use & save syncExpression (MVP)

1. use serializedSyncExpression in lookupLastSyncTime
2. save serializedSyncExpression along with lastSyncTime

Author: Edison Zhang

aws-datastore/src/main/java/com/amplifyframework/datastore/syncengine/SyncProcessor.java

@@ -46,7 +46,9 @@
 import com.amplifyframework.hub.HubChannel;
 import com.amplifyframework.hub.HubEvent;
 import com.amplifyframework.logging.Logger;
+import com.amplifyframework.util.GsonFactory;
 import com.amplifyframework.util.Time;
+import com.google.gson.Gson;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -80,6 +82,7 @@ final class SyncProcessor {
     private final DataStoreConfigurationProvider dataStoreConfigurationProvider;
     private final QueryPredicateProvider queryPredicateProvider;
     private final RetryHandler requestRetry;
+    private final Gson gson;    //TODO: for pre-deserialization of QueryPredicate, will remove shortly
 
     /**
      * The `isSyncRetryEnabled` value is being passed down all the way from the `AWSDataStorePlugin` or the
@@ -97,7 +100,7 @@ private SyncProcessor(Builder builder) {
         this.queryPredicateProvider = builder.queryPredicateProvider;
         this.requestRetry = builder.requestRetry;
         this.isSyncRetryEnabled = builder.isSyncRetryEnabled;
-
+        this.gson = GsonFactory.instance();     //TODO: for pre-deserialization of QueryPredicate, will remove shortly
         if (!this.isSyncRetryEnabled) {
             LOG.warn("Disabling sync retries will be deprecated in a future version.");
         }
@@ -182,10 +185,9 @@ Completable hydrate() {
 
     private Completable createHydrationTask(ModelSchema schema) {
         ModelSyncMetricsAccumulator metricsAccumulator = new ModelSyncMetricsAccumulator(schema.getName());
-        //TODO: QueryPredicate currentPredicate = this.queryPredicateProvider.getPredicate(schema.getName());
-        //TODO deserialize current predicate to deserializedCurrentPredicate
-        //TODO: pass deserializedCurrentPredicate to lookupLastSyncTime as the second parameter
-        return syncTimeRegistry.lookupLastSyncTime(schema.getName())
+        QueryPredicate currentPredicate = this.queryPredicateProvider.getPredicate(schema.getName());
+        String serializedSyncExpression = gson.toJson(currentPredicate); //TODO: for pre-deserialization of QueryPredicate, will remove shortly
+        return syncTimeRegistry.lookupLastSyncTime(schema.getName(), serializedSyncExpression)
             .map(this::filterOutOldSyncTimes)
             // And for each, perform a sync. The network response will contain an Iterable<ModelWithMetadata<T>>
             .flatMap(lastSyncTime -> {
@@ -204,10 +206,9 @@ private Completable createHydrationTask(ModelSchema schema) {
                     .toSingle(() -> lastSyncTime.exists() ? SyncType.DELTA : SyncType.BASE);
             })
             .flatMapCompletable(syncType -> {
-                //TODO: pass the deserializedCurrentPredicate to saveLastDelta/BaseSync as the third parameter
                 Completable syncTimeSaveCompletable = SyncType.DELTA.equals(syncType) ?
-                    syncTimeRegistry.saveLastDeltaSyncTime(schema.getName(), SyncTime.now(), null) :
-                    syncTimeRegistry.saveLastBaseSyncTime(schema.getName(), SyncTime.now(), null);
+                    syncTimeRegistry.saveLastDeltaSync(schema.getName(), SyncTime.now(), serializedSyncExpression) :
+                    syncTimeRegistry.saveLastBaseSync(schema.getName(), SyncTime.now(), serializedSyncExpression);
                 return syncTimeSaveCompletable.andThen(Completable.fromAction(() ->
                     Amplify.Hub.publish(
                         HubChannel.DATASTORE, metricsAccumulator.toModelSyncedEvent(syncType).toHubEvent()

aws-datastore/src/main/java/com/amplifyframework/datastore/syncengine/SyncTimeRegistry.java

@@ -17,6 +17,7 @@
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.core.util.ObjectsCompat;
 
 import com.amplifyframework.core.model.query.Where;
 import com.amplifyframework.core.model.query.predicate.QueryField;
@@ -40,27 +41,27 @@ final class SyncTimeRegistry {
         this.localStorageAdapter = localStorageAdapter;
     }
 
-    //TODO: add the second argument: current sync expression here
-    Single<SyncTime> lookupLastSyncTime(@NonNull String modelClassName) {
+    Single<SyncTime> lookupLastSyncTime(@NonNull String modelClassName, @NonNull String syncExpression) {
         return Single.create(emitter -> {
             QueryPredicate hasMatchingModelClassName = QueryField.field("modelClassName").eq(modelClassName);
 
             localStorageAdapter.query(LastSyncMetadata.class, Where.matches(hasMatchingModelClassName), results -> {
                 try {
                     LastSyncMetadata syncMetadata = extractSingleResult(modelClassName, results);
-                    //TODO: syncMetadata should contain the previous serialized sync expression
-                    //TODO: compare the previous sync expression with the current one
-                    //TODO: emmit SyncTime.never() if different
-                    emitter.onSuccess(SyncTime.from(syncMetadata.getLastSyncTime()));
+                    SyncTime lastSyncTime = SyncTime.from(syncMetadata.getLastSyncTime());
+                    String lastSyncExpression = syncMetadata.getSyncExpression();
+                    if(!ObjectsCompat.equals(lastSyncExpression, syncExpression)){
+                        lastSyncTime = SyncTime.never();
+                    }
+                    emitter.onSuccess(lastSyncTime);
                 } catch (DataStoreException queryResultFailure) {
                     emitter.onError(queryResultFailure);
                 }
             }, emitter::onError);
         });
     }
 
-    //TODO: change the name to saveLastDeltaSync, and add the second argument for sync expression
-    Completable saveLastDeltaSyncTime(@NonNull String modelClassName, @Nullable SyncTime syncTime, @Nullable String syncExpression) {
+    Completable saveLastDeltaSync(@NonNull String modelClassName, @Nullable SyncTime syncTime, @Nullable String syncExpression) {
         LastSyncMetadata metadata = syncTime != null && syncTime.exists() ?
             LastSyncMetadata.deltaSyncedAt(modelClassName, syncTime.toLong(), syncExpression) :
             LastSyncMetadata.neverSynced(modelClassName);
@@ -76,8 +77,7 @@ Completable saveLastDeltaSyncTime(@NonNull String modelClassName, @Nullable Sync
         );
     }
 
-    //TODO: change the name to saveLastDeltaSync, and add the second argument for sync expression
-    Completable saveLastBaseSyncTime(@NonNull String modelClassName, @Nullable SyncTime syncTime, @Nullable String syncExpression) {
+    Completable saveLastBaseSync(@NonNull String modelClassName, @Nullable SyncTime syncTime, @Nullable String syncExpression) {
         LastSyncMetadata metadata = syncTime != null && syncTime.exists() ?
             LastSyncMetadata.baseSyncedAt(modelClassName, syncTime.toLong(), syncExpression) :
             LastSyncMetadata.neverSynced(modelClassName);