net.java.ao.Polymorphic Maven / Gradle / Ivy
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/*
* Copyright 2007 Daniel Spiewak
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.java.ao;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Tags a given entity type as polymorphically abstract. This means that
* the given type will not peer to any table, but rather represent
* a polymorphic supertype to other entities (entities which extend the
* given interface). Unlike conventional inheritence, which also causes
* the supertype to not peer to a table, polymorphic type inheritence
* allows instances of the subtype to be stored in the database into fields
* which are "typed" in ActiveObjects as the supertype. All of this is
* really much simpler than it sounds:
*
* public interface Person extends Entity {
* public Computer getComputer();
* public void setComputer(Computer computer);
* }
*
* @Polymorphic
* public interface Computer extends Entity {
* public float getSpeed();
* public void setSpeed(float speed);
* }
*
* public interface Mac extends Computer {}
* public interface PC extends Computer {}
*
* In this case, Computer does not correspond with any table in
* the database. Likewise, Person has no foreign keys for the
* corresponding field to getComputer(). When an entity type is
* polymorphic, its subtypes can be used polymorphically as they are in
* Person. This is essentially the conceptual analog of an
* abstract class when mapped into the database.
*
* @author Daniel Spiewak
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Polymorphic {
}