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/*
* Copyright 2017 ObjectBox Ltd. All rights reserved.
*
* 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 io.objectbox.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import io.objectbox.annotation.apihint.Beta;
/**
* Defines a backlink relation, which is based on another relation reversing the direction.
*
* Example (to-one relation): one "Order" references one "Customer".
* The backlink to this is a to-many in the reverse direction: one "Customer" has a number of "Order"s.
*
* Example (to-many relation): one "Teacher" references multiple "Student"s.
* The backlink to this: one "Student" has a number of "Teacher"s.
*
* Note: changes made to a backlink relation based on a to-many relation are ignored.
*/
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.FIELD)
@Beta
public @interface Backlink {
/**
* Name of the relation the backlink should be based on (e.g. name of a ToOne or ToMany property in the target entity).
* Can be left empty if there is just a single relation from the target to the source entity.
*/
String to() default "";
}