JPA + EJB + JSF: how can design complicated query

Question

I am using netbean 6.8 btw.
Let say that I have 4 different tables: Company , Facility , Project , and Document . So the relationship is this. A company can have multiple facilities. A facility can have multiple projects, and a project can have multiple documents.

Company :
+companyNum: PK
+facilityNum: FK

Facility :
+facilityNum: PK
+projectNum: FK

Project :
+projectNum: PK
+drawingNum: FK

So when I create Entity Class From Database in netbean 6.8, I have 4 entity classes that named after the above 4 tables. So if I want to see all the Document in the database, then it is easy. In my SessionBean , I would do this:

@PersistenceContext
private EntityManager em;
List<Document> documents = em.createNamedQuery("Document.findAll").getResultList();

However, that is not all what I need. Let say that I want to know all the Document from a particular Company , or all the Document from a particular Project from a particular Facility from a particular Company . I am very new to JPA + EJB + JSF as a whole. Please help me out.

Answer 1

您的关系应使用@ManyToOne声明（例如，在“ projects集合中的Document ”中），然后在JPA查询中使用inner join @ManyToOne ，例如，为给定项目选择所有文档：

select d from Document d inner join d.projects p where p.id = ?

Answer 2

In my opinion, the Chapter 27 - The Java Persistence Query Language from The Java EE Tutorials is a decent introduction and will help you to get started with JPQL. This is actually where you should start.