org.apache.drill.exec.store.enumerable

Class EnumerableRecordReader

java.lang.Object

org.apache.drill.exec.store.enumerable.EnumerableRecordReader

All Implemented Interfaces:

ManagedReader<SchemaNegotiator>

public class EnumerableRecordReader
extends Object
implements ManagedReader<SchemaNegotiator>

ManagedReader implementation that compiles and executes specified code, calls the method on it for obtaining the values, and reads the results using column converters.

Constructor Summary

Constructors

Constructor and Description
EnumerableRecordReader(List<SchemaPath> columns, Map<String,Integer> fieldsMap, String code, String schemaPath)

Method Summary

Modifier and Type	Method and Description
void	close() Release resources.
boolean	next() Read the next batch.
boolean	open(SchemaNegotiator negotiator) Setup the record reader.

Methods inherited from class java.lang.Object

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

Constructor Detail

EnumerableRecordReader

public EnumerableRecordReader(List<SchemaPath> columns,
                              Map<String,Integer> fieldsMap,
                              String code,
                              String schemaPath)

Method Detail

open

public boolean open(SchemaNegotiator negotiator)

Description copied from interface: ManagedReader

Setup the record reader. Called just before the first call to next(). Allocate resources here, not in the constructor. Example: open files, allocate buffers, etc.

Specified by:

open in interface ManagedReader<SchemaNegotiator>

Parameters:

negotiator - mechanism to negotiate select and table schemas, then create the row set reader used to load data into value vectors

Returns:

true if the reader is open and ready to read (possibly no) rows. false for a "soft" failure in which no schema or data is available, but the scanner should not fail, it should move onto another reader

next

public boolean next()

Description copied from interface: ManagedReader

Read the next batch. Reading continues until either EOF, or until the mutator indicates that the batch is full. The batch is considered valid if it is non-empty. Returning true with an empty batch is valid, and is helpful on the very first batch (returning schema only.) An empty batch with a false return code indicates EOF and the batch will be discarded. A non-empty batch along with a false return result indicates a final, valid batch, but that EOF was reached and no more data is available.

This somewhat complex protocol avoids the need to allocate a final batch just to find out that no more data is available; it allows EOF to be returned along with the final batch.

Specified by:

next in interface ManagedReader<SchemaNegotiator>

Returns:

true if more data may be available (and so next() should be called again, false to indicate that EOF was reached

close

public void close()

Description copied from interface: ManagedReader

Release resources. Called just after a failure, when the scanner is cancelled, or after next() returns EOF. Release all resources and close files. Guaranteed to be called if open() returns normally; will not be called if open() throws an exception.

Specified by:

close in interface ManagedReader<SchemaNegotiator>