Complex Hibernate Projections

Question

I want to ask, it is possible that I create query projections and criterion for more than one level deep? I have 2 model classes:

@Entity  
@Table(name = \"p         


        

Answer 1

I wrote the ResultTransformer, that does this exactly. It's name is AliasToBeanNestedResultTransformer, check it out on github.

Answer 2

AFAIK it is not possible to project more than one level deep with aliastobean transformer. Your options are

• create a flattened Data Transfer Object (DTO)
• fill the resulting Person in memory yourself
• implement your own resulttransformer (similar to option 2)

option 1 looks like this:

Criteria criteria = getHandlerSession().createCriteria(Person.class)
    .createAlias("wife", "wife", JoinType.LEFT.ordinal())
    .add(Restrictions.eq("wife.age", 19)); 
    .setProjection(Projections.projectionList()
        .add(Projections.property("personID"), "personID")
        .add(Projections.property("name"), "personName")
        .add(Projections.property("wife.name"), "wifeName"));
    .setResultTransformer(Transformers.aliasToBean(PersonWifeDto.class));

return criteria.list();

Answer 3

Thanks Sami Andoni. I was able to use your AliasToBeanNestedResultTransformer with a minor modification to suit my situation. What I found was that the nested transformer did not support the scenario where the field is in a super class so I enhanced it to look for fields up to 10 levels deep in the class inheritance hierarchy of the class you're projecting into:

    public Object transformTuple(Object[] tuple, String[] aliases) {

        ...


                if (alias.contains(".")) {
                    nestedAliases.add(alias);

                    String[] sp = alias.split("\\.");
                    String fieldName = sp[0];
                    String aliasName = sp[1];

                    Class<?> subclass = getDeclaredFieldForClassOrSuperClasses(resultClass, fieldName, 1);
...
}

Where getDeclaredFieldForClassOrSuperClasses() is defined as follows:

private Class<?> getDeclaredFieldForClassOrSuperClasses(Class<?> resultClass, String fieldName, int level) throws NoSuchFieldException{
    Class<?> result = null;
    try {
        result = resultClass.getDeclaredField(fieldName).getType();
    } catch (NoSuchFieldException e) {
        if (level <= 10){
        return getDeclaredFieldForClassOrSuperClasses(
                resultClass.getSuperclass(), fieldName, level++);
        } else {
            throw e;
        }
    }
    return result;
}

My Hibernate projection for this nested property looked like this:

Projections.projectionList().add( Property.forName("metadata.copyright").as("productMetadata.copyright"));

and the class I am projecting into looks like this:

public class ProductMetadata extends AbstractMetadata {
...
}

public abstract class AbstractMetadata {
...   
   protected String copyright;
...
}

Answer 4

Instead of creating Data Transfer Object (DTO)
In projectionlist make below changes and it will work for you.

    ProjectionList projections = Projections.projectionList(); 
    projections.add(Projections.property("person.personID"), "personID");
    projections.add(Projections.property("person.wife"), "wife");
    projections.add(Projections.property("wife.name"));

    Criteria criteria = null; 
    criteria = getHandlerSession().createCriteria(Person.class,"person").createAlias("person.wife", "wife"); 
    criterion = Restrictions.eq("wife.age", 19);  
    criteria.add(criterion); 
    criteria.setProjection(projections);
    criteria.setResultTransformer(Transformers.aliasToBean(Person.class)); 
    return criteria.list();