Copy Object Properties to a Map by Value not by Reference - grails

Question

I'm not sure where i'm going wrong, but it seems that I'm not able to copy properties from an object instance and assign them to a map without the values being changed after saving the instance.
This is a sample class:
class Product {
String productName
String proudctDescription
int quantityOnHand
}
Once the form is submitted and it's sent to my controller, I can access the values and manipulate them from the productInstance.properties map that is available from the instance. I want to copy the properties to another map to preserve the values before committing them during an edit. So let's say we are editing a record and these are the values stored in the db: productName = "My Product", productDescription = "My Product Description" and quantityOnHand = 100.
I want to copy them to:
def propertiesBefore = productInstance.properties
This did not work, because when I save the productInstance, the values in propertiesBefore change to whatever the instance had.
So I tried this:
productInstance.properties.each { k,v -> propertiesBefore[k] = v }
Same thing happened again. I am not sure how to copy by value, it seems no matter what I try it copies by reference instead.
EDIT
As per the request of Pawel P., this is the code that I tested:
class Product {
String productName
String productDescription
int quantityOnHand
}
def productInstance = new Product(productName: "Some name", productDescription: "Desciption", quantityOnHand: 10)
def propertiesBefore = [:]
productInstance.properties.each { k,v -> propertiesBefore[k] = (v instanceof Cloneable) ? v.clone() : v }
productInstance.productName = "x"
productInstance.productDescription = "y"
productInstance.quantityOnHand = 9
println propertiesBefore.quantityOnHand // this will print the same as the one after the save()
productInstance.save(flush:true)
println propertiesBefore.quantityOnHand // this will print the same as the one above the save()

Answer 1

Without cloning, copying hash-map [:]'s values to a new hash-map [:]'s space can also be done by "pushing" the first one over, which would achieve the same result that you desired (copy by value)!
def APE = [:]
APE= [tail: 1, body: "hairy", hungry: "VERY!!!"]
def CAVEMAN = [:]
CAVEMAN << APE //push APE to CAVEMAN's space
//modify APE's values for CAVEMAN
CAVEMAN.tail = 0
CAVEMAN.body = "need clothes"
println "'APE': ${APE}"
println "'CAVEMAN': ${CAVEMAN}"
Output ==>
'APE': [tail:1, body:hairy, hungry:VERY!!!]
'CAVEMAN': [tail:0, body:need clothes, hungry:VERY!!!]

Answer 2

The problem is that you actually copy references to variables. To obtain copy of variable you should use clone(). Take a look:
class Product {
String productName
String productDescription
int quantityOnHand
}
def productInstance = new Product(productName: "Some name", productDescription: "Desciption", quantityOnHand: 10)
def propertiesBefore = [:]
productInstance.properties.each { k,v -> propertiesBefore[k] = (v instanceof Cloneable) ? v.clone() : v }
productInstance.productName = "x"
productInstance.productDescription = "y"
productInstance.quantityOnHand = 9
println productInstance.properties
println propertiesBefore
It prints:
[quantityOnHand:9, class:class Product, productName:x, productDescription:y]
[quantityOnHand:10, class:class Product, productName:Some name, productDescription:Desciption]

Answer 3

A simpler example for groovy using Hash-Map [:] can be like this:
def APE = [:]
APE= [tail: 1, body: "hairy", hungry: "VERY!!!"]
def CloneMe = APE //*APE as clone*
def CAVEMAN = [:] //*copy APE's values over thru mapping the clone*
CloneMe.each { key,value -> CAVEMAN[key] = (value instanceof Cloneable) ? value.clone() : value }
println "'CloneMe': ${CloneMe}"
//change some of the clone's values for CAVEMAN
CAVEMAN.tail = 0
CAVEMAN.body = "need clothes"
println "'APE': ${APE}"
println "'CAVEMAN': ${CAVEMAN}"
Output ==>
'CloneMe': [tail:1, body:hairy, hungry:VERY!!!]
'APE': [tail:1, body:hairy, hungry:VERY!!!]
'CAVEMAN': [tail:0, body:need clothes, hungry:VERY!!!]