com.hazelcast.org.apache.calcite.plan.RelTrait Maven / Gradle / Ivy
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* the License. You may obtain a copy of the License at
*
* http://www.apache.com.hazelcast.org.licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
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package com.hazelcast.org.apache.calcite.plan;
import com.hazelcast.org.apache.calcite.rel.RelDistributions;
import com.hazelcast.org.apache.calcite.rel.core.Project;
import com.hazelcast.org.apache.calcite.util.mapping.Mappings;
/**
* RelTrait represents the manifestation of a relational expression trait within
* a trait definition. For example, a {@code CallingConvention.JAVA} is a trait
* of the {@link ConventionTraitDef} trait definition.
*
* Note about equals() and hashCode()
*
* If all instances of RelTrait for a particular RelTraitDef are defined in
* an {@code enum} and no new RelTraits can be introduced at runtime, you need
* not override {@link #hashCode()} and {@link #equals(Object)}. If, however,
* new RelTrait instances are generated at runtime (e.g. based on state external
* to the planner), you must implement {@link #hashCode()} and
* {@link #equals(Object)} for proper {@link RelTraitDef#canonize canonization}
* of your RelTrait objects.
*/
public interface RelTrait {
//~ Methods ----------------------------------------------------------------
/**
* Returns the RelTraitDef that defines this RelTrait.
*
* @return the RelTraitDef that defines this RelTrait
*/
RelTraitDef getTraitDef();
/**
* See note about equals() and hashCode().
*/
int hashCode();
/**
* See note about equals() and hashCode().
*/
boolean equals(Object o);
/**
* Returns whether this trait satisfies a given trait.
*
* A trait satisfies another if it is the same or stricter. For example,
* {@code ORDER BY x, y} satisfies {@code ORDER BY x}.
*
*
A trait's {@code satisfies} relation must be a partial order (reflexive,
* anti-symmetric, transitive). Many traits cannot be "loosened"; their
* {@code satisfies} is an equivalence relation, where only X satisfies X.
*
*
If a trait has multiple values
* (see {@link com.hazelcast.org.apache.calcite.plan.RelCompositeTrait})
* a collection (T0, T1, ...) satisfies T if any Ti satisfies T.
*
* @param trait Given trait
* @return Whether this trait subsumes a given trait
*/
boolean satisfies(RelTrait trait);
/**
* Returns a succinct name for this trait. The planner may use this String
* to describe the trait.
*/
String toString();
/**
* 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.
*
* @param planner Planner
*/
void register(RelOptPlanner planner);
/**
* Applies a mapping to this trait.
*
* Some traits may be changed if the columns order is changed by a mapping of the
* {@link Project} operator.
*
* For example, if relation {@code SELECT a, b ORDER BY a, b} is sorted by columns [0, 1],
* then the project {@code SELECT b, a} over this relation will be sorted by columns [1, 0].
* In the same time project {@code 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 {@link Convention} or
* {@link RelDistributions#SINGLETON}.
*
* @param mapping Mapping
* @return trait with mapping applied
*/
default T apply(Mappings.TargetMapping mapping) {
return (T) this;
}
}