Groovy/Grails code cleanup suggestions, please! - grails

Question

I'm new to Groovy & Grails, and I have a feeling that things don't have to be this ugly... so how can I make this code nicer?
This is a Grails controller class, minus some uninteresting bits. Try not to get too hung up that my Car only has one Wheel - I can deal with that later :-)
changeWheel is an Ajax action.
class MyController {
...
def changeWheel = {
if(params['wheelId']) {
def newWheel = Wheel.findById(params['wheelId'])
if(newWheel) {
def car = Car.findById(params['carId'])
car?.setWheel(newWheel)
if(car?.save()) render 'OK'
}
}
}
}

Answer 1

I'd actually start using Command Objects.
Try this:
class MyController {
def index = {
}
def changeWheel = { CarWheelCommand cmd ->
if(cmd.wheel && cmd.car) {
Car car = cmd.car
car.wheel = cmd.wheel
render car.save() ? 'OK' : 'ERROR'
} else {
render "Please enter a valid Car and wheel id to change"
}
}
}
class CarWheelCommand {
Car car
Wheel wheel
}
and then in your view use 'car.id' and 'wheel.id' instead of 'carId' and 'wheelId'

Answer 2

1) pull
params['wheelId']
and
params['carId']
out into their own defs
2) multiple nested ifs is never optimal. You can get rid of the outermost one by having a validateParams method and rendering some sort of response if wheelId and carId are not set. Or just do
if (carId == null || wheelId == null) {
// params invalid
}
3) Assuming everything is ok you could just do
def newWheel = Wheel.findById...
def car = Car.findById...
if (car != null && newWheel != null) {
car.setWheel(newWheel)
car.save()
render 'OK'
} else {
// either wheel or car is null
}
this gets rid of more nested structures...
4) finally, to make the code self documenting, you can do things like assign the conditional tests to appropriately named variables. So something like
def carAndWheelOk = car != null && newWheel != null
if (carAndWheelOk) {
// do the save
} else {
// car or wheel not ok
}
this might be overkill for two tests, but you only are taking care of one wheel here. If you were dealing with all 4 wheels, this type of things increases readability and maintainability.
Note that this advice works in any language. I don't think you can do too much with groovy's syntactic sugar, but maybe some groovy gurus can offer better advice.

Answer 3

There are a couple of things you could do like move some code to a service or command object. But without altering the structure too much, I (subjectively) think the following would make the code easier to read:
use dot notation instead of array indexing to reference params values (params.wheelId instead of params['wheelId'])
I would invert the if to reduce nesting, I think this makes it more clear what the exceptions are.
For example:
if(!params.wheelId) {
sendError(400, "wheelId is required")
return
}
....
....
if(!newWheel) {
sendError(404, "wheel ${params.wheelId} was not found.")
return
}
Now if you don't mind changing the structure and adding more lines of code...
The act of changing the wheel may be a common occurrence across more than just one controller action. In this case I'd recommend putting the GORM/database logic in a Service class. Then your controller only has to verify it has the correct params inputs and pass those on to the Service to do the actual tire changing. A Service method can be transactional, which you'd want in the case where you might have to dismount the old tire before mounting the new one.
In the Service I would throw exceptions for exceptional cases like when a wheel is not found, a car is not found, or if there's an error changing the tire. Then your controller can catch those and respond with the proper HTTP status codes.