EJB3.0 persistence API

[Jack Lau]

Hello,

I have a question about using EJB3.0 persistence API. If I write a query which join some tables e.g 3 tables (a, b, c), so there are number of fields (a.f1, b.f1, c.f2) retrieved. I am using query.getResultList() to return a Vector, but I want the result is an object collection so that I can use it to call it's method to retrieve the value of field, does anyone how to do this?

Thanks,
Jack

[Bill Shirley]

Originally posted by Jack Lau:
Hello,

I have a question about using EJB3.0 persistence API. If I write a query which join some tables e.g 3 tables (a, b, c), so there are number of fields (a.f1, b.f1, c.f2) retrieved. I am using query.getResultList() to return a Vector, but I want the result is an object collection so that I can use it to call it's method to retrieve the value of field, does anyone how to do this?

Thanks,
Jack

getResultList() return a (non-generified java.util) List.
List is a collection.

It is highly suggested (and all java.util Collections do), that Collections should have a constructor that takes a collection (and adds its elements into the new collection).

If you want the 5.0 generified version of some collection:
new LinkedList<MyTypes>(resultList);
will do it,

[Mike Keith]

Jack,

The result of getResultList() is a List. If you simply returned a single type of entity from the query then you would be able to do the following:

Query q = em.createQuery("SELECT e FROM Employee e WHERE e.sal > 50000");
List<Employee> emps = (List<Employee> :wink: (q.getResultList());

If you have a SELECT clause containing multiple items then each element of the List will be an array of Object (Object[]) that contains all of the select items. Unfortunately this is an array, not a Collection, and you can't narrow it, even if the objects stored in it were the same type (which is not very likely anyway).

[Jack Lau]

Thanks!

But if I want to return more than 1 entity, I found that there is an anontation called @SqlResultSetMapping but I do not know how to use it...

    
-- sql = "select e.name as emp_name, m.name as manager_name from emp e,    
-- emp m where ...."
@SqlResultSetMapping(
    name="EmployeeAndManager",
    columns={@ColumnResult(name="EMP_NAME"),
             @ColumnResult(name="MANAGER_NAME")}
)

How to get the result and what is the return type of the @SqlResultSetMapping ?

Thanks,
Jack

[Mike Keith]

I wouldn't recommend using raw SQL queries and @SqlResultSetMapping annotations. The result will be the same as if you used JPQL, except that they will be more work to map the result and less portable.