Package org.apache.calcite.rel.metadata

Interface RelMetadataProvider

All Known Implementing Classes:
CachingRelMetadataProvider, ChainedRelMetadataProvider, DefaultRelMetadataProvider, JaninoRelMetadataProvider, 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.

If your provider is not a singleton, we recommend that you implement Object.equals(Object) and Object.hashCode() methods. This makes the cache of JaninoRelMetadataProvider more effective.

  • Method Details

    • apply

      @Deprecated <@Nullable M extends @Nullable Metadata> @Nullable UnboundMetadata<M> apply(Class<? extends RelNode> relClass, Class<? extends @Nullable M> metadataClass)
      Deprecated.
      Use RelMetadataQuery.
      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

    • handlers

      @Deprecated <M extends Metadata> com.google.common.collect.Multimap<Method,MetadataHandler<M>> handlers(MetadataDef<M> def)
      Deprecated.

    • handlers

      List<MetadataHandler<?>> handlers(Class<? extends MetadataHandler<?>> handlerClass)
      Retrieves a list of MetadataHandler for implements a particular MetadataHandler.class. The resolution order is specificity of the relNode class, with preference given to handlers that occur earlier in the list.

      For instance, given a return list of {A, B, C} where A implements RelNode and Scan, B implements Scan, and C implements LogicalScan and Filter.

      Scan dispatches to a.method(Scan); LogicalFilter dispatches to c.method(Filter); LogicalScan dispatches to c.method(LogicalScan); Aggregate dispatches to a.method(RelNode).

      The behavior is undefined if the class hierarchy for dispatching is not a tree.