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

Interface MetadataManager

All Known Implementing Classes:

ImplicitColumnManager, NoOpMetadataManager

public interface MetadataManager

Queries can contain a wildcard (*), table columns, or special system-defined columns (the file metadata columns AKA implicit columns, the `columns` column of CSV, etc.).

This class provides a generalized way of handling such extended columns. That is, this handles metadata for columns defined by the scan or file; columns defined by the table (the actual data metadata) is handled elsewhere.

Objects of this interface are driven by the projection processing framework which provides a vector cache from which to obtain materialized columns. The implementation must provide a projection parser to pick out the columns which this object handles.

A better name might be ImplicitMetadataManager to signify that this is about metadata other than table columns.

Method Summary

Modifier and Type	Method and Description
void	bind(ResultVectorCache vectorCache)
void	close() Event indicating the end of a scan.
void	define() Define (materialize) the columns which this manager represents.
void	endFile() Event indicating the end of a file (or other data source.)
void	load(int rowCount) Load data into the custom columns, if needed (such as for null or implicit columns.)
ScanLevelProjection.ScanProjectionParser	projectionParser()
ReaderLevelProjection.ReaderProjectionResolver	resolver()

Method Detail

bind

void bind(ResultVectorCache vectorCache)

projectionParser

ScanLevelProjection.ScanProjectionParser projectionParser()

resolver

ReaderLevelProjection.ReaderProjectionResolver resolver()

define

void define()

Define (materialize) the columns which this manager represents.

load

void load(int rowCount)

Load data into the custom columns, if needed (such as for null or implicit columns.)

Parameters:

rowCount - number of rows read into a batch.

endFile

void endFile()

Event indicating the end of a file (or other data source.)

close

void close()

Event indicating the end of a scan.