com.pervasive.datarush.functions

Class FieldReference

java.lang.Object

com.pervasive.datarush.functions.FieldReference

All Implemented Interfaces:

ScalarValuedFunction

public final class FieldReference
extends Object
implements ScalarValuedFunction

A reference to a field in a record schema. The defined reference returns the value of the the referenced field. These can be used to combine field values with other functions. Note however, that many of the built-in functions provide convenience signatures which do not require direct use of this class.

Constructor Summary

Constructors

Constructor and Description
FieldReference(String name) Defines a reference to the specified field.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(Object obj)
FunctionEvaluator	getEvaluator(RecordValued input, ScalarSettable output) Constructs an instance of an evaluator for the function.
String	getName() Gets the name of the referenced field
Collection<String>	getRequiredFields() Get the input fields required in the function input.
ScalarValued	getSubexpressionEvaluation(EvaluationContext ctx) Constructs an instance of an evaluation of the function in the context of a larger expression.
ScalarTokenType	getUpperBound() Gets the upper bound on the output type of the function.
int	hashCode()
ScalarValuedFunction	mapFieldsToFunctions(Map<String,ScalarValuedFunction> mapping) Creates a new function, equivalent to the given function, but with specified field references mapped to functions.
ScalarValuedFunction	remapFieldReferences(Map<String,String> oldToNewMapping) Creates a new function, equivalent to the given function, but with all field references renamed according to the given mapping.
String	toString()
ScalarTokenType	validateInputType(RecordTokenType inputType) Calculates the actual output type of the function given the specified input type.
static ScalarValuedFunction	value(String fieldName) Defines an expression returning the value of the given field.
static List<ScalarValuedFunction>	values(String... fieldNames) Defines a number of expressions returning the value of a field, one for each given field.

Methods inherited from class java.lang.Object

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

Constructor Detail

FieldReference

public FieldReference(String name)

Defines a reference to the specified field.

Parameters:

name - the name of the field referenced

Method Detail

getName

public String getName()

Gets the name of the referenced field

Returns:

the field name

getUpperBound

public ScalarTokenType getUpperBound()

Description copied from interface: ScalarValuedFunction

Gets the upper bound on the output type of the function. This need not be the exact type of the output, but is expected to be a type to which the actual output type is assignable, as according to TokenType.isAssignableFrom(TokenType).

This value is used to detect type consistency issues as early as possible. It is always valid to return TokenTypeConstant.SCALAR, in which case no type consistency issues can be caught early.

Specified by:

getUpperBound in interface ScalarValuedFunction

Returns:

the most specific type to which any possible return type is assignable.

validateInputType

public ScalarTokenType validateInputType(RecordTokenType inputType)

Description copied from interface: ScalarValuedFunction

Calculates the actual output type of the function given the specified input type.

The type returned must be assignable to the type returned by ScalarValuedFunction.getUpperBound(). If this is not the case, runtime type errors may arise.

Specified by:

validateInputType in interface ScalarValuedFunction

Parameters:

inputType - the type of the record used as input to the function

Returns:

the return type of the function for the given input record schema

getEvaluator

public FunctionEvaluator getEvaluator(RecordValued input,
                             ScalarSettable output)

Description copied from interface: ScalarValuedFunction

Constructs an instance of an evaluator for the function. The evaluator returns the result of the the function applied to the specified input into the given output target.

Implementations may assume that the input and output are known to be compatible with the function. Normally, this method is only invoked by the DataRush framework, which guarantees this is the case. In general, to satisfy this requirement, callers are expected to:

• verify that validateInputType(input.getType()) does not throw an exception
• verify the output type returned is assignable to result.getType()

Failure to meet this contract may result in runtime exceptions.

Specified by:

getEvaluator in interface ScalarValuedFunction

Parameters:

input - the record source to use as context for evaluating the function

output - the buffer into which evaluation results are to be stored

Returns:

an evaluator bound to the provided input and output

getSubexpressionEvaluation

public ScalarValued getSubexpressionEvaluation(EvaluationContext ctx)

Description copied from interface: ScalarValuedFunction

Constructs an instance of an evaluation of the function in the context of a larger expression.

Specified by:

getSubexpressionEvaluation in interface ScalarValuedFunction

Parameters:

ctx - the expression context in which the function is being evaluated as a subexpression

Returns:

an object representing the subexpression's current value

hashCode

public int hashCode()

Description copied from interface: ScalarValuedFunction

ScalarValuedFunctions should override this method in a manner consistent with ScalarValuedFunction.equals(Object).

Specified by:

hashCode in interface ScalarValuedFunction

Overrides:

hashCode in class Object

equals

public boolean equals(Object obj)

Description copied from interface: ScalarValuedFunction

ScalarValuedFunctions should override this method to indicate whether they are equal to another ScalarValuedFunction.

Specified by:

equals in interface ScalarValuedFunction

Overrides:

equals in class Object

toString

public String toString()

Overrides:

toString in class Object

value

public static ScalarValuedFunction value(String fieldName)

Defines an expression returning the value of the given field.

Parameters:

fieldName - the field whose value is to be returned

Returns:

a function evaluating to the specified field's value

values

public static List<ScalarValuedFunction> values(String... fieldNames)

Defines a number of expressions returning the value of a field, one for each given field.

Parameters:

fieldNames - the fields whose values are to be returned

Returns:

functions evaluating to the specified fields' values

getRequiredFields

public Collection<String> getRequiredFields()

Description copied from interface: ScalarValuedFunction

Get the input fields required in the function input. An empty collection implies no specific fields are required.

Specified by:

getRequiredFields in interface ScalarValuedFunction

Returns:

the names of fields which must be present in the record input schema

remapFieldReferences

public ScalarValuedFunction remapFieldReferences(Map<String,String> oldToNewMapping)

Description copied from interface: ScalarValuedFunction

Creates a new function, equivalent to the given function, but with all field references renamed according to the given mapping.

Specified by:

remapFieldReferences in interface ScalarValuedFunction

Parameters:

oldToNewMapping - a mapping from old names to new names. If a name is not present in the given mapping, it will remain as-is.

Returns:

a new function with all field reference renamed appropriately

mapFieldsToFunctions

public ScalarValuedFunction mapFieldsToFunctions(Map<String,ScalarValuedFunction> mapping)

Description copied from interface: ScalarValuedFunction

Creates a new function, equivalent to the given function, but with specified field references mapped to functions.

Specified by:

mapFieldsToFunctions in interface ScalarValuedFunction

Parameters:

mapping - a mapping from field names to functions. If a name is not present in the given mapping, it will remain as-is.

Returns:

a new function with all field reference mapped appropriately