org.eigenbase.rel.metadata
Class ReflectiveRelMetadataProvider

java.lang.Object
  org.eigenbase.rel.metadata.ReflectiveRelMetadataProvider

All Implemented Interfaces:

RelMetadataProvider, ReflectiveVisitor

Direct Known Subclasses:

FarragoRelMetadataProvider, FarragoTestPersonalityFactory.FarragoTestRelMetadataProvider, FtrsDataServer.FtrsRelMetadataProvider, LoptMetadataProvider, MedJdbcMetadataProvider, RelMdColumnOrigins, RelMdColumnUniqueness, RelMdDistinctRowCount, RelMdExplainVisibility, RelMdPercentageOriginalRows, RelMdPopulationSize, RelMdRowCount, RelMdSelectivity, RelMdUniqueKeys

public abstract class ReflectiveRelMetadataProvider
extends Object
implements RelMetadataProvider, ReflectiveVisitor

ReflectiveRelMetadataProvider provides an abstract base for reflective implementations of the RelMetadataProvider interface. For an example, see DefaultRelMetadataProvider.

TODO jvs 28-Mar-2006: most of this should probably be refactored into ReflectUtil.

Version:

$Id: //open/dev/farrago/src/org/eigenbase/rel/metadata/ReflectiveRelMetadataProvider.java#9 $

Author:

John V. Sichi

Field Summary

private Map<String,List<Class>>	parameterTypeMap
private ReflectiveVisitDispatcher<ReflectiveRelMetadataProvider,RelNode>	visitDispatcher

Constructor Summary

protected

ReflectiveRelMetadataProvider() Creates a ReflectiveRelMetadataProvider.

Method Summary

Object	getRelMetadata(RelNode rel, String metadataQueryName, Object[] args) Retrieves metadata about a relational expression.
protected void	mapParameterTypes(String metadataQueryName, List<Class> parameterTypes) Maps the parameter type signature to look up for a given metadata query.

Methods inherited from class java.lang.Object

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

Field Detail

parameterTypeMap

private final Map<String,List<Class>> parameterTypeMap

visitDispatcher

private final ReflectiveVisitDispatcher<ReflectiveRelMetadataProvider,RelNode> visitDispatcher

Constructor Detail

ReflectiveRelMetadataProvider

protected ReflectiveRelMetadataProvider()

Creates a ReflectiveRelMetadataProvider.

Method Detail

mapParameterTypes

protected void mapParameterTypes(String metadataQueryName,
                                 List<Class> parameterTypes)

Maps the parameter type signature to look up for a given metadata query.

Parameters:

metadataQueryName - name of metadata query to map

parameterTypes - argument types (beyond the overloaded rel type) to map

getRelMetadata

public Object getRelMetadata(RelNode rel,
                             String metadataQueryName,
                             Object[] args)

Description copied from interface: RelMetadataProvider

Retrieves metadata about a relational expression.

Specified by:

getRelMetadata in interface RelMetadataProvider

Parameters:

rel - relational expression of interest

metadataQueryName - name of metadata query to invoke

args - arguments to metadata query (expected number and type depend on query name; must have well-defined hashCode/equals for use by caching); null can be used instead of empty array

Returns:

metadata result (actual type depends on query name), or null if the provider cannot answer the given query/rel combination; it is better to return null than to return a possibly incorrect answer