Return true if update() data changed

src/main/java/it/cavallium/dbengine/database/LLDictionary.java

@@ -17,7 +17,7 @@ public interface LLDictionary extends LLKeyValueDatabaseStructure {
 
 	Mono<byte[]> put(byte[] key, byte[] value, LLDictionaryResultType resultType);
 
-	Mono<Void> update(byte[] key, Function<Optional<byte[]>, Optional<byte[]>> updater);
+	Mono<Boolean> update(byte[] key, Function<Optional<byte[]>, Optional<byte[]>> updater);
 
 	Mono<byte[]> remove(byte[] key, LLDictionaryResultType resultType);
 

src/main/java/it/cavallium/dbengine/database/collections/DatabaseMapDictionary.java

@@ -11,6 +11,7 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Optional;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
 import org.jetbrains.annotations.Nullable;
 import reactor.core.publisher.Flux;
@@ -109,12 +110,11 @@ public class DatabaseMapDictionary<T, U> extends DatabaseMapDictionaryDeep<T, U,
 	}
 
 	@Override
-	public Mono<Void> updateValue(T keySuffix, Function<Optional<U>, Optional<U>> updater) {
+	public Mono<Boolean> updateValue(T keySuffix, Function<Optional<U>, Optional<U>> updater) {
-		return dictionary
+		AtomicBoolean changed = new AtomicBoolean(false);
-				.update(toKey(serializeSuffix(keySuffix)),
+		return dictionary.update(toKey(serializeSuffix(keySuffix)),
 				oldSerialized -> updater.apply(oldSerialized.map(this::deserialize)).map(this::serialize)
-				)
+		);
-				.then();
 	}
 
 	@Override

src/main/java/it/cavallium/dbengine/database/collections/DatabaseSingle.java

@@ -42,7 +42,7 @@ public class DatabaseSingle<U> implements DatabaseStageEntry<U> {
 	}
 
 	@Override
-	public Mono<Void> update(Function<Optional<U>, Optional<U>> updater) {
+	public Mono<Boolean> update(Function<Optional<U>, Optional<U>> updater) {
 		return dictionary.update(key,
 				(oldValueSer) -> updater.apply(oldValueSer.map(this::deserialize)).map(this::serialize)
 		);

src/main/java/it/cavallium/dbengine/database/collections/DatabaseSingleMapped.java

@@ -43,7 +43,7 @@ public class DatabaseSingleMapped<U> implements DatabaseStageEntry<U> {
 	}
 
 	@Override
-	public Mono<Void> update(Function<Optional<U>, Optional<U>> updater) {
+	public Mono<Boolean> update(Function<Optional<U>, Optional<U>> updater) {
 		return serializedSingle.update(oldValue -> updater.apply(oldValue.map(this::deserialize)).map(this::serialize));
 	}
 

src/main/java/it/cavallium/dbengine/database/collections/DatabaseStage.java

@@ -25,7 +25,7 @@ public interface DatabaseStage<T> extends DatabaseStageWithEntry<T> {
 		return setAndGetPrevious(value).map(oldValue -> !Objects.equals(oldValue, value)).defaultIfEmpty(false);
 	}
 
-	Mono<Void> update(Function<Optional<T>, Optional<T>> updater);
+	Mono<Boolean> update(Function<Optional<T>, Optional<T>> updater);
 
 	default Mono<Void> clear() {
 		return clearAndGetStatus().then();

src/main/java/it/cavallium/dbengine/database/collections/DatabaseStageMap.java

@@ -29,7 +29,7 @@ public interface DatabaseStageMap<T, U, US extends DatabaseStage<U>> extends Dat
 		return at(null, key).single().flatMap(v -> v.set(value));
 	}
 
-	default Mono<Void> updateValue(T key, Function<Optional<U>, Optional<U>> updater) {
+	default Mono<Boolean> updateValue(T key, Function<Optional<U>, Optional<U>> updater) {
 		return at(null, key).single().flatMap(v -> v.update(updater));
 	}
 
@@ -110,7 +110,7 @@ public interface DatabaseStageMap<T, U, US extends DatabaseStage<U>> extends Dat
 	}
 
 	@Override
-	default Mono<Void> update(Function<Optional<Map<T, U>>, Optional<Map<T, U>>> updater) {
+	default Mono<Boolean> update(Function<Optional<Map<T, U>>, Optional<Map<T, U>>> updater) {
 		return this
 				.getAllValues(null)
 				.collectMap(Entry::getKey, Entry::getValue, HashMap::new)
@@ -119,7 +119,9 @@ public interface DatabaseStageMap<T, U, US extends DatabaseStage<U>> extends Dat
 				.map(updater)
 				.filter(Optional::isPresent)
 				.map(Optional::get)
-				.flatMap(values -> this.setAllValues(Flux.fromIterable(values.entrySet())));
+				.flatMap(values -> this.setAllValues(Flux.fromIterable(values.entrySet())))
+				//todo: can be optimized by calculating the correct return value
+				.thenReturn(true);
 	}
 
 	@Override

src/main/java/it/cavallium/dbengine/database/disk/LLLocalDictionary.java

@@ -220,9 +220,9 @@ public class LLLocalDictionary implements LLDictionary {
 	}
 
 	@Override
-	public Mono<Void> update(byte[] key, Function<Optional<byte[]>, Optional<byte[]>> value) {
+	public Mono<Boolean> update(byte[] key, Function<Optional<byte[]>, Optional<byte[]>> value) {
 		return Mono
-						.<Void>fromCallable(() -> {
+						.fromCallable(() -> {
 							var rwuLock = itemsLock.getAt(getLockIndex(key));
 							rwuLock.updateLock().lock();
 							try {
@@ -238,10 +238,12 @@ public class LLLocalDictionary implements LLDictionary {
 									prevData = Optional.empty();
 								}
 
+								boolean changed = false;
 								Optional<byte[]> newData = value.apply(prevData);
 								if (prevData.isPresent() && newData.isEmpty()) {
 									rwuLock.writeLock().lock();
 									try {
+										changed = true;
 										db.delete(cfh, key);
 									} finally {
 										rwuLock.writeLock().unlock();
@@ -250,12 +252,13 @@ public class LLLocalDictionary implements LLDictionary {
 										&& (prevData.isEmpty() || !Arrays.equals(prevData.get(), newData.get()))) {
 									rwuLock.writeLock().lock();
 									try {
+										changed = true;
 										db.put(cfh, key, newData.get());
 									} finally {
 										rwuLock.writeLock().unlock();
 									}
 								}
-								return null;
+								return changed;
 							} finally {
 								rwuLock.updateLock().unlock();
 							}