(Quick Reference)

7.5.1 Events and Auto Timestamping - Reference Documentation

Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith, Lari Hotari

Version: 3.1.4

7.5.1 Events and Auto Timestamping

GORM supports the registration of events as methods that get fired when certain events occurs such as deletes, inserts and updates. The following is a list of supported events:
  • beforeInsert - Executed before an object is initially persisted to the database. If you return false, the insert will be cancelled.
  • beforeUpdate - Executed before an object is updated. If you return false, the update will be cancelled.
  • beforeDelete - Executed before an object is deleted. If you return false, the delete will be cancelled.
  • beforeValidate - Executed before an object is validated
  • afterInsert - Executed after an object is persisted to the database
  • afterUpdate - Executed after an object has been updated
  • afterDelete - Executed after an object has been deleted
  • onLoad - Executed when an object is loaded from the database

To add an event simply register the relevant method with your domain class.

Do not attempt to flush the session within an event (such as with obj.save(flush:true)). Since events are fired during flushing this will cause a StackOverflowError.

Event types

The beforeInsert event

Fired before an object is saved to the database

class Person {
   private static final Date NULL_DATE = new Date(0)

String firstName String lastName Date signupDate = NULL_DATE

def beforeInsert() { if (signupDate == NULL_DATE) { signupDate = new Date() } } }

The beforeUpdate event

Fired before an existing object is updated

class Person {

def securityService

String firstName String lastName String lastUpdatedBy

static constraints = { lastUpdatedBy nullable: true }

def beforeUpdate() { lastUpdatedBy = securityService.currentAuthenticatedUsername() } }

The beforeDelete event

Fired before an object is deleted.

class Person {
   String name

def beforeDelete() { ActivityTrace.withNewSession { new ActivityTrace(eventName: "Person Deleted", data: name).save() } } }

Notice the usage of withNewSession method above. Since events are triggered whilst Hibernate is flushing using persistence methods like save() and delete() won't result in objects being saved unless you run your operations with a new Session.

Fortunately the withNewSession method lets you share the same transactional JDBC connection even though you're using a different underlying Session.

The beforeValidate event

Fired before an object is validated.

class Person {
   String name

static constraints = { name size: 5..45 }

def beforeValidate() { name = name?.trim() } }

The beforeValidate method is run before any validators are run.

Validation may run more often than you think. It is triggered by the validate() and save() methods as you'd expect, but it is also typically triggered just before the view is rendered as well. So when writing beforeValidate() implementations, make sure that they can handle being called multiple times with the same property values.

GORM supports an overloaded version of beforeValidate which accepts a List parameter which may include the names of the properties which are about to be validated. This version of beforeValidate will be called when the validate method has been invoked and passed a List of property names as an argument.

class Person {
   String name
   String town
   Integer age

static constraints = { name size: 5..45 age range: 4..99 }

def beforeValidate(List propertiesBeingValidated) { // do pre validation work based on propertiesBeingValidated } }

def p = new Person(name: 'Jacob Brown', age: 10) p.validate(['age', 'name'])

Note that when validate is triggered indirectly because of a call to the save method that the validate method is being invoked with no arguments, not a List that includes all of the property names.

Either or both versions of beforeValidate may be defined in a domain class. GORM will prefer the List version if a List is passed to validate but will fall back on the no-arg version if the List version does not exist. Likewise, GORM will prefer the no-arg version if no arguments are passed to validate but will fall back on the List version if the no-arg version does not exist. In that case, null is passed to beforeValidate.

The onLoad/beforeLoad event

Fired immediately before an object is loaded from the database:

class Person {
   String name
   Date dateCreated
   Date lastUpdated

def onLoad() { log.debug "Loading ${id}" } }

beforeLoad() is effectively a synonym for onLoad(), so only declare one or the other.

The afterLoad event

Fired immediately after an object is loaded from the database:

class Person {
   String name
   Date dateCreated
   Date lastUpdated

def afterLoad() { name = "I'm loaded" } }

Custom Event Listeners

As of Grails 2.0 there is a new API for plugins and applications to register and listen for persistence events. This API is not tied to Hibernate and also works for other persistence plugins such as the MongoDB plugin for GORM.

To use this API you need to subclass AbstractPersistenceEventListener (in package org.grails.datastore.mapping.engine.event ) and implement the methods onPersistenceEvent and supportsEventType. You also must provide a reference to the datastore to the listener. The simplest possible implementation can be seen below:

public MyPersistenceListener(final Datastore datastore) {
    super(datastore)
}

@Override protected void onPersistenceEvent(final AbstractPersistenceEvent event) { switch(event.eventType) { case PreInsert: println "PRE INSERT ${event.entityObject}" break case PostInsert: println "POST INSERT ${event.entityObject}" break case PreUpdate: println "PRE UPDATE ${event.entityObject}" break; case PostUpdate: println "POST UPDATE ${event.entityObject}" break; case PreDelete: println "PRE DELETE ${event.entityObject}" break; case PostDelete: println "POST DELETE ${event.entityObject}" break; case PreLoad: println "PRE LOAD ${event.entityObject}" break; case PostLoad: println "POST LOAD ${event.entityObject}" break; } }

@Override public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) { return true }

The AbstractPersistenceEvent class has many subclasses (PreInsertEvent, PostInsertEvent etc.) that provide further information specific to the event. A cancel() method is also provided on the event which allows you to veto an insert, update or delete operation.

Once you have created your event listener you need to register it with the ApplicationContext. This can be done in BootStrap.groovy:

def grailsApplication

def init = { def applicationContext = grailsApplication.mainContext applicationContext.eventTriggeringInterceptor.datastores.each { k, datastore -> applicationContext.addApplicationListener new MyPersistenceListener(datastore) } }

or use this in a plugin:

def doWithApplicationContext = { applicationContext ->
    grailsApplication.mainContext.eventTriggeringInterceptor.datastores.each { k, datastore ->
        applicationContext.addApplicationListener new MyPersistenceListener(datastore)
    }
}

Hibernate Events

It is generally encouraged to use the non-Hibernate specific API described above, but if you need access to more detailed Hibernate events then you can define custom Hibernate-specific event listeners.

You can also register event handler classes in an application's grails-app/conf/spring/resources.groovy or in the doWithSpring closure in a plugin descriptor by registering a Spring bean named hibernateEventListeners. This bean has one property, listenerMap which specifies the listeners to register for various Hibernate events.

The values of the Map are instances of classes that implement one or more Hibernate listener interfaces. You can use one class that implements all of the required interfaces, or one concrete class per interface, or any combination. The valid Map keys and corresponding interfaces are listed here:

NameInterface
auto-flushAutoFlushEventListener
mergeMergeEventListener
createPersistEventListener
create-onflushPersistEventListener
deleteDeleteEventListener
dirty-checkDirtyCheckEventListener
evictEvictEventListener
flushFlushEventListener
flush-entityFlushEntityEventListener
loadLoadEventListener
load-collectionInitializeCollectionEventListener
lockLockEventListener
refreshRefreshEventListener
replicateReplicateEventListener
save-updateSaveOrUpdateEventListener
saveSaveOrUpdateEventListener
updateSaveOrUpdateEventListener
pre-loadPreLoadEventListener
pre-updatePreUpdateEventListener
pre-deletePreDeleteEventListener
pre-insertPreInsertEventListener
pre-collection-recreatePreCollectionRecreateEventListener
pre-collection-removePreCollectionRemoveEventListener
pre-collection-updatePreCollectionUpdateEventListener
post-loadPostLoadEventListener
post-updatePostUpdateEventListener
post-deletePostDeleteEventListener
post-insertPostInsertEventListener
post-commit-updatePostUpdateEventListener
post-commit-deletePostDeleteEventListener
post-commit-insertPostInsertEventListener
post-collection-recreatePostCollectionRecreateEventListener
post-collection-removePostCollectionRemoveEventListener
post-collection-updatePostCollectionUpdateEventListener

For example, you could register a class AuditEventListener which implements PostInsertEventListener, PostUpdateEventListener, and PostDeleteEventListener using the following in an application:

beans = {

auditListener(AuditEventListener)

hibernateEventListeners(HibernateEventListeners) { listenerMap = ['post-insert': auditListener, 'post-update': auditListener, 'post-delete': auditListener] } }

or use this in a plugin:

def doWithSpring = {

auditListener(AuditEventListener)

hibernateEventListeners(HibernateEventListeners) { listenerMap = ['post-insert': auditListener, 'post-update': auditListener, 'post-delete': auditListener] } }

Automatic timestamping

If you define a dateCreated property it will be set to the current date for you when you create new instances. Likewise, if you define a lastUpdated property it will be automatically be updated for you when you change persistent instances.

If this is not the behaviour you want you can disable this feature with:

class Person {
   Date dateCreated
   Date lastUpdated
   static mapping = {
      autoTimestamp false
   }
}

If you have nullable: false constraints on either dateCreated or lastUpdated, your domain instances will fail validation - probably not what you want. Omit constraints from these properties unless you disable automatic timestamping.