org.apache.flink.api.java.functions

Annotation Type FunctionAnnotation.ConstantFieldsFirstExcept

@Target(value=TYPE)
@Retention(value=RUNTIME)
public static @interface FunctionAnnotation.ConstantFieldsFirstExcept

This annotation declares that a function changes certain fields of its first input value, while leaving all others unmodified and in place in the return value. The annotation is applicable to binary functions, like for example RichFlatJoinFunction, RichCoGroupFunction, or RichCrossFunction.

The following example illustrates a join function that copies fields from the first and second input to the return value:

 \@ConstantFieldsFirstExcept("1")
 public class MyJoin extends JoinFunction, Tuple2, Tuple3>
 {
     public Tuple3 map(Tuple3 first, Tuple2 second) {
         return Tuple3(first.f0, second.f1, first.f2);
     }
 }
 

The annotation takes one String array specifying the positions of the input types that do not remain constant. When this annotation is used, it is assumed that all other values remain at the same position in input and output. To model more complex situations use the FunctionAnnotation.ConstantFieldss annotation.

This annotation is mutually exclusive with the FunctionAnnotation.ConstantFieldsFirst

If neither this annotation, nor the FunctionAnnotation.ConstantFieldsFirst annotation are set, it is assumed that no field in the first input is forwarded/copied unmodified.

See Also:

FunctionAnnotation.ConstantFieldsFirst, FunctionAnnotation.ConstantFieldsSecond, FunctionAnnotation.ConstantFieldsSecondExcept

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
String[]	value

Element Detail

value

public abstract String[] value