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The AWS Java SDK for Amazon DynamoDB module holds the client classes that are used for communicating with Amazon DynamoDB Service
/*
* Copyright 2010-2024 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.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. 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 java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.zip.Adler32;
import com.amazonaws.annotation.SdkInternalApi;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
/**
* This class will contain logic for converting an update object that customer has passed-in into
* low level update expression and corresponding expression attribute maps.
* Currently this entails generating a string that can be used as a substitution token in the
* updateExpression and insert corresponding attribute name/value in the expressionAttributeNameMap/expressionAttributeValueMap
*
* For ex: Attribute will be converted to:
* updateExpression = "SET #5d810=:5d810" and
* expressionAttributeNameMap = {{#5d810, "stringAttribute"},...}
* expressionAttributeValueMap = {{:5d810, {S: "sdkAttributeStringValue"}},...}
*
* Null valued attributes will be converted to REMOVE expressions similarly and appended to the updateExpression
*
* We use deterministic token generation logic to ensure request contents remain same across retried transactionWrite calls.
* This will help in ensuring idempotency across retried calls.
* Read more on idempotency of transactionWrite API here:
* https://docs.aws.amazon.com/en_us/amazondynamodb/latest/APIReference/API_TransactWriteItems.html#DDB-TransactWriteItems-request-ClientRequestToken
*/
@SdkInternalApi
public class UpdateExpressionGenerator {
/**
* Generate a string that can be used as a substitution token for attributeNames and attributeValues in
* update expression. De-dupes generated string on existingAttributesKeyList.
* The string starts with a baseToken's substring that is passed in from the caller and then appended with a hex string
* the hex string represents the locally incremented counter across attributes.
* In case there is a conflict with above generated string, we'll instead substitute with the full baseToken
* instead of the baseToken substring
*
* For ex:
* For a baseToken: 5d81, suffixCounter: 9
* the *next* generated string will be 5d81a, 5d81 from baseToken and `a` from the incremented hex counter 9 -> a
*/
private String generateSubstitutionTokenString(String baseToken,
Long suffixCounter,
Set expressionAttributeNamesKeys,
Set expressionAttributeValuesKeys) {
String hexSuffix = Long.toHexString(suffixCounter);
String tokenBase = baseToken.substring(0, Math.min(baseToken.length(), 4)) + hexSuffix;
if (!expressionAttributeNamesKeys.contains(getExpressionAttributeNameSubstitutionToken(tokenBase)) &&
!expressionAttributeValuesKeys.contains(getExpressionAttributeValueSubstitutionToken(tokenBase))) {
return tokenBase;
}
// Fallback to fullToken in case of conflict
String fullToken = baseToken + hexSuffix;
if (!expressionAttributeNamesKeys.contains(getExpressionAttributeNameSubstitutionToken(fullToken)) &&
!expressionAttributeValuesKeys.contains(getExpressionAttributeValueSubstitutionToken(fullToken))) {
return fullToken;
} else {
throw new DynamoDBMappingException("Failed to process update operation inside transactionWrite request due to conflict with expressionAttributeName or expressionAttributeValue token name: "
+ fullToken + ". Please replace this token name with a different token name.");
}
}
private String generateSubstitutionTokenString(String baseToken,
Long suffixCounter,
Set expressionAttributeNamesKeys) {
return generateSubstitutionTokenString(baseToken,
suffixCounter,
expressionAttributeNamesKeys,
Collections.emptySet());
}
/**
* Merge nonKeyAttributes along with any condition expression attributes and generate corresponding update expression
*/
public String generateUpdateExpressionAndUpdateAttributeMaps(Map expressionAttributeNamesMap,
Map expressionsAttributeValuesMap,
Map nonKeyNonNullAttributeValueMap,
List nullValuedNonKeyAttributeNames) {
StringBuilder updateExpressionSetBuilder = new StringBuilder();
StringBuilder updateExpressionDeleteBuilder = new StringBuilder();
// This has to be a sorted list to ensure deterministic retrieval order for nonKeyNonNullAttributes
// while auto generating update expression tokens
List sortedNonKeyNonNullAttributeNames = new ArrayList(nonKeyNonNullAttributeValueMap.keySet());
Collections.sort(sortedNonKeyNonNullAttributeNames);
// Sort the null valued non-key attributes to ensure deterministic retrieval order for nullValuedNonKeyAttributes
// while auto generating update expression tokens
List sortedNullValuedNonKeyAttributeNames = new ArrayList(nullValuedNonKeyAttributeNames);
Collections.sort(sortedNullValuedNonKeyAttributeNames);
// Initialize baseToken and suffixCounter for each update item
String baseToken = getBaseToken(sortedNonKeyNonNullAttributeNames, sortedNullValuedNonKeyAttributeNames);
Long suffixCounter = 0L;
if (sortedNonKeyNonNullAttributeNames.size() > 0) {
updateExpressionSetBuilder.append("SET ");
List updateStringSetExpressions = new ArrayList();
for (String nonKeyAttributeName : sortedNonKeyNonNullAttributeNames) {
String tokenBase = generateSubstitutionTokenString(baseToken,
suffixCounter,
expressionAttributeNamesMap.keySet(),
expressionsAttributeValuesMap.keySet());
suffixCounter++;
String tokenKeyName = getExpressionAttributeNameSubstitutionToken(tokenBase);
String tokenValueName = getExpressionAttributeValueSubstitutionToken(tokenBase);
expressionAttributeNamesMap.put(tokenKeyName, nonKeyAttributeName);
expressionsAttributeValuesMap.put(tokenValueName, nonKeyNonNullAttributeValueMap.get(nonKeyAttributeName));
updateStringSetExpressions.add(tokenKeyName + " = " + tokenValueName);
}
for (int i = 0; i < updateStringSetExpressions.size() - 1; i++) {
updateExpressionSetBuilder.append(updateStringSetExpressions.get(i) + ", ");
}
updateExpressionSetBuilder.append(updateStringSetExpressions.get(updateStringSetExpressions.size() - 1));
}
if (sortedNullValuedNonKeyAttributeNames.size() > 0) {
updateExpressionDeleteBuilder.append("REMOVE ");
List updateStringDeleteExpressions = new ArrayList();
for (String nullAttributeName : sortedNullValuedNonKeyAttributeNames) {
String tokenBaseString = generateSubstitutionTokenString(baseToken,
suffixCounter,
expressionAttributeNamesMap.keySet());
suffixCounter++;
String tokenKeyName = getExpressionAttributeNameSubstitutionToken(tokenBaseString);
expressionAttributeNamesMap.put(tokenKeyName, nullAttributeName);
updateStringDeleteExpressions.add(tokenKeyName);
}
for (int i = 0; i < updateStringDeleteExpressions.size() - 1; i++) {
updateExpressionDeleteBuilder.append(updateStringDeleteExpressions.get(i) + ", ");
}
updateExpressionDeleteBuilder.append(updateStringDeleteExpressions.get(updateStringDeleteExpressions.size() - 1));
}
StringBuilder updateExpression = new StringBuilder();
if (updateExpressionSetBuilder.length() > 0) {
updateExpression.append(updateExpressionSetBuilder.toString());
}
if (updateExpressionDeleteBuilder.length() > 0) {
updateExpression.append(" " + updateExpressionDeleteBuilder.toString());
}
return updateExpression.toString();
}
private static String getExpressionAttributeNameSubstitutionToken(String tokenBase) {
return "#" + tokenBase;
}
private static String getExpressionAttributeValueSubstitutionToken(String tokenBase) {
return ":" + tokenBase;
}
/**
* Uses attribute names from sortedNonKeyNonNullAttributeNames and sortedNullValuedNonKeyAttributeNames to generate an {@link Adler32} checkSum
* Adler32 generates checksum that is unique enough to be used as a token within an update item and faster to compute than CRC32.
*/
private String getBaseToken(List sortedNonKeyNonNullAttributeNames,
List sortedNullValuedNonKeyAttributeNames) {
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
DataOutputStream dataOutputStream = new DataOutputStream(byteArrayOutputStream);
try {
for (String nonKeyNonNullAttributeName : sortedNonKeyNonNullAttributeNames) {
dataOutputStream.writeUTF(nonKeyNonNullAttributeName);
}
for (String nullValuedNonKeyAttributeName : sortedNullValuedNonKeyAttributeNames) {
dataOutputStream.writeUTF(nullValuedNonKeyAttributeName);
}
} catch (IOException e) {
throw new DynamoDBMappingException("Failed to process update operation inside transactionWrite request due to an IOException ", e);
}
Adler32 adler32 = new Adler32();
adler32.update(byteArrayOutputStream.toByteArray());
return Long.toHexString(adler32.getValue());
}
}