastore.gorm.support.EventTriggerCaller$MethodCaller
|     96 | call               in org.grails.datastore.gorm.support.EventTriggerCaller
|     47 | onApplicationEvent in org.grails.datastore.mapping.engine.event.AbstractPersistenceEventListener
|     51 | $tt__save          in com.rpc.mock.app.MeasurementController
|    200 | doFilter . . . . . in grails.plugin.cache.web.filter.PageFragmentCachingFilter
|     63 | doFilter           in grails.plugin.cache.web.filter.AbstractFilter
|   1145 | runWorker . . . .  in java.util.concurrent.ThreadPoolExecutor
|    615 | run                in java.util.concurrent.ThreadPoolExecutor$Worker
^    744 | run . . . . . . .  in java.lang.Thread

it stops in the afterUpdate method telling measurements its null

Any help would be great

Thanks

Answer 1

This is beacause you forgot to add measurementInstance to the cicle.measurements. Have a try and add it when saving cicle instance here:

 if(cicle == null){
        cicle = new Cicle(machine: measurementInstance.machine, cicleValue: measurementInstance.cicleValue)
        cicle.addToMeasurements(measurementInstance)    //add to collection
        cicle.save flush: true
    }