Question

I’m trying to create an object and populate members of a foreign collection held by that object in a single operation. I’ve tried every ordering of operations I can think of, and just can’t seem to get it to work.

My classes are (skipping irrelevant fields and annotations):

@DatabaseTable
public class ScheduledJob
{
    @DatabaseField(id=true)
    private String id = UUID.randomUUID ().toString ();

    @ForeignCollectionField(eager=true)
    private Collection<ScheduledJobTask> tasks;

    /* other stuff here ... */
}

@DatabaseTable
public class ScheduledJobTask
{
    @DatabaseField(id=true)
    private String id = UUID.randomUUID ().toString ();
    @DatabaseField(foreign=true)
    private ScheduledJob job;
    /* more other stuff ... */

    public ScheduledJobTask(Task t) { 
       /* initialise scheduled task from template task by copying relevant fields...*/ 
    }

}

I create my objects thus:

ScheduledJob job = new ScheduledJob ();
// fill in other fields of job here
job.tasks = new ArrayList<ScheduledJobTask> ();
for (Task t : template.getTasks())
    job.tasks.add(new ScheduledJobTask(t));

sched.getSchedule().add (job);  // 'sched' is an object loaded from another table, this
                                // adds 'job' to a foreign collection in that table
Storage.store.scheduledJobs.createIfNotExists (job);
for (ScheduledJobTask t : job.getTasks ())
    Storage.store.scheduledJobTasks.createIfNotExists (t);
Storage.store.daySchedules.update (sched);

I have tried all orderings of the last three statements, but nothing seems to work: in every case, the entries that end up in the scheduledjobtask database table have null for their ‘job_id’ field.

Any ideas what I’ve done wrong?

Answer 1

What you are missing is that you are not setting the Task.job field. The ScheduledJobTask.job field is what sets up the foreign collection. When you retrieve a Job, it looks in the task table to find all of the tasks that have that job — not the other way around.

You will need to do something like:

for (Task t : template.getTasks()) {
    t.setJob(job);
    job.tasks.add(new ScheduledJobTask(t));
}

Then, when you do this:

Storage.store.scheduledJobs.createIfNotExists (job);

all of the job fields will have a Job that has an id field set. So when you persist your tasks, their job fields will have that job id.