Issues with my criteria query when calling SQL created function

Question

In my Postgres 9.1 database I have a li table that is mapped by ORM (Hibernate) in the following Li class: package a.b; @Entity @Table(name = "li", schema = "public") @TypeDef(name="inet", typeClass=InetType.class) public class Li {

    private long id;
    private Date requestTime;
    private String mac;
    private String username;
    private Serializable srcIp;
    private Serializable dstIp;
    private Short length;
    private Short ipProtocol;
    private Integer srcPort;
    private Integer dstPort;

    //..... ... some other related functions (getters, setters, etc)
}

Now, for being able to create a criteria query for Li entity class, I created its metamodel:

package a.metamodel.b;
@StaticMetamodel(Li.class)
public class Li_ {

    public static volatile SingularAttribute<Li, Long> id;
    public static volatile SingularAttribute<Li, Date> requestDate;
    public static volatile SingularAttribute<Li, String> mac;
    public static volatile SingularAttribute<Li, String> username;
    public static volatile SingularAttribute<Li, Serializable> srcIp;
    public static volatile SingularAttribute<Li, Serializable> dstIp;
    public static volatile SingularAttribute<Li, Short> length;
    public static volatile SingularAttribute<Li, Short> ipProtocol;
    public static volatile SingularAttribute<Li, Integer> srcPort;
    public static volatile SingularAttribute<Li, Integer> dstPort;

}

Because I need to search on li table after hour extracted from requestDate field, I created the following postgres function:

create or replace function public.extract_hour(time_param timestamp with time zone) 
    returns double precision language sql as $function$

    SELECT EXTRACT(hour from $1);            
$function$;

Until now everithing tested and works great. So I started to create my criteria:

EntityManager em = ...
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Li> c = cb.createQuery(Li.class);
Root<Li> l = c.from(Li.class);

//pay attention here
Expression<Double> extractHour = cb.function("extract_hour", Double.class, l.get(Li_.requestDate));
c.where(cb.equal(extractHour, Double.parseDouble(aDynamicHourValue)));
TypedQuery<Li> q = em.createQuery(c);
List<Li> lis = q.getResultList();

When I run the code above I get the following error:

java.lang.NullPointerException
    at org.hibernate.ejb.criteria.path.AbstractPathImpl.get(AbstractPathImpl.java:146)
    ...............

of course, that error comes from that line:

Expression<Double> extractHour = cb.function("extract_hour", Double.class, l.get(Li_.requestDate));

Can anybody help me on solving that issue?

Answer 1

The real problem with my criteria query was the fact that I put Li entity in a package, and its metamodel Li_ on another package. I moved Li_ on the same package with Li and now it seems that this issue is gone.

Answer 2

Not sure but, in your entity the field is named requestTime but in your MetaModel you named it requestDate. I think that MetaModel works with Introspection so maybe your error comes from that Hibernate cannot locate the field named requestDate as it does not exists.