code: public List<Key> multiplePutEntitiesDeferredId() {
      Datastore datastore = transaction.getDatastore();
      // [START multiplePutEntitiesDeferredId]
      IncompleteKey key1 = datastore.newKeyFactory().setKind("MyKind").newKey();
      FullEntity.Builder entityBuilder1 = FullEntity.newBuilder(key1);
      entityBuilder1.set("propertyName", "value1");
      FullEntity entity1 = entityBuilder1.build();
  
      IncompleteKey key2 = datastore.newKeyFactory().setKind("MyKind").newKey();
      FullEntity.Builder entityBuilder2 = FullEntity.newBuilder(key2);
      entityBuilder2.set("propertyName", "value2");
      FullEntity entity2 = entityBuilder2.build();
  
      transaction.putWithDeferredIdAllocation(entity1, entity2);
      Response response = transaction.commit();
      // [END multiplePutEntitiesDeferredId]
      return response.getGeneratedKeys();
    }
docs: [TARGET putWithDeferredIdAllocation(FullEntity...)]