org.apache.drill.exec.physical.impl.scan.project

Class ConstantColumnLoader

java.lang.Object

org.apache.drill.exec.physical.impl.scan.project.StaticColumnLoader

org.apache.drill.exec.physical.impl.scan.project.ConstantColumnLoader

public class ConstantColumnLoader
extends StaticColumnLoader

Populate metadata columns either file metadata (AKA "implicit columns") or directory metadata (AKA "partition columns.") In both cases the column type is nullable Varchar and the column value is predefined by the projection planner; this class just copies that value into each row.

The values for the columns appear in the column definitions. This works because the metadata columns are re-resolved for for each file, picking up file-specific values. In some cases, a column might not even have a value (such as a reference to a dirN level that isn't defined for a particular file.

That said, this class is agnostic about the source and meaning of the columns: it only cares that the columns are of type nullable Varchar and that the values are in the column nodes.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	ConstantColumnLoader.ConstantColumnSpec

Field Summary

Fields inherited from class org.apache.drill.exec.physical.impl.scan.project.StaticColumnLoader

loader, vectorCache

Constructor Summary

Constructors

Constructor and Description
ConstantColumnLoader(ResultVectorCache vectorCache, List<? extends ConstantColumnLoader.ConstantColumnSpec> defns)

Method Summary

Modifier and Type	Method and Description
List<? extends ConstantColumnLoader.ConstantColumnSpec>	columns()
VectorContainer	load(int rowCount) Populate static vectors with the defined static values.

Methods inherited from class org.apache.drill.exec.physical.impl.scan.project.StaticColumnLoader

close

Methods inherited from class java.lang.Object

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

Constructor Detail

ConstantColumnLoader

public ConstantColumnLoader(ResultVectorCache vectorCache,
                            List<? extends ConstantColumnLoader.ConstantColumnSpec> defns)

Method Detail

load

public VectorContainer load(int rowCount)

Description copied from class: StaticColumnLoader

Populate static vectors with the defined static values.

Specified by:

load in class StaticColumnLoader

Parameters:

rowCount - number of rows to generate. Must match the row count in the batch returned by the reader

columns

public List<? extends ConstantColumnLoader.ConstantColumnSpec> columns()