edu.yale.cs.hadoopdb.connector
Class DBRecordReader<T extends DBWritable>

java.lang.Object
  edu.yale.cs.hadoopdb.connector.AbstractDBRecordReader
      edu.yale.cs.hadoopdb.connector.DBRecordReader<T>

Type Parameters:

T -

All Implemented Interfaces:

org.apache.hadoop.mapred.RecordReader<org.apache.hadoop.io.LongWritable,T>

public class DBRecordReader<T extends DBWritable>
extends AbstractDBRecordReader
implements org.apache.hadoop.mapred.RecordReader<org.apache.hadoop.io.LongWritable,T>

Implementation of DBRecordReader for HadoopDB jobs. Records returned include a key (meaningless long) and an value object. All jobs need to specify this class.

Field Summary

private org.apache.hadoop.mapred.JobConf	conf
private DBConfiguration	dbConf
static org.apache.commons.logging.Log	LOG
private java.lang.Class<T>	valueClass

Fields inherited from class edu.yale.cs.hadoopdb.connector.AbstractDBRecordReader

connection, connTime, MAX_CONNECTION_TRIALS, pos, queryTime, results, startTime, statement

Constructor Summary

DBRecordReader(DBConfiguration dbConf, DBInputSplit split, org.apache.hadoop.mapred.JobConf conf)
Constructor requires DBConfiguration to set up DB connection.

Method Summary

T	createValue()
protected java.lang.String	getSqlQuery() Provides a SQL query
boolean	next(org.apache.hadoop.io.LongWritable key, T value) Reads the next record from the result set and passes the result set to the value Object to extract necessary fields.

Methods inherited from class edu.yale.cs.hadoopdb.connector.AbstractDBRecordReader

close, createKey, getConnection, getPos, getProgress, setupDB

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.hadoop.mapred.RecordReader

close, createKey, getPos, getProgress

Field Detail

conf

private org.apache.hadoop.mapred.JobConf conf

dbConf

private DBConfiguration dbConf

LOG

public static final org.apache.commons.logging.Log LOG

valueClass

private java.lang.Class<T extends DBWritable> valueClass

Constructor Detail

DBRecordReader

public DBRecordReader(DBConfiguration dbConf,
                      DBInputSplit split,
                      org.apache.hadoop.mapred.JobConf conf)
               throws java.sql.SQLException

Constructor requires DBConfiguration to set up DB connection.

Throws:

java.sql.SQLException

Method Detail

createValue

public T createValue()

Specified by:

createValue in interface org.apache.hadoop.mapred.RecordReader<org.apache.hadoop.io.LongWritable,T extends DBWritable>

getSqlQuery

protected java.lang.String getSqlQuery()

Provides a SQL query

Specified by:

getSqlQuery in class AbstractDBRecordReader

Returns:

String standard SQL query

next

public boolean next(org.apache.hadoop.io.LongWritable key,
                    T value)
             throws java.io.IOException

Reads the next record from the result set and passes the result set to the value Object to extract necessary fields. Increments the number of rows read in.

Specified by:

next in interface org.apache.hadoop.mapred.RecordReader<org.apache.hadoop.io.LongWritable,T extends DBWritable>

Returns:

false if no more rows exist.

Throws:

java.io.IOException