Module datarush.library
Package com.pervasive.datarush.functions

Class 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 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.

      • 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

      • 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