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/*
* Copyright 2013-2016 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.mobileconnectors.dynamodbv2.dynamodbmapper;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import java.util.Map;
/**
* A hook allowing a custom transform/untransform of the raw attribute values
* immediately before writing them into DynamoDB and immediately after reading
* them out of DynamoDB, but with extra context about the model class not
* available at the raw AmazonDymnamoDB level.
*
* This interface contains both a {@code transform} method and a corresponding
* {@code untransform} method. These methods SHOULD be inverses, such that
* untransform(transform(value)) == value.
*/
public interface AttributeTransformer {
/**
* Parameters for the {@code transform} and {@code untransform} methods, so
* we don't have to break the interface in order to add additional
* parameters.
*
* Consuming code should NOT implement this interface.
*/
interface Parameters {
/**
* Returns the raw attribute values to be transformed or untransformed.
* The returned map is not modifiable.
*
* @return the raw attribute values to transform or untransform
*/
Map getAttributeValues();
/**
* Returns true if this transformation is being called as part of a
* partial update operation. If true, the attributes returned by
* {@link #getAttributeValues()} do not represent the entire new item,
* but only a snapshot of the attributes which are getting new values.
*
* Implementations which do not support transforming a partial view of
* an item (for example, because they need to calculate a signature
* based on all of the item's attributes that won't be valid if only a
* subset of the attributes are taken into consideration) should check
* this flag and throw an exception rather than than corrupting the data
* in DynamoDB.
*
* This method always returns {@code false} for instances passed to
* {@link AttributeTransformer#untransform(Parameters)}.
*
* @return true if this operation is a partial update, false otherwise
*/
boolean isPartialUpdate();
/**
* @return the type of the model class we're transforming to or from
*/
Class getModelClass();
/**
* @return the mapper config for this operation
*/
DynamoDBMapperConfig getMapperConfig();
/**
* @return the name of the DynamoDB table the attributes were read from
* or will be written to
*/
String getTableName();
/**
* @return the name of the hash key for the table
*/
String getHashKeyName();
/**
* @return the name of the range key for the table, if it has one,
* otherwise {@code null}
*/
String getRangeKeyName();
}
/**
* Transforms the input set of attribute values derived from the model
* object before writing them into DynamoDB.
*
* @param parameters transformation parameters
* @return the transformed attribute value map
*/
Map transform(Parameters parameters);
/**
* Untransform the input set of attribute values read from DynamoDB before
* creating a model object from them.
*
* @param parameters transformation parameters
* @return the untransformed attribute value map
*/
Map untransform(Parameters parameters);
}