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RealmAutoIncrement is a singleton which maintain the last id saved from each database model
package com.carlosedurdo.database;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;
import io.realm.Realm;
import io.realm.RealmObject;
* Implementation of Auto Increment feature for Realm
* RealmAutoIncrement is a singleton which maintain the last id saved from each database model.
* To get next id from anyone model, simple call the method getNextIdFromModel.
* @see #getNextIdFromModel(Class)
public final class RealmAutoIncrement {
private Realm realm;
private Map<Class<? extends RealmObject>, AtomicInteger> modelMap = new HashMap<>();
private static RealmAutoIncrement autoIncrementMap;
private RealmAutoIncrement() {
realm = Realm.getDefaultInstance();
modelMap.put(SampleModel.class, new AtomicInteger(getLastIdFromModel(SampleModel.class)));
* Utility method which query for all models saved and get the bigger model id saved
* Used to guarantee which the last model id saved is really the last
* @param clazz Model which should get the last id
* @return The last id saved from model passed
private int getLastIdFromModel(Class<? extends RealmObject> clazz) {
String primaryKeyColumnName = "id";
Number lastId = realm.where(clazz).max(primaryKeyColumnName);
return lastId == null ? 0 : lastId.intValue();
* Search in modelMap for the last saved id from model passed and return the next one
* @param clazz Model to search the last id
* @return The next id which can be saved in database for that model,
* {@code null} will be returned when this method is called by reflection
public Integer getNextIdFromModel(Class<? extends RealmObject> clazz) {
if (isValidMethodCall()) {
AtomicInteger modelId = modelMap.get(clazz);
if (modelId == null) {
return 0;
return modelId.incrementAndGet();
return null;
* Utility method to validate if the method is called from reflection,
* in this case is considered a not valid call otherwise is a valid call
* @return The boolean which define if the method call is valid or not
private boolean isValidMethodCall() {
StackTraceElement[] stackTraceElements = Thread.currentThread().getStackTrace();
for (StackTraceElement stackTraceElement : stackTraceElements) {
if (stackTraceElement.getMethodName().equals("newInstance")) {
return false;
return true;
public static RealmAutoIncrement getInstance() {
if (autoIncrementMap == null) {
autoIncrementMap = new RealmAutoIncrement();
return autoIncrementMap;
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