Realm and auto increment Behavior (Android)

Question

I\'m trying to get data from Realm using an ID as a reference. However, when querying for an ID, I\'ve found that Realm is giving me the same ID for all elements (ID of 0).

Answer 1

Here is a genereic solution, personnaly I create a class named RealmUtils and I add this type of methods :

 public static int getPrimaryKey(Class c)
{
    Realm realm = Realm.getDefaultInstance();

    String primaryKeyFied = realm.getSchema().get(c.getSimpleName()).getPrimaryKey();
    if (realm.where(c).max(primaryKeyFied)== null)
        return 1;
    int value = realm.where(c).max(primaryKeyFied).intValue();
    return value+1;
}

Why I return 0 when the table is empty ? Because I hate Id's with 0 as value, so just change it. Hope it help someone.

Answer 2

As already mentioned, auto-increment isn't supported yet.

But for those who use kotlin and wants to have an auto-increment behavior with realm, this is one of the possibilities:

open class Route(
    @PrimaryKey open var id: Long? = null,
    open var total: Double? = null,
    open var durationText: String? = null,
    open var durationMinutes: Double? = null,
    open var distanceText: String? = null,
    open var distanceMeters: Int? = null): RealmObject() {

companion object {
    @Ignore var cachedNextId:Long? = null
        get() {
            val nextId =    if (field!=null) field?.plus(1)
                            else Realm.getDefaultInstance()?.where(Route::class.java)?.max("id")?.toLong()?.plus(1) ?: 1
            Route.cachedNextId = nextId
            return nextId
        }
}}

Answer 3

Realm currently doesn't support auto incrementing primary keys. However you can easily implement it yourself using something like:

public int getNextKey() { 
    try { 
         Number number = realm.where(object).max("id");
         if (number != null) {
             return number.intValue() + 1;
         } else {
             return 0;
         }
    } catch (ArrayIndexOutOfBoundsException e) { 
         return 0;
    }
}

I hope that can get you started.

Answer 4

//generates primary key
    public static int getNextKey(RealmQuery realmQuery, String fieldName) {
        try {
            Number number = realmQuery.max(fieldName);
            if (number != null) {
                return number.intValue() + 1;
            } else {
                return 1;
            }
        } catch (ArrayIndexOutOfBoundsException e) {
            return 1;
        }
    }

Example

int id = RealmDbHelper.getNextKey(realm.where(RealmDocument.class), RealmDocument.FIELD_DOCUMENT_ID)
    realmObject.setId(id);
    realm.insert(realmObject);

Answer 5

if your Id is Long then:

val nextId = bgRealm.where(Branch::class.java).max("localId") as Long + 1

Answer 6

The Java binding does not support primary keys yet, but it's on the roadmap and with high priority - see: https://groups.google.com/forum/#!topic/realm-java/6hFqdyoH67w . As a workaround you can use this piece of code for generating keys:

int key;
try {
  key = realm.where(Child_pages.class).max("id").intValue() + 1;
} catch(ArrayIndexOutOfBoundsException ex) {
 key = 0;
}

I use singleton factory for generating primary keys as a more generic solution with better performance (no need to query for max("id") every time thanks to AtomicInteger).

There is a long discussion in Realm Git Hub if you need more context: Document how to set an auto increment id?