cascading.operation.expression
Class ExpressionFunction

java.lang.Object
  cascading.operation.BaseOperation<ScriptOperation.Context>
      cascading.operation.expression.ScriptOperation
          cascading.operation.expression.ExpressionOperation
              cascading.operation.expression.ExpressionFunction

All Implemented Interfaces:

DeclaresResults, Function<ScriptOperation.Context>, Operation<ScriptOperation.Context>, Serializable

public class ExpressionFunction
extends ExpressionOperation
implements Function<ScriptOperation.Context>

Class ExpressionFunction dynamically resolves a given expression using argument Tuple values. This Function is based on the Janino compiler.

Specifically this function uses the ExpressionEvaluator, thus the syntax from that class is inherited here.

An expression may use field names directly as parameters in the expression, or field positions with the syntax "$n", where n is an integer.

Given an argument tuple with the fields "a" and "b", the following expression returns true:
a + b == $0 + $1

Further, the types of the tuple elements will be coerced into the given parameterTypes. Regardless of the actual tuple element values, they will be converted to the types expected by the expression.

Field names used in the expression should be valid Java variable names; for example, '+' or '-' are not allowed. Also the use of a field name that begins with an upper-case character is likely to fail and should be avoided.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class cascading.operation.expression.ScriptOperation

ScriptOperation.Context

Field Summary

Fields inherited from class cascading.operation.expression.ScriptOperation

block, parameterNames, parameterTypes, returnType

Fields inherited from class cascading.operation.BaseOperation

fieldDeclaration, numArgs, trace

Fields inherited from interface cascading.operation.Operation

ANY

Constructor Summary

ExpressionFunction(Fields fieldDeclaration, String expression)
Constructor ExpressionFunction creates a new ExpressionFunction instance.

ExpressionFunction(Fields fieldDeclaration, String expression, Class parameterType)
Constructor ExpressionFunction creates a new ExpressionFunction instance.

ExpressionFunction(Fields fieldDeclaration, String expression, String[] parameterNames, Class[] parameterTypes)
Constructor ExpressionFunction creates a new ExpressionFunction instance.

Method Summary

void	operate(FlowProcess flowProcess, FunctionCall<ScriptOperation.Context> functionCall) Method operate provides the implementation of this Function.

Methods inherited from class cascading.operation.expression.ExpressionOperation

getEvaluator, getExpression, guessParameterNames

Methods inherited from class cascading.operation.expression.ScriptOperation

equals, evaluate, getBlock, getParameterNames, getParameterTypes, getReturnType, hashCode, prepare

Methods inherited from class cascading.operation.BaseOperation

cleanup, flush, getFieldDeclaration, getNumArgs, getTrace, isSafe, printOperationInternal, toString, toStringInternal

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface cascading.operation.Operation

cleanup, flush, getFieldDeclaration, getNumArgs, isSafe, prepare

Constructor Detail

ExpressionFunction

@ConstructorProperties(value={"fieldDeclaration","expression"})
public ExpressionFunction(Fields fieldDeclaration,
                                                     String expression)

Constructor ExpressionFunction creates a new ExpressionFunction instance.

This constructor assumes the given expression expects no input parameters. This is useful when inserting random numbers for example, (int) (Math.random() * Integer.MAX_VALUE) .

Parameters:

fieldDeclaration - of type Fields

expression - of type String

ExpressionFunction

@ConstructorProperties(value={"fieldDeclaration","expression","parameterType"})
public ExpressionFunction(Fields fieldDeclaration,
                                                     String expression,
                                                     Class parameterType)

Constructor ExpressionFunction creates a new ExpressionFunction instance.

This constructor assumes all parameter are of the same type.

Parameters:

fieldDeclaration - of type Fields

expression - of type String

parameterType - of type Class

ExpressionFunction

@ConstructorProperties(value={"fieldDeclaration","expression","parameterNames","parameterTypes"})
public ExpressionFunction(Fields fieldDeclaration,
                                                     String expression,
                                                     String[] parameterNames,
                                                     Class[] parameterTypes)

Constructor ExpressionFunction creates a new ExpressionFunction instance.

This constructor expects all parameter type names to be declared with their types. Positional parameters must be named the same as in the given expression with the "$" sign prepended.

Parameters:

fieldDeclaration - of type Fields

expression - of type String

parameterNames - of type String[]

parameterTypes - of type Class[]

Method Detail

operate

public void operate(FlowProcess flowProcess,
                    FunctionCall<ScriptOperation.Context> functionCall)

Description copied from interface: Function

Method operate provides the implementation of this Function.

Specified by:

operate in interface Function<ScriptOperation.Context>

Parameters:

flowProcess - of type FlowProcess

functionCall - of type FunctionCall