#DynamoDB #JavaSDK #AWS

dynamodb.java

private Result getPeopleByGSI(@NotNull final String indexedReference, final String... attributes) {
        // make reference the index 
        final DynamoDbIndex<People> index = DynamoUtil.peopleTable.index("someIndexedAttribute-index");
        // Apply value to the indexed attribute (as the PartitionKey)
        final QueryConditional queryConditional = QueryConditional.keyEqualTo(
                Key.builder().partitionValue(indexedReference).build());

        // Compose Filter expressions
        final List<String> expressions = new ArrayList<>();
        final Expression.Builder expressionBuilder = Expression.builder();

        // Build other 
        if (attributes[0] != null) {
            expressions.add("contains(#attribute1, :attribute1)");
            expressionBuilder.putExpressionName("#attribute1", "attribute1");
            expressionBuilder.putExpressionValue(":attribute1", AttributeValue.builder()
                    .s(type.name()).build());
        }
        // etc...
        if (attribute[n] != null) {
            expressions.add("#attributeN = :attributeN");
            expressionBuilder.putExpressionName("#attributeN", "attributeN");
            expressionBuilder.putExpressionValue(":attributeN", AttributeValue.builder()
                    .s(primary).build());
        }
        expressionBuilder.expression(String.join(" AND ", expressions));

        final QueryEnhancedRequest.Builder requestBuilder = QueryEnhancedRequest.builder()
                .queryConditional(queryConditional)
                .consistentRead(false); // ⚠️ ConsistentRead is _not_ supported on queries with GSIs
        final QueryEnhancedRequest request;
        if (expressions.isEmpty()) {
            // ⚠️ Empty Filter-Expressions are not allowed!
            request = requestBuilder.build();
        } else {
            request = requestBuilder.filterExpression(expressionBuilder.build())
            .build();
        }
        // Run the query
        final SdkIterable<Page<People>> pagesInterable = index.query(request);
        // map the pages to items
        // ⚠️ Pages returned my be empty
        final List<People> people = pagesInterable.stream()
                .map(Page::items)
                .flatMap(Collection::stream)
                .collect(Collectors.toList());
        
        return Response.ok(people).build();
    }