realm link queries with conjunction

Question

Almost same question than Realm, complex linked query, but with a important variant :

In the official docs, https://realm.io/docs/java/latest/#link-queries - there's an example how to select owners of "Brown" dogs and owner of "Fluffy" dogs. Not, as written in former question, "Brown Fluffy" dogs, because the code examples do not realize a conjunction.

So my question is: how to get only persons who own a "Brown" and "Fluffy" dog (both conditions on the same dog)? That is only U2, given the data of the example. The second code example from the docs adds a third filter "Yellow", so the answer seems right, but there is still not a conjunction on the fields of the same Dog. Below are my attempts from the docs:

// returns both U1 and U2, because U1 owns a Brown dog, and U2 a Fluffy
RealmResults<Person> r1 = realm.where(Person.class)
            .equalTo("dogs.name", "Fluffy")
            .equalTo("dogs.color", "Brown")
            .findAll();
// returns both U1 and U2, because U1 has a Fluffy but it is red, and has also a brown dog (Fido)
RealmResults<Person> r2 = realm.where(Person.class)
            .equalTo("dogs.name", "Fluffy")
            .findAll()
            .where()
            .equalTo("dogs.color", "Brown")
            .findAll();

I would need to check a conjunction of conditions over subelements in array. I need to realize it as a Query, to fill an adapter. It is possible with Realm?

I was dreaming of a new kind of grouping for conditions which allow to specify several conditions on items of a List field, like this:

RealmResults<Person> r3 = realm.where(Person.class)
    .beginFilterAny("dogs") // keep only Persons whose at least one dog satisfy:
        .equalTo("name", "Fluffy")
        .equalTo("color", "Brown")
    .endFilterAny()
    .findAll();

score 0 · Answer 1 · answered Dec 14 '18 at 21:24

0

You can define an inverse relationship and query for the dog by name and color. You can then iterate over the dogs and get the owners.

answered Dec 14 '18 at 21:24

geisshirt

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The point is not to get the owners, but to build automatically a managed collection for a RealmRecyclerViewAdapter. If I build a RealmList by a iteration of the dogs, it won't be managed. But I may be able to use [link](https://stackoverflow.com/a/40632613/5585820) to filter the results. – Pierre N. Dec 16 '18 at 08:42

score 0 · Answer 2 · answered Jan 08 '19 at 12:20

Use a query on Dog.class with those conditions, so you'll have all Brown and Fluffy dogs. Iterate the result to extract all dogs primary key and use it in a query on Person.class to retrieve all persons owning at least one of those dogs.

//get all brown and fluffy dogs
RealmResults<Dog> dogs = realm.where(Dog.class)
     .equalTo("name", "Fluffy")
     .equalTo("color", "Brown")
     .findAll();

//extract dogs id
Set<UUID> dogIds = dogs.stream()
    .map(d -> d.getId().toString())
    .collect(Collectors.toSet());

//find all brown and fluffy dogs owners
RealmResults<Person> persons = realm.where(Person.class)
     .in("dogs.id", dogIds.toArray(new String[dogIds.size()]))
     .findAll();

realm link queries with conjunction

2 Answers2