使用标准作为注释的Hibernate / JPA

Question

Does anybody know if it's possible to impose criteria on an object property via annotations. This would be similar to the @Where clause, however the attribute that I need to filter by is not actually on the table the SELECT is performed on since it is mappedBy.

Hopefully this example will illustrate:

public class Container {

  @OneToMany(mappedBy = "container")
  private List<Item> items;

  //getter & setter ...

}

public class Item {

  @ManyToOne
  private Container container;

  @OneToOne(mappedBy = "item")
  private User user;

  //getter & setter ...

}

public class User {

  @OneToOne
  private Item item;

  //getter & setter ...

}

I would like to fetch a Container where there is no User associated. If the user attribute was really on the Item table it should be possible to use @Where:

public class Container {

  @OneToOne(mappedBy = "container")
  @Where(clause = "user is null")
  private List<Item> items;

  //getter & setter ...

}

But since it is mappedBy is there a way of doing this? The join on these tables is obviously already performed in the SQL. Maybe there is a way of referencing the user attribute eg HQL?

Any help much appreciated

Answer 1

In HQL :

select item.container from item i where i.user is null

Container.java

@NamedQueries({
    @NamedQuery(
    name = "findContainerWithNoUser",
    query = "select item.container from item i where i.user is null"
    )
})
@Entity
public class Container {

  @OneToOne(mappedBy = "container")
  private List<Item> items;

  //getter & setter ...

}