org.apache.calcite.plan

Interface RelTrait

All Known Subinterfaces:

Convention, RelCollation, RelDistribution, RelMultipleTrait

All Known Implementing Classes:

BindableConvention, Convention.Impl, EnumerableConvention, InterpretableConvention, JdbcConvention, RelCollationImpl

public interface RelTrait

RelTrait represents the manifestation of a relational expression trait within a trait definition. For example, a CallingConvention.JAVA is a trait of the ConventionTraitDef trait definition.

Note about equals() and hashCode()

If all instances of RelTrait for a particular RelTraitDef are defined in an enum and no new RelTraits can be introduced at runtime, you need not override hashCode() and equals(Object). If, however, new RelTrait instances are generated at runtime (e.g. based on state external to the planner), you must implement hashCode() and equals(Object) for proper canonization of your RelTrait objects.

Method Summary

Modifier and Type	Method and Description
default <T extends RelTrait> T	apply(Mappings.TargetMapping mapping) Applies a mapping to this trait.
boolean	equals(@Nullable Object o) See note about equals() and hashCode().
RelTraitDef	getTraitDef() Returns the RelTraitDef that defines this RelTrait.
int	hashCode() See note about equals() and hashCode().
default boolean	isDefault() Returns whether this trait is the default trait value.
void	register(RelOptPlanner planner) Registers a trait instance with the planner.
boolean	satisfies(RelTrait trait) Returns whether this trait satisfies a given trait.
String	toString() Returns a succinct name for this trait.

Method Detail

getTraitDef

RelTraitDef getTraitDef()

Returns the RelTraitDef that defines this RelTrait.

Returns:

the RelTraitDef that defines this RelTrait

hashCode

int hashCode()

See note about equals() and hashCode().

Overrides:

hashCode in class Object

equals

boolean equals(@Nullable Object o)

See note about equals() and hashCode().

Overrides:

equals in class Object

satisfies

boolean satisfies(RelTrait trait)

Returns whether this trait satisfies a given trait.

A trait satisfies another if it is the same or stricter. For example, ORDER BY x, y satisfies ORDER BY x.

A trait's satisfies relation must be a partial order (reflexive, anti-symmetric, transitive). Many traits cannot be "loosened"; their satisfies is an equivalence relation, where only X satisfies X.

If a trait has multiple values (see RelCompositeTrait) a collection (T0, T1, ...) satisfies T if any Ti satisfies T.

Parameters:

trait - Given trait

Returns:

Whether this trait subsumes a given trait

toString

String toString()

Returns a succinct name for this trait. The planner may use this String to describe the trait.

Overrides:

toString in class Object

register

void register(RelOptPlanner planner)

Registers a trait instance with the planner.

This is an opportunity to add rules that relate to that trait. However, typical implementations will do nothing.

Parameters:

planner - Planner

apply

default <T extends RelTrait> T apply(Mappings.TargetMapping mapping)

Applies a mapping to this trait.

Some traits may be changed if the columns order is changed by a mapping of the Project operator.

For example, if relation SELECT a, b ORDER BY a, b is sorted by columns [0, 1], then the project SELECT b, a over this relation will be sorted by columns [1, 0]. In the same time project SELECT b will not be sorted at all because it doesn't contain the collation prefix and this method will return an empty collation.

Other traits are independent from the columns remapping. For example Convention or RelDistributions.SINGLETON.

Parameters:

mapping - Mapping

Returns:

trait with mapping applied

isDefault

default boolean isDefault()

Returns whether this trait is the default trait value.