datafu.pig.util

Class ContextualEvalFunc<T>

java.lang.Object

org.apache.pig.EvalFunc<T>

datafu.pig.util.ContextualEvalFunc<T>

Type Parameters:

T - the type the eval function returns

Direct Known Subclasses:

AliasableEvalFunc, EmptyBagToNullFields, SimpleEvalFunc

public abstract class ContextualEvalFunc<T>
extends org.apache.pig.EvalFunc<T>

An abstract class which enables UDFs to store instance properties on the front end which will be available on the back end. For example, you can override the onSchemaReady hook method to set properties at front-end (i.e. at launch time) which will be available when exec() is called (on the workers themselves.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.pig.EvalFunc

org.apache.pig.EvalFunc.SchemaType

Field Summary

Fields inherited from class org.apache.pig.EvalFunc

log, pigLogger, reporter, returnType

Constructor Summary

Constructors

Constructor and Description
ContextualEvalFunc()

Method Summary

Methods

Modifier and Type	Method and Description
protected java.util.Properties	getContextProperties() Helper method to return the context properties for this class
protected java.lang.String	getInstanceName()
protected java.util.Properties	getInstanceProperties() Helper method to return the context properties for this instance of this class
protected void	onReady(org.apache.pig.impl.logicalLayer.schema.Schema in_schema, org.apache.pig.impl.logicalLayer.schema.Schema out_schema) Hook method, called once the input and output schema are prepared.
org.apache.pig.impl.logicalLayer.schema.Schema	outputSchema(org.apache.pig.impl.logicalLayer.schema.Schema in_schema) Override outputSchema only to add the onSchemaReady hook method.
void	setUDFContextSignature(java.lang.String signature)

Methods inherited from class org.apache.pig.EvalFunc

allowCompileTimeCalculation, exec, finish, getArgToFuncMapping, getCacheFiles, getInputSchema, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, getSchemaType, getShipFiles, isAsynchronous, progress, setInputSchema, setPigLogger, setReporter, warn

Methods inherited from class java.lang.Object

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

Constructor Detail

ContextualEvalFunc

public ContextualEvalFunc()

Method Detail

setUDFContextSignature

public void setUDFContextSignature(java.lang.String signature)

Overrides:

setUDFContextSignature in class org.apache.pig.EvalFunc<T>

getContextProperties

protected java.util.Properties getContextProperties()

Helper method to return the context properties for this class

Returns:

context properties

getInstanceProperties

protected java.util.Properties getInstanceProperties()

Helper method to return the context properties for this instance of this class

Returns:

instances properties

getInstanceName

protected java.lang.String getInstanceName()

Returns:

the name of this instance corresponding to the UDF Context Signature

See Also:

setUDFContextSignature(String)

onReady

protected void onReady(org.apache.pig.impl.logicalLayer.schema.Schema in_schema,
           org.apache.pig.impl.logicalLayer.schema.Schema out_schema)

Hook method, called once the input and output schema are prepared. Subclasses may override to set properties on the front end (i.e. at script run time) that may be played with later (e.g. at execution time). Child classes must (a) call super.onReady(in_schema, out_schema) so that the hook chains, and (b) not mess with the schema.

Parameters:

in_schema - input schema

out_schema - output schema

outputSchema

public org.apache.pig.impl.logicalLayer.schema.Schema outputSchema(org.apache.pig.impl.logicalLayer.schema.Schema in_schema)

Override outputSchema only to add the onSchemaReady hook method. In all other respects delegates to the superclass outputSchema preparation.

Overrides:

outputSchema in class org.apache.pig.EvalFunc<T>

Parameters:

in_schema - input schema

Returns:

call to super.outputSchema