Saving associated domain classes in Grails
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22-07-2019 - |
Question
I'm struggling to get association right on Grails. Let's say I have two domain classes:
class Engine {
String name
int numberOfCylinders = 4
static constraints = {
name(blank:false, nullable:false)
numberOfCylinders(range:4..8)
}
}
class Car {
int year
String brand
Engine engine = new Engine(name:"Default Engine")
static constraints = {
engine(nullable:false)
brand(blank:false, nullable:false)
year(nullable:false)
}
}
The idea is that users can create cars without creating an engine first, and those cars get a default engine. In the CarController I have:
def save = {
def car = new Car(params)
if(!car.hasErrors() && car.save()){
flash.message = "Car saved"
redirect(action:index)
}else{
render(view:'create', model:[car:car])
}
}
When trying to save, I get a null value exception on the Car.engine field, so obviously the default engine is not created and saved. I tried to manually create the engine:
def save = {
def car = new Car(params)
car.engine = new Engine(name: "Default Engine")
if(!car.hasErrors() && car.save()){
flash.message = "Car saved"
redirect(action:index)
}else{
render(view:'create', model:[car:car])
}
}
Didn't work either. Is Grails not able to save associated classes? How could I implement such feature?
Solution 2
For what is worth, I finally nailed it.
The exception I got when trying to save a car was
not-null property references a null or transient value
It was obvious that the engine was null when trying to save, but why? Turns out you have to do:
def car = new Car(params)
car.engine = new Engine(name: "Default Engine")
car.engine.save()
Since engine doesn't belongs to a Car, you don't get cascade save/update/delete which is fine in my case. The solution is to manually save the engine and then save the car.
OTHER TIPS
I think you need a belongsTo in your Engine ie
static belongsTo = [car:Car]
Hope this helps.