Proper Implementation of clone() For Domain Classes to duplicate a Grails domain instance

问题

I have several domain classes for which the user interface includes a "duplicate" command. As part of the implementation of those commands, I have implemented clone() methods in the corresponding domain classes.

I have been trying to correct my bad habit of improperly implementing clone() (in general) based on use of "new" rather than "super.clone()," so as soon as I thought about doing the same for my Grails domain classes, I wondered how using super.clone() to obtain a clone might interact with GORM / Hibernate persistence. In particular, I was wondering about the proper way to handle the implicit "id" property. If I simply super.clone(), do nothing further and later try to save() the cloned instance, will it work properly (creating a new persistence entry?) or will some kind of error or silent failure result?

What is the proper or preferred way to duplicate a Grails domain instance?

回答1:

Add the following method to metaClass of the interface GormInstanceApi which all domain implements it. :

def cloneForDomains={def cloned=delegate.class.newInstance();
                 cloned.properties=delegate.properties;
                return cloned;}

then :

org.grails.datastore.gorm.GormInstanceApi.clone=cloneForDomains ;

Congrats! now you can use clone method such as save , delete .....

USE CASE :

Person p=Person.get(1);
Person cloned=p.clone(); 
 cloned.id=null; 
cloned.save();

UPDATE : you can loop all domain classes also :

grailsApplication.getDomainClasses().each{cls->
             cls.metaClass.clone=cloneForDomains
         }

UPDATE : for deep clone :

  grailsApplication.getDomainClasses().each{cls->
                 cls.metaClass.clone={
                                  return deepClone(delegate);   
                            }
   }

known that deepClone is a method as following:

Object deepClone(domainInstanceToClone) {

         //TODO: PRECISA ENTENDER ISSO! MB-249 no youtrack
         //Algumas classes chegam aqui com nome da classe + _$$_javassist_XX
         if (domainInstanceToClone.getClass().name.contains("_javassist"))
             return null

         //Our target instance for the instance we want to clone
         // recursion
         def newDomainInstance = domainInstanceToClone.getClass().newInstance()

         //Returns a DefaultGrailsDomainClass (as interface GrailsDomainClass) for inspecting properties
         GrailsClass domainClass = domainInstanceToClone.domainClass.grailsApplication.getDomainClass(newDomainInstance.getClass().name)

         def notCloneable = domainClass.getPropertyValue("notCloneable")

         for(DefaultGrailsDomainClassProperty prop in domainClass?.getPersistentProperties()) {
             if (notCloneable && prop.name in notCloneable)
                 continue

             if (prop.association) {

                 if (prop.owningSide) {
                     //we have to deep clone owned associations
                     if (prop.oneToOne) {
                         def newAssociationInstance = deepClone(domainInstanceToClone?."${prop.name}")
                         newDomainInstance."${prop.name}" = newAssociationInstance
                     } else {

                         domainInstanceToClone."${prop.name}".each { associationInstance ->
                             def newAssociationInstance = deepClone(associationInstance)

                             if (newAssociationInstance)
                                 newDomainInstance."addTo${prop.name.capitalize()}"(newAssociationInstance)
                         }
                     }
                 } else {

                     if (!prop.bidirectional) {

                         //If the association isn't owned or the owner, then we can just do a  shallow copy of the reference.
                         newDomainInstance."${prop.name}" = domainInstanceToClone."${prop.name}"
                     }
                     // @@JR
                     // Yes bidirectional and not owning. E.g. clone Report, belongsTo Organisation which hasMany
                     // manyToOne. Just add to the owning objects collection.
                     else {
                         //println "${prop.owningSide} - ${prop.name} - ${prop.oneToMany}"
                         //return
                         if (prop.manyToOne) {

                             newDomainInstance."${prop.name}" = domainInstanceToClone."${prop.name}"
                             def owningInstance = domainInstanceToClone."${prop.name}"
                             // Need to find the collection.
                             String otherSide = prop.otherSide.name.capitalize()
                             //println otherSide
                             //owningInstance."addTo${otherSide}"(newDomainInstance)
                         }
                         else if (prop.manyToMany) {
                             //newDomainInstance."${prop.name}" = [] as Set

                             domainInstanceToClone."${prop.name}".each {

                                 //newDomainInstance."${prop.name}".add(it)
                             }
                         }

                         else if (prop.oneToMany) {
                             domainInstanceToClone."${prop.name}".each { associationInstance ->
                                 def newAssociationInstance = deepClone(associationInstance)
                                 newDomainInstance."addTo${prop.name.capitalize()}"(newAssociationInstance)
                             }
                         }
                     }
                 }
             } else {
                 //If the property isn't an association then simply copy the value
                 newDomainInstance."${prop.name}" = domainInstanceToClone."${prop.name}"

                 if (prop.name == "dateCreated" || prop.name == "lastUpdated") {
                     newDomainInstance."${prop.name}" = null
                 }
             }
         }

         return newDomainInstance
     }

回答2:

I've had much more luck with this method:

YourDomainClass clonedObject = new YourDomainClass(objectToClone.properties)

来源：https://stackoverflow.com/questions/20220711/proper-implementation-of-clone-for-domain-classes-to-duplicate-a-grails-domain