Finding beans using entity manager

bhaal · **Posted:** Fri Nov 17, 2006 9:48 am

I have tables material, attribute and material_attribute (one-to-many - material-attributes) associacion.
Attribute have columns id, name, value.
Material_attribute have columns material_id, attribute_id.
Material have column id.
I can get attributes by material.getAttributes()

Question is:

How to find bean attribute using EntityManager em.find(Attribute.class, if I know material_id and name) ?

andydale · **Posted:** Fri Nov 17, 2006 11:20 am

Hi,

I hope i have understood your question correctly, you want to find an Attribute entity using the EntityManager.find(), is that correct ?

Assuming it is, you can only use EntityManager.find() if you know the primary key of the entity (Id in your case). You have stated that you only know the the Material_Id and the Name, you will probably have to use a query such as:

Code:

List result = em.createQuery("FROM Atrribute a WHERE a.name = :name").setParameter("name", "<name you know>")
                                .getResultList();

Cheers,

Andy

bhaal · **Posted:** Fri Nov 17, 2006 12:15 pm

Ok, you understood me, thank you.
Now I see that entity manager can't find beans based on data from more than one table, but only from one table primary key.

emmanuel · **Posted:** Thu Nov 23, 2006 1:13 pm

bhaal wrote:

Ok, you understood me, thank you.
Now I see that entity manager can't find beans based on data from more than one table, but only from one table primary key.

this is obviously wrong. HQL works at the object level, not the database level