使用Hibernate 3查询多对一属性

Question

Java / Hibernate-3. I have an object called "Ticket", and it has a many-to-one association to "Person". This is mapped as:

<class name="Ticket"> 
   ...
   <many-to-one name="person" class="Person" ...>
   ...
</class>

I want to query for Tickets, and limit my results by a property on Person. I'd like to list all Tickets which have assigned_to = 'ADMIN' or person.role = 'ADMIN' . I was expecting to be able to do something like this:

        query.add(
            Expression.or(
                Expression.eq("assigned_to", "ADMIN"),
                Expression.eq("person.role", "ADMIN")
            )
        );

But I get an error: could not resolve property: person.role of: model.Ticket

How can I query for Ticket , restricting results based on Ticket.Person.role ?

Answer 1

You need to create an Alias for the second table first:

List tickets = sess.createCriteria(Ticket.class)
    .createAlias("person", "p")
    .add( Restrictions.eqProperty("p.role", "ADMIN") )
    .list();

By setting the alias you can refer to the second table. If you don't explicitly set the alias, Hibernate will create its own alias. And you eq("person.role", "ADMIN") isn't using that alias correctly, so you have an invalid query. By explicitly setting the alias yourself, you know the alias and can refer to it correctly.

Answer 2

You can do it easily enough using the criteria API, as in 15.4. Criteria Queries - Associations of the Hibernate 3.2 manual. The key point is that you need to define another criteria for the Ticket->Person association, and then apply the filter to that. Alternatively, define an alias, as per that link.

It's hard to give you a code sample, since your original sample is so brief there's not much context.