Hibernate – JPA + Hibernate count(*) using CriteriaBuilder – with generatedAlias

criteria-apihibernatejpa

When trying to create a count(*) type query using CriteriaBuilder I get the below alias problem.

What changes should I make to the code below to get the count?

Constraints:

I have to use CriteriaBuilder/Query as the where clause has to be built dynamically based on values.
I need only COUNT, not the list of objects in memory.

Code sample snippet:

 Class<ReqStatCumulative> entityClass = ReqStatCumulative.class;
 @Override
    public long getCountForAlertConfig(AlertConfig cfg) {
        long count = 0L;
        if (null != cfg) {
            CriteriaBuilder qb = entityManager.getCriteriaBuilder();

            Metamodel model = entityManager.getMetamodel();
            EntityType<ReqStatCumulative> reqStatEntType_ = model.entity(entityClass);
            CriteriaQuery<ReqStatCumulative> cq = qb.createQuery(entityClass);
            Root<ReqStatCumulative> rootReqStatEnt = cq.from(reqStatEntType_);
            Path<Long> processTimeSeconds = rootReqStatEnt.<Long> get("processTimeSeconds");
            cq.where(qb.and(qb.greaterThan(processTimeSeconds, (long) cfg.getProcessTimeExceedsSec()),//
                    qb.lessThan(processTimeSeconds, (long) cfg.getProcessTimeExceedsSec() + 100))//
            );//
            findCountByCriteria(entityManager, cq, qb);
            log.debug("\n\t#####Alert desc:" + cfg.getDescription());
            log.debug("\n\t#####Alert count= " + count);
        } else {
            // Do nothing
        }
        return count;
    }

    public <T> Long findCountByCriteria(EntityManager em, CriteriaQuery<T> cqEntity, CriteriaBuilder qb) {
        CriteriaBuilder builder = qb;
        CriteriaQuery<Long> cqCount = builder.createQuery(Long.class);
        Root<?> entityRoot = cqCount.from(cqEntity.getResultType());
        cqCount.select(builder.count(entityRoot));
        cqCount.where(cqEntity.getRestriction());
        return em.createQuery(cqCount).getSingleResult();
    }

Log: I want generatedAlias0 to be used in all the where clause attributes instead of generatedAlias1.

select count(*) from abc.domain.ReqStatCumulative as **generatedAlias0** where ( **generatedAlias1**.processTimeSeconds>5L ) and ( **generatedAlias1**.processTimeSeconds<200L )

10:48:57.169 [main] DEBUG o.h.h.i.ast.QueryTranslatorImpl - parse() - HQL: select count(*) from abc.domain.ReqStatCumulative as generatedAlias0 where ( generatedAlias1.processTimeSeconds>5L ) and ( generatedAlias1.processTimeSeconds<200L )
10:48:57.169 [main] DEBUG o.h.h.i.ast.QueryTranslatorImpl - --- HQL AST ---
 \-[QUERY] Node: 'query'
    +-[SELECT_FROM] Node: 'SELECT_FROM'
    |  +-[FROM] Node: 'from'
    |  |  \-[RANGE] Node: 'RANGE'
    |  |     +-[DOT] Node: '.'
    |  |     |  +-[DOT] Node: '.'
    |  |     |  |  +-[IDENT] Node: 'abc'
    |  |     |  |  \-[IDENT] Node: 'domain'
    |  |     |  \-[IDENT] Node: 'ReqStatCumulative'
    |  |     \-[ALIAS] Node: '**generatedAlias0**'
    |  \-[SELECT] Node: 'select'
    |     \-[COUNT] Node: 'count'
    |        \-[ROW_STAR] Node: '*'
    \-[WHERE] Node: 'where'
       \-[AND] Node: 'and'
          +-[GT] Node: '>'
          |  +-[DOT] Node: '.'
          |  |  +-[IDENT] Node: '**generatedAlias1**'
          |  |  \-[IDENT] Node: 'processTimeSeconds'
          |  \-[NUM_LONG] Node: '5L'
          \-[LT] Node: '<'
             +-[DOT] Node: '.'
             |  +-[IDENT] Node: '**generatedAlias1**'
             |  \-[IDENT] Node: 'processTimeSeconds'
             \-[NUM_LONG] Node: '200L'

10:48:57.169 [main] DEBUG o.h.hql.internal.ast.ErrorCounter - throwQueryException() : no errors
10:48:57.169 [main] DEBUG o.h.h.i.antlr.HqlSqlBaseWalker - select << begin [level=1, statement=select]
10:48:57.169 [main] DEBUG o.h.h.internal.ast.tree.FromElement - FromClause{level=1} : erf.domain.ReqStatCumulative (generatedAlias0) -> reqstatcum0_
10:48:57.169 [main] ERROR o.h.hql.internal.ast.ErrorCounter -  Invalid path: 'generatedAlias1.processTimeSeconds'
10:48:57.215 [main] ERROR o.h.hql.internal.ast.ErrorCounter -  Invalid path: 'generatedAlias1.processTimeSeconds'
org.hibernate.hql.internal.ast.InvalidPathException: Invalid path: 'generatedAlias1.processTimeSeconds'

Best Answer

Your code fails because you are using different Root instances for the count and the where clauses: the first one (in order of definition) generates generatedAlias1 alias, and the other generates generatedAlias0. You need to refactor the code in order to use the same Root instance in both places:

CriteriaQuery<Long> cqCount = builder.createQuery(Long.class);
Root<ReqStatCumulative> entityRoot = cqCount.from(cqEntity.getResultType());
cqCount.select(builder.count(entityRoot));
Path<Long> processTimeSeconds = entityRoot.get("processTimeSeconds");
cqCount.where(qb.and(qb.greaterThan(processTimeSeconds, (long) cfg.getProcessTimeExceedsSec()),//
                qb.lessThan(processTimeSeconds, (long) cfg.getProcessTimeExceedsSec() + 100))//
                );//    
return em.createQuery(cqCount).getSingleResult();

Related Solutions

Java – What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do

From the community documentation:

hibernate.hbm2ddl.auto Automatically validates or exports schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly.

e.g. validate | update | create | create-drop

So the list of possible options are,

validate: validate the schema, makes no changes to the database.
update: update the schema.
create: creates the schema, destroying previous data.
create-drop: drop the schema when the SessionFactory is closed explicitly, typically when the application is stopped.
none: does nothing with the schema, makes no changes to the database

These options seem intended to be developers tools and not to facilitate any production level databases, you may want to have a look at the following question; Hibernate: hbm2ddl.auto=update in production?

JPA EntityManager: Why use persist() over merge()

Either way will add an entity to a PersistenceContext, the difference is in what you do with the entity afterwards.

Persist takes an entity instance, adds it to the context and makes that instance managed (ie future updates to the entity will be tracked).

Merge returns the managed instance that the state was merged to. It does return something what exists in PersistenceContext or creates a new instance of your entity. In any case, it will copy the state from the supplied entity, and return managed copy. The instance you pass in will not be managed (any changes you make will not be part of the transaction - unless you call merge again). Though you can use the returned instance (managed one).

Maybe a code example will help.

MyEntity e = new MyEntity();

// scenario 1
// tran starts
em.persist(e); 
e.setSomeField(someValue); 
// tran ends, and the row for someField is updated in the database

// scenario 2
// tran starts
e = new MyEntity();
em.merge(e);
e.setSomeField(anotherValue); 
// tran ends but the row for someField is not updated in the database
// (you made the changes *after* merging)
      
// scenario 3
// tran starts
e = new MyEntity();
MyEntity e2 = em.merge(e);
e2.setSomeField(anotherValue); 
// tran ends and the row for someField is updated
// (the changes were made to e2, not e)

Scenario 1 and 3 are roughly equivalent, but there are some situations where you'd want to use Scenario 2.

Best Answer

Related Solutions

Java – What are the possible values of the Hibernate hbm2ddl.auto configuration and what do they do

JPA EntityManager: Why use persist() over merge()

Related Topic