*/
private S3QueryResultList<ActivityModel> getActivitysByAttachmentsType(UserModel userModel, String type, int num) {
Category category = new Category(type);
ActivityModelMeta meta = ActivityModelMeta.get();
ModelRefAttributeMeta<ActivityModel, ModelRef<UserModel>, UserModel> refMeta = meta.userModelRef;
CoreAttributeMeta<ActivityModel,Category> categoryMeta = meta.attachmentsType;
S3QueryResultList<ActivityModel> list = Datastore.query(meta)
.filter(refMeta.equal(userModel.getKey()), categoryMeta.equal(category))