Question

I have an entity class set up in Java, with a many-to-many relationship to another class. However, rather than selecting the entire entity collection, I’d like to select only a property from the child entities. The reason for doing this is that it will lower the amount of data being loaded into the system as I don’t always need the entire entity depending on my view.

This is what I have so far:

@Entity
public class Disposition {
...
    @ManyToMany
    private List<Project> projects;
...
}

This works fine and retrieves a list of Project instances. However, I don’t want to get all the Projects for the Disposition; I only want to retrieve Project.name.

The only solution I’ve been able to come up with so far is using the @Formula annotation but I’d like to avoid this if possible since it requires writing native SQL instead of HQL.

This view is read-only so I don’t expect any changes to the data to be persisted.

Answer 1

you can use hql to only get the child’s name. It would look something like

"select p.name from Project p where p.parent_id = ?"

you would have to tailor the variable names in that, and use a parameterized query to replace the ? with the id of the parent.

It is common to have tailored DAO methods for exactly this sort of situation.