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/*
 * Copyright (c) 1998, 2024 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:
//     Andrei Ilitchev (Oracle), March 7, 2008
//        - New file introduced for bug 211300.
package org.eclipse.persistence.annotations;

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

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Annotation for {@linkplain org.eclipse.persistence.mappings.TransformationMapping}.
 * Unless the {@linkplain org.eclipse.persistence.mappings.TransformationMapping} is write-only, it should have a
 * {@linkplain ReadTransformer} defining transformation of database column(s) value(s) into attribute value.
 * 
 * Also, unless it's a read-only mapping, either {@linkplain WriteTransformer} or
 * {@linkplain WriteTransformers} annotation should be specified. Each {@linkplain WriteTransformer}
 * defines transformation of the attribute value to a single database column
 * value (column is specified in the {@linkplain WriteTransformer}).
 * 

 * Transformation can be specified within an Entity, MappedSuperclass
 * and Embeddable class.
 *
 * @see Transformation
 * @see WriteTransformer
 * @see WriteTransformers
 * @author Andrei Ilitchev
 */
@Target({METHOD, FIELD})
@Retention(RUNTIME)
public @interface ReadTransformer {
    /**
     * User-defined class that must implement the
     * {@linkplain org.eclipse.persistence.mappings.transformers.AttributeTransformer}
     * interface. The class will be instantiated, its
     * {@linkplain org.eclipse.persistence.mappings.transformers.AttributeTransformer#buildAttributeValue(org.eclipse.persistence.sessions.DataRecord, Object, org.eclipse.persistence.sessions.Session) buildAttributeValue}
     * will be used to create the value to be assigned to the attribute.
     * 

     * Either transformerClass or {@linkplain #method()} must be specified, but not both.
     */
    Class transformerClass() default void.class;

    /**
     * The mapped class must have a method with this name which returns a value
     * to be assigned to the attribute (not assigns the value to the attribute).
     * 
     * Either {@linkplain #transformerClass()} or method must be specified, but not both.
     */
    String method() default "";
}