org.apache.crunch.types

Interface PType<T>

All Superinterfaces:

Serializable

All Known Subinterfaces:

PTableType<K,V>

All Known Implementing Classes:

AvroType, PGroupedTableType, WritableType

public interface PType<T>
extends Serializable

A PType defines a mapping between a data type that is used in a Crunch pipeline and a serialization and storage format that is used to read/write data from/to HDFS. Every PCollection has an associated PType that tells Crunch how to read/write data from that PCollection.

Method Summary

Modifier and Type	Method and Description
ReadableSource<T>	createSourceTarget(org.apache.hadoop.conf.Configuration conf, org.apache.hadoop.fs.Path path, Iterable<T> contents, int parallelism) Returns a ReadableSource that contains the data in the given Iterable.
Converter	getConverter()
ReadableSourceTarget<T>	getDefaultFileSource(org.apache.hadoop.fs.Path path) Returns a SourceTarget that is able to read/write data using the serialization format specified by this PType.
T	getDetachedValue(T value) Returns a copy of a value (or the value itself) that can safely be retained.
PTypeFamily	getFamily() Returns the PTypeFamily that this PType belongs to.
MapFn<Object,T>	getInputMapFn()
MapFn<T,Object>	getOutputMapFn()
List<PType>	getSubTypes() Returns the sub-types that make up this PType if it is a composite instance, such as a tuple.
Class<T>	getTypeClass() Returns the Java type represented by this PType.
void	initialize(org.apache.hadoop.conf.Configuration conf) Initialize this PType for use within a DoFn.

Method Detail

getTypeClass

Class<T> getTypeClass()

Returns the Java type represented by this PType.

getFamily

PTypeFamily getFamily()

Returns the PTypeFamily that this PType belongs to.

getInputMapFn

MapFn<Object,T> getInputMapFn()

getOutputMapFn

MapFn<T,Object> getOutputMapFn()

getConverter

Converter getConverter()

initialize

void initialize(org.apache.hadoop.conf.Configuration conf)

Initialize this PType for use within a DoFn. This generally only needs to be called when using a PType for getDetachedValue(Object).

Parameters:

conf - Configuration object

See Also:

getDetachedValue(Object)

getDetachedValue

T getDetachedValue(T value)

Returns a copy of a value (or the value itself) that can safely be retained.

This is useful when iterable values being processed in a DoFn (via a reducer) need to be held on to for more than the scope of a single iteration, as a reducer (and therefore also a DoFn that has an Iterable as input) re-use deserialized values. More information on object reuse is available in the DoFn class documentation.

Parameters:

value - The value to be deep-copied

Returns:

A deep copy of the input value

getDefaultFileSource

ReadableSourceTarget<T> getDefaultFileSource(org.apache.hadoop.fs.Path path)

Returns a SourceTarget that is able to read/write data using the serialization format specified by this PType.

createSourceTarget

ReadableSource<T> createSourceTarget(org.apache.hadoop.conf.Configuration conf,
                                     org.apache.hadoop.fs.Path path,
                                     Iterable<T> contents,
                                     int parallelism)
                              throws IOException

Returns a ReadableSource that contains the data in the given Iterable.

Parameters:

conf - The Configuration to use

path - The path to write the data to

contents - The contents to write

parallelism - The desired parallelism

Returns:

A new instance of ReadableSource

Throws:

IOException

getSubTypes

List<PType> getSubTypes()

Returns the sub-types that make up this PType if it is a composite instance, such as a tuple.