JdbcTableReadContextLoader.java

/**
 * Copyright 2017 StreamSets Inc.
 *
 * Licensed under 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 com.streamsets.pipeline.stage.origin.jdbc.table.cache;

import com.google.common.cache.CacheLoader;
import com.streamsets.pipeline.stage.origin.jdbc.table.ConnectionManager;
import com.streamsets.pipeline.stage.origin.jdbc.table.TableContext;
import com.streamsets.pipeline.stage.origin.jdbc.table.TableJdbcELEvalContext;
import com.streamsets.pipeline.stage.origin.jdbc.table.TableReadContext;
import com.streamsets.pipeline.stage.origin.jdbc.table.util.OffsetQueryUtil;
import org.apache.commons.lang3.tuple.Pair;

import java.util.List;
import java.util.Map;

/**
 * Loads a {@link TableReadContext} for corresponding {@link TableContext}
 * Users can then use {@link TableReadContext#getResultSet()} to read rows
 * from the corresponding table
 */
public class JdbcTableReadContextLoader extends CacheLoader<TableContext, TableReadContext>{
  private final ConnectionManager connectionManager;
  private final TableJdbcELEvalContext tableJdbcELEvalContext;
  private final Map<String, String> offsets;
  private final int fetchSize;
  private final String quoteChar;

  public JdbcTableReadContextLoader(
      ConnectionManager connectionManager,
      Map<String, String> offsets,
      int fetchSize,
      String quoteChar,
      TableJdbcELEvalContext tableJdbcELEvalContext
  ) {
    this.connectionManager = connectionManager;
    this.offsets = offsets;
    this.fetchSize = fetchSize;
    this.quoteChar = quoteChar;
    this.tableJdbcELEvalContext = tableJdbcELEvalContext;
  }

  @Override
  public TableReadContext load(TableContext tableContext) throws Exception {
    Pair<String, List<Pair<Integer, String>>> queryAndParamValToSet =
        OffsetQueryUtil.buildAndReturnQueryAndParamValToSet(
            tableContext,
            offsets.get(tableContext.getQualifiedName()),
            quoteChar,
            tableJdbcELEvalContext
        );

    TableReadContext tableReadContext =
        new TableReadContext(
            connectionManager.getConnection(),
            queryAndParamValToSet.getLeft(),
            queryAndParamValToSet.getRight(),
            fetchSize
        );

    //Clear the initial offset after the  query is build so we will not use the initial offset from the next
    //time the table is used.
    tableContext.clearStartOffset();

    return tableReadContext;
  }
}