SDN Cypher query with no hits causes a NullPointerException

[Craig Giordano]

I am using SDN 2.1.0.BUILD-SNAPSHOT and Neo4j 1.7.

I have modeled an Activity that has an activityCode and a time range containing a begin and end date.  I need to find the Activity with the latest begin date.  At first I thought, just write a cypher query returning the Activity and begin date as a @MapResult sorting by begin date DESC and grab the first one from the list.  This works fine.  When there are no Activity's I get an empty list back as expected.  Then I thought, a list is silly when I am only interested in the first item so I decided to try the LIMIT key word, ending my query with LIMIT 1.  I changed the signature of my method to return a @MapResult instead of a List and it worked.  Except for the case where there are no satisfying Activity's.  Instead of returning null, I get a NullPointException as follows:

java.lang.NullPointerException
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.extractMapResult(EntityResultConverter.java:85)
    at org.springframework.data.neo4j.support.conversion.EntityResultConverter.convert(EntityResultConverter.java:97)
    at org.springframework.data.neo4j.conversion.QueryResultBuilder$1.convert(QueryResultBuilder.java:102)
    at org.springframework.data.neo4j.conversion.QueryResultBuilder$1.singleOrNull(QueryResultBuilder.java:95)
    at org.springframework.data.neo4j.repository.query.GraphRepositoryQuery.dispatchQuery(GraphRepositoryQuery.java:96)
    at org.springframework.data.neo4j.repository.query.GraphRepositoryQuery.execute(GraphRepositoryQuery.java:70)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:313)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:155)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
    at $Proxy35.findWithLatestBeginByActivityCodeAndTimeRange(Unknown Source)
    at com.ierin.paragon2.domain.repository.ActivityRepositoryTest.canFindActivityByActivityCodeAndTimeRange_BadActivityCode(ActivityRepositoryTest.java:65)

To show some specifics here are two methods with the same cypher query but different behavior when the results are zero:

@Query("start activity=node:DATA_SET_ID_INDEX(dataSetId = {scheduleDataSetId}) " +
            "match activity-[:MODEL_SCHEDULE_ACTIVITY]->plantVariable, activity-[:timeRange]->t " +
            "where plantVariable.dataSetId = {modelDataSetId} " +
            "and activity.activityCode = {activityCode} " +
            "and t.begin < {end} " +
            "and (t.end? is null or t.end > {begin}) " +
            "return activity, t.begin as beginDate order by beginDate desc limit 1")
    ActivityBeginDateResult findWithLatestBeginByActivityCodeAndTimeRange(@Param("modelDataSetId") String modelDataSetId,
                                                                          @Param("scheduleDataSetId") String scheduleDataSetId,
                                                                          @Param("activityCode") String activityCode,
                                                                          @Param("begin") Long begin,
                                                                          @Param("end") Long end);

    @Query("start activity=node:DATA_SET_ID_INDEX(dataSetId = {scheduleDataSetId}) " +
            "match activity-[:MODEL_SCHEDULE_ACTIVITY]->plantVariable, activity-[:timeRange]->t " +
            "where plantVariable.dataSetId = {modelDataSetId} " +
            "and activity.activityCode = {activityCode} " +
            "and t.begin < {end} " +
            "and (t.end? is null or t.end > {begin}) " +
            "return activity, t.begin as beginDate order by beginDate desc limit 1")
    List<ActivityBeginDateResult> findWithLatestBeginByActivityCodeAndTimeRangeInList(@Param("modelDataSetId") String modelDataSetId,
                                                                                      @Param("scheduleDataSetId") String scheduleDataSetId,
                                                                                      @Param("activityCode") String activityCode,
                                                                                      @Param("begin") Long begin,
                                                                                      @Param("end") Long end);

The first method throws the NullPointerException while the second returns an empty List.  Is this a bug or am I misusing the API?

Thanks,
Craig
  

[Lasse Westh-Nielsen]

Craig,

We have captured this bug, please see here to track progress:  https://jira.springsource.org/browse/DATAGRAPH-259 

Regards,

Lasse