org.apache.calcite.rel.metadata

Interface RelMetadataProvider

All Known Implementing Classes:

CachingRelMetadataProvider, ChainedRelMetadataProvider, DefaultRelMetadataProvider, ReflectiveRelMetadataProvider, VolcanoRelMetadataProvider

public interface RelMetadataProvider

RelMetadataProvider defines an interface for obtaining metadata about relational expressions. This interface is weakly-typed and is not intended to be called directly in most contexts; instead, use a strongly-typed facade such as RelMetadataQuery.

For background and motivation, see wiki.

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.

Method Detail

apply

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.

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);
 

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