Package stream.nebula.operators

Class ProjectionOperator

java.lang.Object

stream.nebula.operators.Operator

stream.nebula.operators.ProjectionOperator

public class ProjectionOperator
extends Operator

This Operator encodes a Query.project(stream.nebula.expression.FieldExpression...) operation.

The Query.project(stream.nebula.expression.FieldExpression...) also allows to rename the attributes in the result stream, using FieldAccessExpression.as(java.lang.String), as in the following code:

     Query query = QueryFactory.from("source_name").project(
          attribute("field1"),                    # Use original attribute name 'field1' in projected stream.
          attribute("field2").as("new_name"));    # Rename attribute 'field2' to 'new_name' in projected stream.
 

Field Summary

Fields inherited from class stream.nebula.operators.Operator

childOperator

Constructor Summary

Constructors

Constructor	Description
ProjectionOperator(@NonNull Operator childOperator, @NonNull FieldExpression[] attributes)	Create a new ProjectOperator.

Method Summary

Modifier and Type	Method	Description
java.util.List<FieldExpression>	getProjectedAttributes()	Access the list of projected attributes.

Methods inherited from class stream.nebula.operators.Operator

getChildOperator

Methods inherited from class java.lang.Object

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

Constructor Detail

ProjectionOperator

public ProjectionOperator(@NonNull Operator childOperator,
                          @NonNull FieldExpression[] attributes)
                   throws java.lang.IllegalStateException

Create a new ProjectOperator.

Parameters:

childOperator - The previous operator in the operator chain of Query instance.

attributes - A variable list of projected attributes.

Throws:

java.lang.IllegalStateException

Method Detail

getProjectedAttributes

public java.util.List<FieldExpression> getProjectedAttributes()

Access the list of projected attributes.

Returns:

The projected attributes specified in the call to Query.project(stream.nebula.expression.FieldExpression...).