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/*
 * Copyright (c) 2011, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Matt MacIvor = 2.1 - Initial contribution
package org.eclipse.persistence.oxm.annotations;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * XPath based mapping is what allows an existing object model to be mapped
 * to an existing XML schema.  The {@code @XmlPath} annotation is the means by
 * which XPath based mapping is achieved.
 * Example 1 - Using {@code @XmlPath} to Add a Grouping Element
 * Sometimes grouping elements are added to your document to organise data.
 * JAXB has this concept for collection properties in the form of
 * {@code @XmlElementWrapper}.  Here we'll use {@code @XmlPath} for
 * non-collection properties. In this case we'll nest the billing/shipping
 * address data within the "contact-info" element.
 *  * import javax.xml.bind.annotation.*;
 * import org.eclipse.persistence.oxm.annotations.XmlPath;
 *
 * @XmlRootElement
 * @XmlAccessorType(XmlAccessType.FIELD)
 * public class Customer {
 *     @XmlPath("contact-info/billing-address")
 *     private Address billingAddress;
 *
 *     @XmlPath("contact-info/shipping-address")
 *     private Address shippingAddress;
 * }
 * 
 * This will produce XML like:
 * {@code
 * 
 * <customer>
 *     <contact-info>
 *         <billing-address>
 *             <street>1 Billing Street</street>
 *         </billing-address>
 *         <shipping-address>
 *             <street>2 Shipping Road</street>
 *         </shipping-address>
 *     </contact-info>
 * </customer>
 * }
 * 
 * Example 2 - Using {@code @XmlPath} to Map by Position
 * Normally in JAXB elements with the same name must be mapped to a
 * collection property.  Using the @XmlPath extension you map non-collection
 * properties to a repeated element by index.
 *  * import javax.xml.bind.annotation.*;
 * import org.eclipse.persistence.oxm.annotations.XmlPath;
 *
 * @XmlRootElement
 * @XmlAccessorType(XmlAccessType.FIELD)
 * public class Customer {
 *     @XmlPath("address[1]")
 *     private Address billingAddress;
 *
 *     @XmlPath("address[2]")
 *     private Address shippingAddress;
 * }
 * 
 * This will produce XML like:
 * {@code
 * 
 * <customer>
 *     <address>
 *         <street>1 Billing Street</street>
 *     </address>
 *     <address>
 *         <street>2 Shipping Road</street>
 *     </address>
 * </customer>
 * }
 * 
 * Example 3 - Using {@code @XmlPath} to Map Two Objects to the Same Node
 * We have seen how {@code @XmlPath} can be used to expand the structure by
 * adding a grouping element. {@code @XmlPath} can also be used to collapse the
 * structure by mapping two objects to the same node.
 *  * import javax.xml.bind.annotation.*;
 * import org.eclipse.persistence.oxm.annotations.XmlPath;
 *
 * @XmlRootElement @XmlAccessorType(XmlAccessType.FIELD)
 * public class Customer {
 *     @XmlPath(".")
 *     private Address billingAddress;
 *
 *     private Address shippingAddress;
 * }
 * 
 * This will produce XML like:
 * {@code
 * 
 * <customer>
 *     <street>1 Billing Street</street>
 *     <shippingAddress>
 *         <street>2 Shipping Road</street>
 *     </shippingAddress>
 * </customer>
 * }
 * 
 */
@Target({ElementType.FIELD, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface XmlPath {

    /**
     * The XPath for this property.  A subset of the XPath specification may be
     * used to specify mappings.  The following concepts are supported:
     * 
     * Attribute - "@id"
     * Element - "address"
     * Element by Position - "address[1]"
     * Element by Predicate - "address[@type='mailing']"
     * Element Text - "name/text()"
     * Text - "text()"
     * Self - "."
     * Combination - "personal-info/name[2]/text()"
     * 
     * For namespace qualified nodes, the prefixes defined in the XmlNs
     * annotations can be used to qualify the XPath fragments.  Unqualified
     * fragments will assumed to be in the namespace specified using
     * @XmlSchema.
     * Example
     * Assuming the following namespace information has been set up using the
     * @XmlSchema annotation:
     *      * @XmlSchema(namespace = "http://www.example.org/FOO",
     *            xmlns = {@XmlNs(prefix="ns", namespaceURI="http://www.example.com/BAR")},
     *            elementFormDefault = XmlNsForm.QUALIFIED)
     * package org.example;
     *
     * import javax.xml.bind.annotation.*;
     * 
     * Then the following XPath:
     *      * @XmlPath("contact-info/ns:address/@id")
     * 
     * Will be qualified as:
     * 
     * contact-info - in "http://www.example.org/FOO" namespace.
     * address - in "http://www.example.com/BAR" namespace.
     * @id - in no namespace.
     * 
     * @see javax.xml.bind.annotation.XmlSchema
     * @see javax.xml.bind.annotation.XmlNs
     */
    String value();

}