JPA Criteria Query over an entity hierarchy using single table inheritance

Question

Say I have the following entities:

@Entity
@Inheritance(strategy = SINGLE_TABLE)
@DiscriminatorColumn(name = "type")
public abstract class BaseEntity { 
    private Date someDate;
    private Date otherDate;
    private boolean flag;
}

@Entity
@DiscriminatorValue("entity1")
public class Entity1 extends BaseEntity { 
    private String someProperty;
}

@Entity
@DiscriminatorValue("entity2")
public class Entity2 extends BaseEntity { 
    private String otherProperty;
}

I'm trying to build a criteria query that returns instances of BaseEntity based on properties in BaseEntity and both of the subclasses. So essentially I'm looking for a criteria query that corresponds to this pseudo-SQL:

SELECT * FROM <BaseEntity table name>
WHERE someDate < ? AND otherDate > ? AND flag = ?
AND someProperty = ? AND otherProperty = ?;

I'd rather not build two separate queries since they have so much overlap (ie most of the properties are in the base class). However, I haven't figured out a way to reference the subclass properties in the query if I declare BaseEntity as the root. Is it possible to build a criteria query like this?

UPDATE:

Maybe some code would clarify the question. I'd essentially like to do something like this:

CriteriaBuilder builder = ...;
CriteriaQuery<BaseEntity> query = ...;
Root<BaseEntity> root = ...;

query.select(root).where(builder.and(
        builder.lessThan(root.get(BaseEntity_.someDate), new Date()),
        builder.greaterThan(root.get(BaseEntity_.otherDate), new Date()),
        builder.isTrue(root.get(BaseEntity_.flag)),
        builder.equal(root.get(Entity1_.someProperty), "foo"),   <-- This won't work
        builder.equal(root.get(Entity2_.otherProperty), "bar")   <-- Neither will this
));

Now, I understand why the above code sample doesn't work, but I'd like to know if there's a way to get around it.

Answer 1

I managed to solve this by downcasting the BaseEntity root into new roots that correspond to the subclass types with CriteriaBuilder.treat() like this:

CriteriaBuilder builder = ...;
CriteriaQuery<BaseEntity> query = ...;
Root<BaseEntity> root = ...;
Root<Entity1> entity1 = builder.treat(root, Entity1.class);
Root<Entity2> entity2 = builder.treat(root, Entity2.class);

query.select(root).where(builder.and(
        builder.lessThan(root.get(BaseEntity_.someDate), new Date()),
        builder.greaterThan(root.get(BaseEntity_.otherDate), new Date()),
        builder.isTrue(root.get(BaseEntity_.flag)),
        builder.equal(entity1.get(Entity1_.someProperty), "foo"),
        builder.equal(entity2.get(Entity2_.otherProperty), "bar")
));

Answer 2

Try Junction . You can always do something like this:

Criteria crit = session.createCriteria(YourClassName.class);
Criterion cr1 = Restrictions.lt("propertyname", propertyvalue);
Criterion cr2 = Restrictions.gt("propertyname", propertyvalue);
Criterion cr3 = Restrictions.eq("propertyname", propertyvalue);
Criterion cr4 = Restrictions.eq("propertyname", propertyvalue);
Junction cond = Restrictions.conjunction();
cond.add(cr1).add(cr2).add(cr3).add(cr4)
crit.add(cond);

I hope I got your question Correctly.