org.apache.calcite.rel.metadata

Class ReflectiveRelMetadataProvider

java.lang.Object

org.apache.calcite.rel.metadata.ReflectiveRelMetadataProvider

All Implemented Interfaces:

RelMetadataProvider, ReflectiveVisitor

public class ReflectiveRelMetadataProvider
extends Object
implements RelMetadataProvider, ReflectiveVisitor

Implementation of the RelMetadataProvider interface that dispatches metadata methods to methods on a given object via reflection.

The methods on the target object must be public and non-static, and have the same signature as the implemented metadata method except for an additional first parameter of type RelNode or a sub-class. That parameter gives this provider an indication of that relational expressions it can handle.

For an example, see RelMdColumnOrigins.SOURCE.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ReflectiveRelMetadataProvider(Map<Class<RelNode>,com.google.common.base.Function<RelNode,Metadata>> map, Class<?> metadataClass0) Creates a ReflectiveRelMetadataProvider.

Method Summary

Methods

Modifier and Type	Method and Description
com.google.common.base.Function<RelNode,Metadata>	apply(Class<? extends RelNode> relClass, Class<? extends Metadata> metadataClass) Retrieves metadata of a particular type and for a particular sub-class of relational expression.
static RelMetadataProvider	reflectiveSource(Method method, Object target) Returns an implementation of RelMetadataProvider that scans for methods with a preceding argument.
static RelMetadataProvider	reflectiveSource(Object target, Method... methods) Returns a reflective metadata provider that implements several methods.

Methods inherited from class java.lang.Object

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

Constructor Detail

ReflectiveRelMetadataProvider

protected ReflectiveRelMetadataProvider(Map<Class<RelNode>,com.google.common.base.Function<RelNode,Metadata>> map,
                             Class<?> metadataClass0)

Creates a ReflectiveRelMetadataProvider.

Parameters:

map - Map

metadataClass0 - Metadata class

Method Detail

reflectiveSource

public static RelMetadataProvider reflectiveSource(Method method,
                                   Object target)

Returns an implementation of RelMetadataProvider that scans for methods with a preceding argument.

For example, BuiltInMetadata.Selectivity has a method BuiltInMetadata.Selectivity.getSelectivity(org.apache.calcite.rex.RexNode). A class

 class RelMdSelectivity {
   public Double getSelectivity(Union rel, RexNode predicate) { }
   public Double getSelectivity(Filter rel, RexNode predicate) { }
 

provides implementations of selectivity for relational expressions that extend Union or Filter.

reflectiveSource

public static RelMetadataProvider reflectiveSource(Object target,
                                   Method... methods)

Returns a reflective metadata provider that implements several methods.

apply

public com.google.common.base.Function<RelNode,Metadata> apply(Class<? extends RelNode> relClass,
                                                      Class<? extends Metadata> metadataClass)

Description copied from interface: RelMetadataProvider

Retrieves metadata of a particular type and for a particular sub-class of relational expression.

The object returned is a function. It can be applied to a relational expression of the given type to create a metadata object.

For example, you might call

 RelMetadataProvider provider;
 LogicalFilter filter;
 RexNode predicate;
 Function<RelNode, Metadata> function =
   provider.apply(LogicalFilter.class, Selectivity.class};
 Selectivity selectivity = function.apply(filter);
 Double d = selectivity.selectivity(predicate);
 

Specified by:

apply in interface RelMetadataProvider

Parameters:

relClass - Type of relational expression

metadataClass - Type of metadata

Returns:

Function that will field a metadata instance; or null if this provider cannot supply metadata of this type