Support data observers for related entities

[jpmcosta]

Note these related feature requests:

• Support observing individual objects #126
• Support data observers for related entities #268

---

This might be a feature request.
It seems that currently it is not possible to listen for nested changes.

• ObjectBox version: 1.2.1
• Reproducibility: always

boxFor(Item::class.java).query().build().subscribe().observer { items ->
    // Not called when Note.text changes.
}

Entities

@Entity
class Item {

    @Id
    open var id: Long = 0L

    lateinit open var notes: ToMany<Note>
}

@Entity
class Note {

    @Id
    open var id: Long = 0L

    open var text: String? = null

    @Backlink
    lateinit open var parentItem: ToOne<Item>
}

[jpmcosta]

I think the following code could also trigger changes in data observers:

item.notes.add(Note())
item.notes.applyChangesToDb()

[greenrobot]

I thought we have tracked that already, but did not find it...

[mecoFarid]

applyChangesToDb

It will throw an exception if you try to call it on untracked changes. Like if it's first time you're putting that Note into box

[mecoFarid]

I thought we have tracked that already, but did not find it...

Seems like abondened issue

[greenrobot-team]

@mecoFarid If you are interested in this feature, please thumbs up the first post!

[mecoFarid]

@greenrobot-team Could be an unrelated place to ask but is there any workaround other than applyChangesToDb() which throws exception for untracted changes?

[greenrobot-team]

@mecoFarid Not sure what you mean, calling applyChangesToDb() is not a workaround for the reported issue AFAIK.

A workaround to not getting notifications on related entities is to observe the box of the related entity as well. Using the above example:

boxFor(Note::class.java).query().build().subscribe().observer { items ->
    // Called when Note.text changes.
}

[greenrobot-team]

Please vote for #59

[greenrobot-team]

Hm, actually might want to keep this separate. Reopening.