com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBVersionAttribute Maven / Gradle / Ivy
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/*
* Copyright 2011-2016 Amazon.com, 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://aws.amazon.com/apache2.0
*
* This file 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.amazonaws.services.dynamodbv2.datamodeling;
import com.amazonaws.services.dynamodbv2.datamodeling.StandardTypeConverters.Scalar;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.math.BigInteger;
import java.util.Arrays;
/**
* Annotation for marking a property as an optimistic locking version attribute.
* Applied to the getter method or the class field for the class's version
* property. If the annotation is applied directly to the class field, the
* corresponding getter and setter must be declared in the same class.
*
* Only nullable, integral numeric types (e.g. Integer, Long) can be used as
* version properties. On a save() operation, the {@link DynamoDBMapper} will
* attempt to increment the version property and assert that the service's value
* matches the client's. New objects will be assigned a version of 1 when saved.
*
* Note that for batchWrite, and by extension batchSave and batchDelete, no
* version checks are performed, as required by the
* {@link com.amazonaws.services.dynamodbv2.AmazonDynamoDB#batchWriteItem(BatchWriteItemRequest)}
* API.
*/
@DynamoDB
@DynamoDBAutoGenerated(generator=DynamoDBVersionAttribute.Generator.class)
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
public @interface DynamoDBVersionAttribute {
/**
* Optional parameter when the name of the attribute as stored in DynamoDB
* should differ from the name used by the getter / setter.
*/
String attributeName() default "";
/**
* Version auto-generator.
*/
static final class Generator implements DynamoDBAutoGenerator {
private final Sequence sequence;
public Generator(final Class targetType, final DynamoDBVersionAttribute annotation) {
this.sequence = Sequences.of(targetType);
}
@Override
public final DynamoDBAutoGenerateStrategy getGenerateStrategy() {
return DynamoDBAutoGenerateStrategy.ALWAYS;
}
@Override
public final T generate(final T currentValue) {
return sequence.next(currentValue);
}
static interface Sequence {
public T next(final T o);
}
private static enum Sequences {
BIG_INTEGER(Scalar.BIG_INTEGER, new Sequence() {
public final BigInteger next(final BigInteger o) {
return o == null ? BigInteger.ONE : o.add(BigInteger.ONE);
}
}),
BYTE(Scalar.BYTE, new Sequence() {
public final Byte next(final Byte o) {
return o == null ? Byte.valueOf((byte)1) : (byte)((o + 1) % Byte.MAX_VALUE);
}
}),
INTEGER(Scalar.INTEGER, new Sequence() {
public final Integer next(final Integer o) {
return o == null ? Integer.valueOf(1) : o + 1;
}
}),
LONG(Scalar.LONG, new Sequence() {
public final Long next(final Long o) {
return o == null ? Long.valueOf(1L) : o + 1L;
}
}),
SHORT(Scalar.SHORT, new Sequence() {
public final Short next(final Short o) {
return o == null ? Short.valueOf((short)1) : (short)(o + 1);
}
});
private final Sequence sequence;
private final Scalar scalar;
private Sequences(final Scalar scalar, final Sequence sequence) {
this.sequence = sequence;
this.scalar = scalar;
}
private static final Sequence of(final Class targetType) {
final Scalar target = Scalar.of(targetType);
for (final Sequences s : Sequences.values()) {
if (s.scalar == target) {
return (Sequence)s.sequence;
}
}
return new Sequence() { //<- for backwards compatibility
public T next(final T o) {
throw new DynamoDBMappingException("type [" + targetType + "] is not supported" +
"; only " + Arrays.toString(Sequences.values()) + " allowed");
}
};
}
}
}
}