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DDB Enhanced: Added support for projection expression
added new property attributesToProject to QueryEnhancedRequest and ScanEnhancedRequest which enables to fetch only partial results to save the bandwidth of the queries.
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‎CHANGELOG.md

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@@ -1,3 +1,9 @@
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# __2.11.10__
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## __Amazon DynamoDB Enhanced Client [Preview]__
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- ### Features
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- The enhanced DDB query and scan request now supports projections.
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# __2.11.9__ __2020-04-03__
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## __AWS RoboMaker__
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- ### Features

‎services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/internal/operations/QueryOperation.java

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@@ -15,8 +15,14 @@
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package software.amazon.awssdk.enhanced.dynamodb.internal.operations;
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import static software.amazon.awssdk.enhanced.dynamodb.internal.EnhancedClientUtils.cleanAttributeName;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.function.Function;
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import java.util.function.UnaryOperator;
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import software.amazon.awssdk.annotations.SdkInternalApi;
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import software.amazon.awssdk.core.async.SdkPublisher;
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import software.amazon.awssdk.core.pagination.sync.SdkIterable;
@@ -37,6 +43,8 @@
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public class QueryOperation<T> implements PaginatedTableOperation<T, QueryRequest, QueryResponse>,
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PaginatedIndexOperation<T, QueryRequest, QueryResponse> {
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private static final UnaryOperator<String> PROJECTION_EXPRESSION_KEY_MAPPER = k -> "#AMZN_MAPPED_" + cleanAttributeName(k);
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private final QueryEnhancedRequest request;
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private QueryOperation(QueryEnhancedRequest request) {
@@ -60,6 +68,19 @@ public QueryRequest generateRequest(TableSchema<T> tableSchema,
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expressionNames = Expression.joinNames(expressionNames, this.request.filterExpression().expressionNames());
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}
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String projectionExpression = null;
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if (this.request.attributesToProject() != null) {
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List<String> placeholders = new ArrayList<>();
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Map<String, String> projectionPlaceholders = new HashMap<>();
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this.request.attributesToProject().forEach(attr -> {
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String placeholder = PROJECTION_EXPRESSION_KEY_MAPPER.apply(attr);
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placeholders.add(placeholder);
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projectionPlaceholders.put(placeholder, attr);
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});
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projectionExpression = String.join(",", placeholders);
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expressionNames = Expression.joinNames(expressionNames, projectionPlaceholders);
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}
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QueryRequest.Builder queryRequest = QueryRequest.builder()
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.tableName(operationContext.tableName())
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.keyConditionExpression(queryExpression.expression())
@@ -68,7 +89,8 @@ public QueryRequest generateRequest(TableSchema<T> tableSchema,
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.scanIndexForward(this.request.scanIndexForward())
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.limit(this.request.limit())
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.exclusiveStartKey(this.request.exclusiveStartKey())
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.consistentRead(this.request.consistentRead());
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.consistentRead(this.request.consistentRead())
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.projectionExpression(projectionExpression);
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if (!TableMetadata.primaryIndexName().equals(operationContext.indexName())) {
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queryRequest = queryRequest.indexName(operationContext.indexName());

‎services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/internal/operations/ScanOperation.java

+37-4
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@@ -15,25 +15,36 @@
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package software.amazon.awssdk.enhanced.dynamodb.internal.operations;
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import static software.amazon.awssdk.enhanced.dynamodb.internal.EnhancedClientUtils.cleanAttributeName;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.function.Function;
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import java.util.function.UnaryOperator;
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import software.amazon.awssdk.annotations.SdkInternalApi;
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import software.amazon.awssdk.core.async.SdkPublisher;
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import software.amazon.awssdk.core.pagination.sync.SdkIterable;
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import software.amazon.awssdk.enhanced.dynamodb.DynamoDbEnhancedClientExtension;
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import software.amazon.awssdk.enhanced.dynamodb.Expression;
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import software.amazon.awssdk.enhanced.dynamodb.TableMetadata;
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import software.amazon.awssdk.enhanced.dynamodb.TableSchema;
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import software.amazon.awssdk.enhanced.dynamodb.internal.EnhancedClientUtils;
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import software.amazon.awssdk.enhanced.dynamodb.model.Page;
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import software.amazon.awssdk.enhanced.dynamodb.model.ScanEnhancedRequest;
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import software.amazon.awssdk.services.dynamodb.DynamoDbAsyncClient;
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import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
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import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
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import software.amazon.awssdk.services.dynamodb.model.ScanRequest;
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import software.amazon.awssdk.services.dynamodb.model.ScanResponse;
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@SdkInternalApi
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public class ScanOperation<T> implements PaginatedTableOperation<T, ScanRequest, ScanResponse>,
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PaginatedIndexOperation<T, ScanRequest, ScanResponse> {
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private static final UnaryOperator<String> PROJECTION_EXPRESSION_KEY_MAPPER = k -> "#AMZN_MAPPED_" + cleanAttributeName(k);
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private final ScanEnhancedRequest request;
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private ScanOperation(ScanEnhancedRequest request) {
@@ -48,20 +59,42 @@ public static <T> ScanOperation<T> create(ScanEnhancedRequest request) {
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public ScanRequest generateRequest(TableSchema<T> tableSchema,
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OperationContext operationContext,
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DynamoDbEnhancedClientExtension extension) {
62+
Map<String, AttributeValue> expressionValues = null;
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Map<String, String> expressionNames = null;
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if (this.request.filterExpression() != null) {
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expressionValues = this.request.filterExpression().expressionValues();
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expressionNames = this.request.filterExpression().expressionNames();
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}
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70+
String projectionExpression = null;
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if (this.request.attributesToProject() != null) {
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List<String> placeholders = new ArrayList<>();
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Map<String, String> projectionPlaceholders = new HashMap<>();
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this.request.attributesToProject().forEach(attr -> {
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String placeholder = PROJECTION_EXPRESSION_KEY_MAPPER.apply(attr);
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placeholders.add(placeholder);
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projectionPlaceholders.put(placeholder, attr);
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});
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projectionExpression = String.join(",", placeholders);
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expressionNames = Expression.joinNames(expressionNames, projectionPlaceholders);
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}
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ScanRequest.Builder scanRequest = ScanRequest.builder()
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.tableName(operationContext.tableName())
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.limit(this.request.limit())
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.exclusiveStartKey(this.request.exclusiveStartKey())
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.consistentRead(this.request.consistentRead());
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.consistentRead(this.request.consistentRead())
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.expressionAttributeValues(expressionValues)
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.expressionAttributeNames(expressionNames)
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.projectionExpression(projectionExpression);
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if (!TableMetadata.primaryIndexName().equals(operationContext.indexName())) {
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scanRequest = scanRequest.indexName(operationContext.indexName());
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}
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if (this.request.filterExpression() != null) {
62-
scanRequest = scanRequest.filterExpression(this.request.filterExpression().expression())
63-
.expressionAttributeValues(this.request.filterExpression().expressionValues())
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.expressionAttributeNames(this.request.filterExpression().expressionNames());
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scanRequest = scanRequest.filterExpression(this.request.filterExpression().expression());
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}
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return scanRequest.build();

‎services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/model/QueryEnhancedRequest.java

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package software.amazon.awssdk.enhanced.dynamodb.model;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.Collection;
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import java.util.Collections;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import software.amazon.awssdk.annotations.SdkPublicApi;
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import software.amazon.awssdk.enhanced.dynamodb.DynamoDbAsyncIndex;
@@ -41,6 +46,7 @@ public final class QueryEnhancedRequest {
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private final Integer limit;
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private final Boolean consistentRead;
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private final Expression filterExpression;
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private final List<String> attributesToProject;
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private QueryEnhancedRequest(Builder builder) {
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this.queryConditional = builder.queryConditional;
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this.limit = builder.limit;
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this.consistentRead = builder.consistentRead;
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this.filterExpression = builder.filterExpression;
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this.attributesToProject = builder.attributesToProject != null
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? Collections.unmodifiableList(builder.attributesToProject)
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: null;
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}
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/**
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.scanIndexForward(scanIndexForward)
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.limit(limit)
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.consistentRead(consistentRead)
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.filterExpression(filterExpression);
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.filterExpression(filterExpression)
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.attributesToProject(attributesToProject);
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}
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/**
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return filterExpression;
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}
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/**
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* Returns the list of projected attributes on this request object, or an null if no projection is specified.
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*/
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public List<String> attributesToProject() {
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return attributesToProject;
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}
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@Override
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public boolean equals(Object o) {
118135
if (this == o) {
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142159
if (consistentRead != null ? ! consistentRead.equals(query.consistentRead) : query.consistentRead != null) {
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return false;
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}
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if (attributesToProject != null
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? ! attributesToProject.equals(query.attributesToProject)
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: query.attributesToProject != null
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) {
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return false;
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}
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return filterExpression != null ? filterExpression.equals(query.filterExpression) : query.filterExpression == null;
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}
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@@ -153,6 +176,7 @@ public int hashCode() {
153176
result = 31 * result + (limit != null ? limit.hashCode() : 0);
154177
result = 31 * result + (consistentRead != null ? consistentRead.hashCode() : 0);
155178
result = 31 * result + (filterExpression != null ? filterExpression.hashCode() : 0);
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result = 31 * result + (attributesToProject != null ? attributesToProject.hashCode() : 0);
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return result;
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}
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private Integer limit;
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private Boolean consistentRead;
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private Expression filterExpression;
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private List<String> attributesToProject;
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172197
private Builder() {
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}
@@ -255,6 +280,73 @@ public Builder filterExpression(Expression filterExpression) {
255280
return this;
256281
}
257282

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/**
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* <p>
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* Sets a collection of the attribute names to be retrieved from the database. These attributes can include
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* scalars, sets, or elements of a JSON document.
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* </p>
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* <p>
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* If no attribute names are specified, then all attributes will be returned. If any of the requested attributes
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* are not found, they will not appear in the result.
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* </p>
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* <p>
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* For more information, see <a href=
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* "https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html"
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* >Accessing Item Attributes</a> in the <i>Amazon DynamoDB Developer Guide</i>.
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* </p>
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* @param attributesToProject
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* A collection of the attributes names to be retrieved from the database.
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* @return Returns a reference to this object so that method calls can be chained together.
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*/
301+
public Builder attributesToProject(Collection<String> attributesToProject) {
302+
this.attributesToProject = attributesToProject != null ? new ArrayList<>(attributesToProject) : null;
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return this;
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}
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/**
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* <p>
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* Sets one or more attribute names to be retrieved from the database. These attributes can include
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* scalars, sets, or elements of a JSON document.
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* </p>
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* <p>
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* If no attribute names are specified, then all attributes will be returned. If any of the requested attributes
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* are not found, they will not appear in the result.
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* </p>
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* <p>
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* For more information, see <a href=
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* "https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html"
318+
* >Accessing Item Attributes</a> in the <i>Amazon DynamoDB Developer Guide</i>.
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* </p>
320+
* @param attributesToProject
321+
* One or more attributes names to be retrieved from the database.
322+
* @return Returns a reference to this object so that method calls can be chained together.
323+
*/
324+
public Builder attributesToProject(String... attributesToProject) {
325+
return attributesToProject(Arrays.asList(attributesToProject));
326+
}
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/**
329+
* <p>
330+
* Adds a single attribute name to be retrieved from the database. This attribute can include
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* scalars, sets, or elements of a JSON document.
332+
* </p>
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* <p>
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* For more information, see <a href=
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* "https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.AccessingItemAttributes.html"
336+
* >Accessing Item Attributes</a> in the <i>Amazon DynamoDB Developer Guide</i>.
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* </p>
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* @param attributeToProject
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* An additional single attribute name to be retrieved from the database.
340+
* @return Returns a reference to this object so that method calls can be chained together.
341+
*/
342+
public Builder addAttributeToProject(String attributeToProject) {
343+
if (attributesToProject == null) {
344+
attributesToProject = new ArrayList<>();
345+
}
346+
attributesToProject.add(attributeToProject);
347+
return this;
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}
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258350
public QueryEnhancedRequest build() {
259351
return new QueryEnhancedRequest(this);
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}

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