Example criteria on alias

mdiaz · **Joined:** Fri Feb 22, 2008 12:45 pm **Posts:** 5

Hi there,

According to the Hibernate documentation, Example queries ignore associations, so if I want to apply an example criteria on an association I should do something like this:

Code:

List results = session.createCriteria(Cat.class)
    .add( Example.create(cat) )
    .createCriteria("mate")
        .add( Example.create( cat.getMate() ) )
    .list();

The problem is that the associated entity ("mate") is retrieved from the database. How can this be avoided?
I just want to filter the root entities with restrictions on their "mate"s but I don't want to retrieve the "mate"s.

Thanks in advance

gonzao_diaz · **Joined:** Mon Nov 26, 2007 2:29 pm **Posts:** 443

MDiaz,

You are mixing a couple of issues in your question. To clarify:
-the example query's purpose is to contain parameters already set, a function that, in your case, we assume the "cat" object has already been created for elsewhere.
-you cannot, on your cat object, place restrictions on the "mate" property simply using cat.mate.propertyA=xxx, assuming mate is a property of cat, of course. You can use this "dot path" notation without need of subcriterias.
-you can ask for specific properties (fields) of Cat instead of the whole object, but if you select the whole object, asking if there is a way to "avoid" the mate to be retrieved is the wrong kind of question.
Hibernate by default connects objects loosely, i.e., using "lazy" associations by default. This means that the mate will not be retrieved by your selection of cats unless you specifically order Hibernate to do so using the "fetch" keyword on your HQL or specify the property retrieval as not lazy.
In other words, "mate" won't be retrieved from your database unless you call "getMate()" case by case, even if "mate" forms part of the "where" clause.

Hablo castellano si te sirve mejor.

mdiaz · **Joined:** Fri Feb 22, 2008 12:45 pm **Posts:** 5

It looks like the Criteria API ignores the lazyness of the associations when restrictions are set for associated entities (as discussed here and here).

The scenario is a Parent entity with a many-to-one (or one-to-one) relationship with a Child entity:

Code:

class Parent {
  private String parentName;
  private Child child;
  // ... getters and setters ...
}

class Child {
  private String childName;
  // ... getters and setters ...
}

If you want to make a Criteria query to retrieve some Parent objects placing restrictions on the Child object(s) you would do it this way:

Code:

List results = session.createCriteria(Parent.class)
    .add( Restrictions.eq("parentName", "John") )
    .createCriteria("child")
        .add( Restrictions.eq("childName", "Paul") )
    .list();

Hibernate eagerly retrieves the Child entities regardless of the laziness of the association in the mapping document.

The workarounds proposed in the threads above have some issues and they don't allow (I think) for Example based queries.

I haven't found any comment about this behavior in the Hibernate docs nor any opened issue regarding this in Hibernate Jira. I think an Issue should be opened for this since the docs are misleading and the behavior seems wrong.

@gonzao_diaz: gracias por el ofrecimiento, pero creo que me apaño con el inglés

Sunil Gupta · **Joined:** Thu Feb 28, 2008 2:06 am **Posts:** 1

I execute the following code

[/img]

Code:

session.createCriteria(Parent.class) 
    .add( Restrictions.eq("parentName", "John") ) 
    .createCriteria("child") 
        .add( Restrictions.eq("childName", "Paul") ) 
    .list();

I get the parent with child as its set in my result.
But the problem is that the childset returned has first element has null and only the second has the details of "Paul".

Any help?