grails NullPointerException saving bi-directional one-to-many relationship model - json

Question

I have the following two simple models creating a bidirectional one-to-many relationship in a Grails 2.4.3 application:
class Player {
String firstName
String lastName
String position
static belongsTo = [team: Team]
}
class Team {
String name
List players = new ArrayList()
static hasMany = [players: Player]
static mapping= {
players cascade:"all-delete-orphan"
}
}
I would like to be able to save and update teams and their associated players via nested JSON, like so:
{
name : "team A",
players : [
{
firstName : "john",
lastName :"doe",
position : "center"
}
]
}
My TeamController save action looks like this:
def save() {
def team = new Team(request.JSON)
team.save()
respond team
}
When I make a request with that JSON, I get an error:
curl -X POST -d '{name:"team a",players:[{firstName:"john",lastName:"doe",position:"center"}]}' http://localhost:8080/team-test/team/save.json --header "Content-Type:application/json"
Produces this output in console:
| Error 2014-11-14 10:32:26,111 [http-bio-8080-exec-6] ERROR errors.GrailsExceptionResolver - NullPointerException occurred when processing request: [POST] /team-test/team/save.json
Stacktrace follows:
Message: null
Line | Method
->> 8 | save in team.test.TeamController$$EOvbjH0K
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| 198 | doFilter in grails.plugin.cache.web.filter.PageFragmentCachingFilter
| 63 | doFilter in grails.plugin.cache.web.filter.AbstractFilter
| 1145 | runWorker in java.util.concurrent.ThreadPoolExecutor
| 615 | run . . . in java.util.concurrent.ThreadPoolExecutor$Worker
^ 745 | run in java.lang.Thread
Because that's a rather vague message, I put a try/catch around the team.save() call in the TeamController and print out the stack trace:
def save() {
def team = new Team(request.JSON)
try {
team.save()
}
catch(Exception e)
{
e.printStackTrace()
}
respond team
}
Error java.lang.NullPointerException
| Error at org.hibernate.engine.spi.BatchFetchQueue.removeBatchLoadableEntityKey(BatchFetchQueue.java:163)
| Error at org.hibernate.engine.internal.StatefulPersistenceContext.addEntity(StatefulPersistenceContext.java:388)
| Error at org.hibernate.engine.internal.StatefulPersistenceContext.addEntity(StatefulPersistenceContext.java:461)
| Error at org.hibernate.action.internal.AbstractEntityInsertAction.makeEntityManaged(AbstractEntityInsertAction.java:143)
| Error at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:201)
| Error at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:179)
| Error at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:214)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:324)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:288)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:194)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:209)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:194)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:114)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
| Error at org.hibernate.internal.SessionImpl.fireSaveOrUpdate(SessionImpl.java:684)
| Error at org.hibernate.internal.SessionImpl.saveOrUpdate(SessionImpl.java:676)
| Error at org.hibernate.engine.spi.CascadingActions$5.cascade(CascadingActions.java:235)
| Error at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:350)
| Error at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:293)
| Error at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:161)
| Error at org.hibernate.engine.internal.Cascade.cascadeCollectionElements(Cascade.java:379)
| Error at org.hibernate.engine.internal.Cascade.cascadeCollection(Cascade.java:319)
| Error at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:296)
| Error at org.hibernate.engine.internal.Cascade.cascadeProperty(Cascade.java:161)
| Error at org.hibernate.engine.internal.Cascade.cascade(Cascade.java:118)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:460)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:294)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:194)
| Error at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:209)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:194)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:114)
| Error at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:90)
| Error at org.hibernate.internal.SessionImpl.fireSaveOrUpdate(SessionImpl.java:684)
| Error at org.hibernate.internal.SessionImpl.saveOrUpdate(SessionImpl.java:676)
| Error at org.hibernate.internal.SessionImpl.saveOrUpdate(SessionImpl.java:671)
| Error at org.codehaus.groovy.grails.orm.hibernate.metaclass.SavePersistentMethod$1.doInHibernate(SavePersistentMethod.java:58)
| Error at org.codehaus.groovy.grails.orm.hibernate.GrailsHibernateTemplate.doExecute(GrailsHibernateTemplate.java:179)
| Error at org.codehaus.groovy.grails.orm.hibernate.GrailsHibernateTemplate.execute(GrailsHibernateTemplate.java:123)
| Error at org.codehaus.groovy.grails.orm.hibernate.metaclass.SavePersistentMethod.performSave(SavePersistentMethod.java:56)
| Error at org.codehaus.groovy.grails.orm.hibernate.metaclass.AbstractSavePersistentMethod.doInvokeInternal(AbstractSavePersistentMethod.java:215)
| Error at org.codehaus.groovy.grails.orm.hibernate.metaclass.AbstractDynamicPersistentMethod.invoke(AbstractDynamicPersistentMethod.java:68)
| Error at org.codehaus.groovy.grails.orm.hibernate.HibernateGormInstanceApi.save(HibernateGormInstanceApi.groovy:156)
| Error at team.test.Team$$EOvbjH0K.save(Team.groovy)
| Error at team.test.Team$$DOvbjH0K.save(Unknown Source)
| Error at team.test.Team.save(Team.groovy)
| Error at team.test.Team$save.call(Unknown Source)
| Error at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
| Error at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
| Error at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:112)
| Error at team.test.TeamController$$EOvbkj0y.save(TeamController.groovy:9)
| Error at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
| Error at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
| Error at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
| Error at java.lang.reflect.Method.invoke(Method.java:606)
| Error at org.springsource.loaded.ri.ReloadedTypeInvoker$2.invoke(ReloadedTypeInvoker.java:122)
| Error at org.springsource.loaded.ri.ReflectiveInterceptor.jlrMethodInvoke(ReflectiveInterceptor.java:1299)
| Error at org.codehaus.groovy.grails.web.servlet.mvc.MixedGrailsControllerHelper.invoke(MixedGrailsControllerHelper.java:154)
| Error at org.codehaus.groovy.grails.web.servlet.mvc.AbstractGrailsControllerHelper.handleAction(AbstractGrailsControllerHelper.java:375)
| Error at org.codehaus.groovy.grails.web.servlet.mvc.AbstractGrailsControllerHelper.executeAction(AbstractGrailsControllerHelper.java:252)
| Error at org.codehaus.groovy.grails.web.servlet.mvc.AbstractGrailsControllerHelper.handleURI(AbstractGrailsControllerHelper.java:205)
| Error at org.codehaus.groovy.grails.web.servlet.mvc.AbstractGrailsControllerHelper.handleURI(AbstractGrailsControllerHelper.java:126)
| Error at org.codehaus.groovy.grails.web.servlet.mvc.SimpleGrailsController.handleRequest(SimpleGrailsController.java:72)
| Error at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:50)
| Error at org.codehaus.groovy.grails.web.servlet.GrailsDispatcherServlet.doDispatch(GrailsDispatcherServlet.java:347)
| Error at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
| Error at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
| Error at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
| Error at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
| Error at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
| Error at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at grails.plugin.cache.web.filter.PageFragmentCachingFilter.doFilter(PageFragmentCachingFilter.java:198)
| Error at grails.plugin.cache.web.filter.AbstractFilter.doFilter(AbstractFilter.java:63)
| Error at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344)
| Error at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:748)
| Error at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:486)
| Error at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:411)
| Error at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:338)
| Error at org.codehaus.groovy.grails.web.mapping.UrlMappingUtils.forwardRequestForUrlMappingInfo(UrlMappingUtils.java:178)
| Error at org.codehaus.groovy.grails.web.mapping.UrlMappingUtils.forwardRequestForUrlMappingInfo(UrlMappingUtils.java:144)
| Error at org.codehaus.groovy.grails.web.mapping.UrlMappingUtils.forwardRequestForUrlMappingInfo(UrlMappingUtils.java:135)
| Error at org.codehaus.groovy.grails.web.mapping.filter.UrlMappingsFilter.doFilterInternal(UrlMappingsFilter.java:216)
| Error at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.codehaus.groovy.grails.web.servlet.mvc.GrailsWebRequestFilter.doFilterInternal(GrailsWebRequestFilter.java:69)
| Error at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.codehaus.groovy.grails.web.filters.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:67)
| Error at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
| Error at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
| Error at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344)
| Error at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261)
| Error at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
| Error at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
| Error at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
| Error at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
| Error at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
| Error at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
| Error at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
| Error at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
| Error at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
| Error at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
| Error at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
| Error at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
| Error at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
| Error at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
| Error at java.lang.Thread.run(Thread.java:745)
For further investigation, I put some logging in the controller action to see what's going on within the object:
def save() {
JSON.use('deep')
def team = new Team(request.JSON)
println "errors? " + team.getErrors()
println "team: " + team.toString()
println ((team as JSON).toString())
respond team
}
which produces the following output:
errors? grails.validation.ValidationErrors: 0 errors
team: team.test.Team : (unsaved)
{
"class":"team.test.Team",
"id":null,
"name":"team a",
"players":[
{
"class":"team.test.Player",
"id":null,
"firstName":"john",
"lastName":"doe",
"position":"center",
"team":null
}
]
}
Is there something wrong with my JSON? Why do I get this error? Is it because the team reference is null in the player object? Why is the team reference null in the player object?
Out of curiosity, I removed the belongsTo property from the Player class, and things work as expected...
{"class":"team.test.Team","id":2,"name":"team a","players":[{"class":"team.test.Player","id":2}]}
Why does it not work in the bidirectional case? What are the different implications of bidirectional and unidirectional in terms of table relationships, data binding, etc? I understand the different cascade strategies when using belongsTo or not in a one-to-many relationship, but both should cascade saves I thought.
I know I'm asking many questions. I need help making this work but would also like to understand what is happening in principle. Help is much appreciated.
edit:
per #th3morg's suggestion I attempted manually building out the Team and Player models and associating them via Team.addToPlayers().
def save() {
JSON.use('deep')
def teamData = request.JSON
def team = new Team()
team.name = teamData.name
teamData.players.each { playerData ->
def player = new Player(playerData)
team.addToPlayers(player)
}
team.save()
println ((team as JSON).toString())
respond team
}
produces:
{"class":"team.test.Team","id":3,"name":"team a","players":[{"class":"team.test.Player","id":3,"firstName":"john","lastName":"doe","position":"center","team":{"_ref":"../..","class":"team.test.Team"}}]}
This appears to work, but it is verbose and fragile. Is there no way to achieve the same result through automatic binding or through some other conventional magic?

Answer 1

I think in your case, the reason is straightforward - you need to explicitly call team.addToPlayers(player) before you save. I'm guessing that instantiating a team with the JSON constructor is equivalent to the Map constructor, which is basically equivalent to doing the following:
def team = new Team()
team.players = [new Player(), new Player()]
team.save()
i.e. setting the players properly directly, rather than calling addToPlayers.
If you run this in a test app, you will get exactly the same exception as you received in your version. This is because (as you've recognized), each Player does not have a back-reference to the Team set (which is what team.addToPlayers()) does. This (strangely) still saves the player object because the Hibernate session flushes when the controller finishes, saving any unsaved instances.
I'd be surprised if removing belongsTo property from the Player class actually fixes the issue - did it actually persist the TeamPlayers relationship? Or did it just look like it worked because you were responding with a JSON object where you had effectively manually set the players property?
I realize this is over a year old now, but the reason why I'm commenting is to leave a note for others : there is a (possibly related) known Grails bug which throws the same exception with multiple cascading relationships (e.g. A -> hasMany -> B hasMany -> C) where a child/grandchild has a beforeInsert() or beforeUpdate() method. This may be fixed in Grails 3.x but looks like it will not be fixed in 2.x. - see here and here.

Answer 2

You may be able to fix this with a beforeSave() function within your Team domain where you iterate over the players and save each player. This should avoid hibernate trying to save the transient player objects and also prevent you from having to code it yourself in the controller, which is a bit odd feeling.
Also, using GSON, you might be able to avoid any of the addTo associations hibernate would want.
https://github.com/robfletcher/grails-gson#readme