Expected behavior for relations when putting entity

[vadimh77]

Hi,

I have the next structure:

@Entity
class CalEventEntity constructor(){
@Id(assignable = true)
    var id: Long = 0
    lateinit var recurrence: ToOne<CalEventRecurrenceEntity>
}

@Entity
data class CalEventRecurrenceEntity(@Id var id: Long=0,
                                    var anchorUid: String?,
                                    var originalStart: Long//,
                                    /*var endsAt : Long*/)
{
    @Backlink
    lateinit var rules: ToMany<RecurrenceRuleEntity>

}

@Entity
data class RecurrenceRuleEntity(@Id var id: Long=0,
                                var rule : String) {

    lateinit var eventRecurrence: ToOne<CalEventRecurrenceEntity>
}

Full logic Description:

1. I am getting from server the CalEventEntity with predefined id and then i am attaching it to the box: DBManager.eventDAO.box().attach(eventEntity)

2. I am creating a new instance :
   val calEventRecurrenceEntity = CalEventRecurrenceEntity(0,null,0) //notice the id is 0 as required

3. Then i am creating a new instance:
   val ruleEntity = RecurrenceRuleEntity(0, rule)

4. adding the rule: calEventRecurrenceEntity.rules.add(ruleEntity)

5. Adding the recurrence object to the calEvent:
   eventEntity.recurrence.target = calEventRecurrenceEntity

The problem is that the rules are not saved in the DB, i think that the problem is the the CalEventEntity has already ID.
Anyway, i expect the code to update the calEventEntity and insert the CalEventRecurrenceEntity with it's relations to the DB.

full code

 val eventEntity = CalEventEntity(calEvent.id)
 DBManager.eventDAO.box().attach(eventEntity)


val calEventRecurrenceEntity = CalEventRecurrenceEntity(0,calEvent.recurrence.anchorRefId, calEvent.recurrence.originalStart)
                            if (calEvent.recurrence.rules != null) {
                                for (rule in calEvent.recurrence.rules) {
                                    val ruleEntity = RecurrenceRuleEntity(0, rule)

                                    calEventRecurrenceEntity.rules.add(ruleEntity)
                                }

                            }
                            eventEntity.recurrence.target = calEventRecurrenceEntity

Please help.

[greenrobot-team]

Do you actually put() calEventRecurrenceEntity at any point?

See also the relations documentation on One-To-Many relations.

There is also an example project using customers and orders.
-ut

[vadimh77]

I call put on the CalEventEntity only.
So i expect that it should put the relations too.

[vadimh77]

This is the complete code

val eventEntity = CalEventEntity(calEvent.id)
DBManager.eventDAO.box().attach(eventEntity)

val calEventRecurrenceEntity = CalEventRecurrenceEntity(0,calEvent.recurrence.anchorRefId, calEvent.recurrence.originalStart)
if (calEvent.recurrence.rules != null) {
    for (rule in calEvent.recurrence.rules) {
        val ruleEntity = RecurrenceRuleEntity(0, rule)
        calEventRecurrenceEntity.rules.add(ruleEntity)
     }
}

eventEntity.recurrence.target = calEventRecurrenceEntity
box.put(eventEntity)

[vadimh77]

If i need to put the "calEventRecurrenceEntity" first and then i need to put the eventEntity it makes me call the DB twice, it is not a good performance.

[greenrobot-team]

Alright, got it. Yes, this should work assuming:

• this is an Android project
• you are using the latest version (1.4.1).

Is that the case? Otherwise we will try to reproduce.
-ut

[vadimh77]

This is Android project.
Using Kotlin.

ObjectBox version 1.4.1.

Let me know if you need more info.

[greenrobot]

Do I understand correctly, that you have entities A, B, and C and:

• A has a to-one to B
• B has a to-many to C
• You are adding C objects to the to-many of B
• You call put on an A object only and expect objects of C to be persisted

Btw, ToMany lists have a applyChangesToDb method, you can call after modifing the to-many relation.

[vadimh77]

Your description of the scenario is correct, isn't it an expected behavior?

About your note:
applyChangesToDb persist entities, doing it for each entity it is a performance issue for me when iterating on many items.

[greenrobot]

Your description of the scenario is correct, isn't it an expected behavior?

Not really. Persistence of relations does not work with arbitrary depth/complexity, but primarily with direct connections. There may be cases in which this works (if the entiry chain is modified).

So the to do for us is that we must clarify and document the behavior. Also, we might dig into this to see if we could extend the current implementation if it makes sense.

So, thanks for rasing the topic.

About your note:
applyChangesToDb persist entities, doing it for each entity it is a performance issue for me when iterating on many items.

Yes, you should not do it per entity, but inside a transaction, typically with store.runInTx(...).

[vadimh77]

It still doesn't solve the problem, moreover, when you have long hierarchies of entities it becomes a big mess to handle it.

1. Tried to use calEventRecurrenceEntity.rules.applyChangesToDb()

Got the exception: The source entity was not yet persisted (no ID), use box.put() on it instead

2. Tried to do that: box().put(calEventRecurrenceEntity)

Got execption:
The source entity was not yet persisted (no ID), use box.put() on it instead

Any ideas how to solve it?

Tnx

[greenrobot]

OK, let's try to get the full picture here.

Got the exception: The source entity was not yet persisted (no ID), use box.put() on it instead

I assumed A and B were existing entities. Are A and B actually new, too?

[vadimh77]

A has id from server, but doesnt exist on local DB. It is id is not auto generated by object box.

B and C are new entites, their id is auto generated by the object box DB(i pass null as id in the constractor as need)

[vadimh77]

Just notice NONE of the A,B and C stored in DB. I always reinstall the app and test it from scratch.

[greenrobot]

A has id from server, but doesnt exist on local DB. It is id is not auto generated by object box.

This is important info. I just updated some docs on Object IDs. Especially check paragraphs "Object ID: new vs. persisted entities" and "Self-assigned Object IDs". Does that help?

[vadimh77]

As i understand:

In my case:
A has long id from server - attached to the box.
B doesn't have ID yet.
C doesn't have ID yet.

It sounds here that the only solution in this case it to:

1. Put A.
2. Put B.

The problem is that it has a limitation when using RX because the syntax looks like that:

.flatMapIterable { dcEvents -> dcEvents } //make the data iterable
.map { calEvent ->
//here comes the logic of creating the A,B and C.

}
map operator called per each entity, so i can't bind it with the transaction.
Currently, i collect the entities of type A and put it to the box in one call.

Do you have a solution for this situation?