org.apache.drill.exec.store

Class ImplicitColumnUtils.ImplicitColumns

java.lang.Object

org.apache.drill.exec.store.ImplicitColumnUtils.ImplicitColumns

Enclosing class:

ImplicitColumnUtils

public static class ImplicitColumnUtils.ImplicitColumns
extends Object

This class represents an implicit column in a dataset. These columns are typically used for metadata that is consistent across an entire dataset. A filename for example, or HTTP response codes. It is a good practice to name implicit fields with an underscore so that these field names do not conflict with fields from the user's data. For example _http_response_code. Implicit fields do not appear in star queries so a user must explicitly include them in queries for them to appear.

Constructor Summary

Constructors

Constructor and Description
ImplicitColumns(RowSetLoader rowWriter)

Method Summary

Modifier and Type	Method and Description
void	addImplicitColumn(String fieldName, TypeProtos.MinorType type) Adds an implicit column.
ImplicitColumnUtils.ImplicitColumn	getColumn(String fieldName) Returns a requested ImplicitColumn.
void	writeImplicitColumns() This function writes the data to the implicit columns.

Methods inherited from class java.lang.Object

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

Constructor Detail

ImplicitColumns

public ImplicitColumns(RowSetLoader rowWriter)

Method Detail

addImplicitColumn

public void addImplicitColumn(String fieldName,
                              TypeProtos.MinorType type)

Adds an implicit column. If there already is a column with the same name, the previous column will be overwritten.

Parameters:

fieldName - Name of the implicit column. Recommended that this start with an underscore.

type - The Drill MinorType of the implicit column. Currently only supports simple types.

getColumn

public ImplicitColumnUtils.ImplicitColumn getColumn(String fieldName)

Returns a requested ImplicitColumn. If the column cannot be found, will return null.

Parameters:

fieldName - The field name of the desired column

Returns:

The specific column requested, null if that column does not exist.

writeImplicitColumns

public void writeImplicitColumns()

This function writes the data to the implicit columns. This should be called in the next() method in a batch reader so that the columns get populated. If there are no implicit columns, this function will do nothing, so null checks are not necessary.