[eclipselink-users] Meaning of FetchGroup#setShouldLoadAll(true)

[Frank Schwarz <fs5@xxxxxxx>]

Hi,

I've been investigating the new fetch-group feature(s) of EL 2.1.0 and there
is something I'd like to understand:

Lets say you have got "Employee" -- "Project" (many to many)

FetchGroup projectGroup = new FetchGroup();
projectGroup.addAttribute("name");

FetchGroup employeeGroup = new FetchGroup();
employeeGroup.addAttribute("id");
employeeGroup.addAttribute("name");
employeeGroup.addAttribute("projects", projectGroup);

TypedQuery<Employee> query = em.createQuery("select e from ...",
Employee.class);
query.setHint(QueryHints.FETCH_GROUP, employeeGroup);
query.setHint(QueryHints.BATCH, "e.projects");

List<Employee> emps = query.getResultList(); // (1)
for (Employee e : emps) {
  e.getProjekte().size(); // (2)
}

You can observe two sql statements. This first one at position (1) to load
all employees and the second one at position (2) to load all projects of all
previously loaded employees.

I would have expected the second sql statement to occur also at position
(1). I thought that this fetch plan was saying: Please ensure that all
employees and all their projects are loaded when you return from
"getResultList() and load all projects with a separate batch statement."

Would the following statement change the behavior to the one I am
expecting?:

employeeGroup.setShouldLoadAll(true);

And, is batch fetching compatible with this setting?


Thank you for your help,
Frank


PS: It is currently not possible to simply test it, as it will raise a NPE
at
org.eclipse.persistence.internal.sessions.AbstractSession$1.iterate(AbstractSession.java:4067)

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