How to get parent object in Realm

Question

Reference to realms doc

I have some entities, for example it is: Category and Item.
The Category contains RealmList of Items and I can access all items of category by calling getter of this list.
But how can I query all items by category's id(it's annotated as primary key)
I'm parsing json via Realm.createObjectFromJson() and can't set Category field to each Item
Thanx in advance

Realm JS Issue for this: https://github.com/realm/realm-js/issues/343 — Joshua Pinter, Jun 22 '16 at 21:07

score 6 · Accepted Answer · answered Aug 13 '15 at 18:29

6

If there isn't any link from your Item to your Category you cannot currently query Items based on the Category. The concept you are looking for is on our TODO and is called backlinks. You can follow progress on that here: https://github.com/realm/realm-java/issues/607

The current workaround would be to manually create that link after you copied them to Realm:

realm.beginTransaction();
Category category = realm.createObjectFromJson(categoryJson);
for (Item item : category.getItems()) {
  item.setCategory(category);
}
realm.commitTransaction();

// Then you can do
realm.where(Item.class).equalTo("category.id", category.getId()).findAll();

answered Aug 13 '15 at 18:29

Christian Melchior

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or at least automatically set the category field for each of Category's Items (if that field exists in Item class) while parsing – uneven Aug 14 '15 at 03:40
Yes, that is actually idea behind backlinks, that they will be set automatically. – Christian Melchior Aug 14 '15 at 09:14
I thought "category.id" was the fieldname how is there a period in the field name? – Ed Lee Dec 08 '16 at 19:42
Backlinks are already available. https://proandroiddev.com/realm-backlinks-queries-to-linking-objects-and-changes-in-schema-design-d64de74f1608 – Roman Nazarevych Nov 30 '18 at 17:55

How to get parent object in Realm

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