code: /*
   * SPDX-License-Identifier: Apache-2.0
   * Copyright 2018-2020 The Feast Authors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     https://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package feast.serving.connectors;
  
  import feast.proto.serving.ServingAPIProto;
  import feast.proto.types.ValueProto;
  import java.util.List;
  import java.util.Map;
  
  public interface OnlineRetriever {
    /**
     * Get online features for the given entity rows using data retrieved from the Feature references
     * specified in FeatureTable request.
     *
     * <p>Each {@link Feature} optional in the returned list then corresponds to an {@link
     * ServingAPIProto.GetOnlineFeaturesRequestV2.EntityRow} provided by the user. If feature for a
     * given entity row is not found, will return an empty optional instead. The no. of {@link
     * Feature} returned should match the no. of given {@link
     * ServingAPIProto.GetOnlineFeaturesRequestV2.EntityRow}s
     *
     * @param entityRows list of entity rows to request features for.
     * @param featureReferences specifies the FeatureTable to retrieve data from
     * @param entityNames name of entities
     * @return list of {@link Feature}s corresponding to data retrieved for each entity row from
     *     FeatureTable specified in FeatureTable request.
     */
    List<List<Feature>> getOnlineFeatures(
        List<Map<String, ValueProto.Value>> entityRows,
        List<ServingAPIProto.FeatureReferenceV2> featureReferences,
        List<String> entityNames);
  }
  