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/*
* Copyright 2006 Amazon Technologies, Inc. or its affiliates.
* Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
* of Amazon Technologies, Inc. or its affiliates. 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 com.amazon.carbonado;
import java.lang.annotation.*;
/**
* Identifies a {@link Storable} property as defining a join relationship
* with another Storable type. Joins can also refer to their own enclosing
* class or interface.
* <p>
* To complete the join, lists of internal and external properties may be
* supplied. If these lists are not supplied, then join is "natural", and the
* properties are determined automatically. When the lists are specified, the
* join is "explicit". Natural joins are merely a convenience; they can always
* be replaced by an explicit join.
* <p>
* The lists used for explicit joins must have the same length, and each must
* have at least one element. Each element in the internal list must refer to
* a property defined in this property's class or interface, and each element
* in the external list must refer to a matching property defined in the joined
* type. The matched up property pairs must not themselves be join properties,
* and they must be compatible with each other.
* <p>
* If the join is made to external properties which do not completely specify a
* primary key, then the type of the join property must be a {@link Query} of
* the joined type. When the type is a Query, a property mutator method cannot
* be defined. The returned query has all of the "with" parameters filled in.
* <p>
* With a natural join, the internal and external properties are deduced by
* examining the type of the referenced join property. If the type is a Query,
* then the internal and external properties are set to match this property's
* primary key. The referenced join property (specified as a parameterized type
* to Query) must have properties matching name and type of this property's
* primary key.
* <p>
* If a natural join's property type is not defined by a Query, then the
* internal and external properties are set to match the referenced property's
* primary key. This join property must have properties matching name and type
* of the referenced property's primary key.
*
* <p>Example:<pre>
* @PrimaryKey("addressID")
* public interface Address extends Storable {
* int getAddressID();
*
* ...
* }
*
* @PrimaryKey("userID")
* public interface UserInfo extends Storable {
* int getUserID();
*
* int getAddressID();
*
* void setAddressID(int value);
*
* // Natural join, which works because Address has a primary key
* // property of addressID which matches a property in this type.
* <b>@Join</b>
* Address getAddress() throws FetchException;
*
* // Explicit join, equivalent to getAddress.
* <b>@Join(internal="addressID", external="addressID")</b>
* Address getCurrentAddress() throws FetchException;
*
* @Nullable
* Integer getParentID();
*
* void setParentID(Integer value);
*
* // Many-to-one relationship
* @Nullable
* <b>@Join(internal="parentID", external="userID")</b>
* UserInfo getParent() throws FetchException;
*
* // One-to-many relationship
* <b>@Join(internal="userID", external="parentID")</b>
* Query<UserInfo> getChildren() throws FetchException;
*
* ...
* }
* </pre>
*
* @author Brian S O'Neill
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface Join {
/**
* List of property names defined in this property's enclosing class or
* interface.
*/
String[] internal() default {};
/**
* List of property names defined in the foreign property's enclosing class
* or interface.
*/
String[] external() default {};
}
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