sdks/java/io/cassandra/src/main/java/org/apache/beam/sdk/io/cassandra/ReadFn.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 *
 *     http://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 org.apache.beam.sdk.io.cassandra;

import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.ColumnMetadata;
import com.datastax.driver.core.PreparedStatement;
import com.datastax.driver.core.ResultSet;
import com.datastax.driver.core.Session;
import com.datastax.driver.core.Token;
import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import java.util.stream.Collectors;
import org.apache.beam.sdk.io.cassandra.CassandraIO.Read;
import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Joiner;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@SuppressWarnings({
  "rawtypes", // TODO(https://issues.apache.org/jira/browse/BEAM-10556)
  "nullness" // TODO(https://issues.apache.org/jira/browse/BEAM-10402)
})
class ReadFn<T> extends DoFn<Read<T>, T> {

  private static final Logger LOG = LoggerFactory.getLogger(ReadFn.class);

  @ProcessElement
  public void processElement(@Element Read<T> read, OutputReceiver<T> receiver) {
    try {
      Session session = ConnectionManager.getSession(read);
      Mapper<T> mapper = read.mapperFactoryFn().apply(session);
      String partitionKey =
          session.getCluster().getMetadata().getKeyspace(read.keyspace().get())
              .getTable(read.table().get()).getPartitionKey().stream()
              .map(ColumnMetadata::getName)
              .collect(Collectors.joining(","));

      String query = generateRangeQuery(read, partitionKey, read.ringRanges() != null);
      PreparedStatement preparedStatement = session.prepare(query);
      Set<RingRange> ringRanges =
          read.ringRanges() == null ? Collections.emptySet() : read.ringRanges().get();

      for (RingRange rr : ringRanges) {
        Token startToken = session.getCluster().getMetadata().newToken(rr.getStart().toString());
        Token endToken = session.getCluster().getMetadata().newToken(rr.getEnd().toString());
        ResultSet rs =
            session.execute(preparedStatement.bind().setToken(0, startToken).setToken(1, endToken));
        Iterator<T> iter = mapper.map(rs);
        while (iter.hasNext()) {
          T n = iter.next();
          receiver.output(n);
        }
      }

      if (read.ringRanges() == null) {
        ResultSet rs = session.execute(preparedStatement.bind());
        Iterator<T> iter = mapper.map(rs);
        while (iter.hasNext()) {
          receiver.output(iter.next());
        }
      }
    } catch (Exception ex) {
      LOG.error("error", ex);
    }
  }

  private Session getSession(Read<T> read) {
    Cluster cluster =
        CassandraIO.getCluster(
            read.hosts(),
            read.port(),
            read.username(),
            read.password(),
            read.localDc(),
            read.consistencyLevel(),
            read.connectTimeout(),
            read.readTimeout());

    return cluster.connect(read.keyspace().get());
  }

  private static String generateRangeQuery(
      Read<?> spec, String partitionKey, Boolean hasRingRange) {
    final String rangeFilter =
        (hasRingRange)
            ? Joiner.on(" AND ")
                .skipNulls()
                .join(
                    String.format("(token(%s) >= ?)", partitionKey),
                    String.format("(token(%s) < ?)", partitionKey))
            : "";
    final String combinedQuery = buildInitialQuery(spec, hasRingRange) + rangeFilter;
    LOG.debug("CassandraIO generated query : {}", combinedQuery);
    return combinedQuery;
  }

  private static String buildInitialQuery(Read<?> spec, Boolean hasRingRange) {
    return (spec.query() == null)
        ? String.format("SELECT * FROM %s.%s", spec.keyspace().get(), spec.table().get())
            + " WHERE "
        : spec.query().get() + (hasRingRange ? " AND " : "");
  }
}