Multi tool use

Clash Royale CLAN TAG

Querying DynamoDB GSI with a list of values

I have a table of "team memberships" with primary partition key of "team_id" , a primary sort key of "email" and a GSI with "email" as partition key.

Given a list of emails I would like to find all the memberships for all the emails in the list in the most efficient way possible.

I know that for a single email I can do the following:

Membership membership = new Membership();
membership.setEmail(email.toLowerCase());

DynamoDBQueryExpression<Membership> expression = new DynamoDBQueryExpression<Membership>()
.withHashKeyValues(membership)
.withIndexName(EMAIL_INDEX)
.withConsistentRead(false);

return mapper.query(Membership.class, expression);


which returns a list of memberships for the given email.

(So for my list of emails, I could do the above for each email in the list, but I would like to know if it is possible to do in one step).

I would like to be able to do something like:

List<Membership> memberships = allEmails.stream().map(email -> {
Membership m = new Membership();
m.setEmail(email.toLowerCase());
return m;
}).collect(Collectors.toList());

DynamoDBQueryExpression<Membership> expression = new DynamoDBQueryExpression<Membership>()
.withHashKeyValues(memberships) // <--- passing a list
.withIndexName(EMAIL_INDEX)
.withConsistentRead(false);


which clearly doesn't work.

What are the alternatives?

1 Answer
1

Batch get item api can be used to get multiple partition keys from either main table or GSI.

Batch get item java

try {

TableKeysAndAttributes forumTableKeysAndAttributes = new TableKeysAndAttributes(forumTableName);
// Add a partition key
forumTableKeysAndAttributes.addHashOnlyPrimaryKeys("Name", "Amazon S3", "Amazon DynamoDB");

TableKeysAndAttributes threadTableKeysAndAttributes = new TableKeysAndAttributes(threadTableName);
// Add a partition key and a sort key
threadTableKeysAndAttributes.addHashAndRangePrimaryKeys("ForumName", "Subject", "Amazon DynamoDB",
"DynamoDB Thread 1", "Amazon DynamoDB", "DynamoDB Thread 2", "Amazon S3", "S3 Thread 1");

System.out.println("Making the request.");

BatchGetItemOutcome outcome = dynamoDB.batchGetItem(forumTableKeysAndAttributes,
threadTableKeysAndAttributes);

Map<String, KeysAndAttributes> unprocessed = null;

do {
for (String tableName : outcome.getTableItems().keySet()) {
System.out.println("Items in table " + tableName);
List<Item> items = outcome.getTableItems().get(tableName);
for (Item item : items) {
System.out.println(item.toJSONPretty());
}
}

// Check for unprocessed keys which could happen if you exceed
// provisioned
// throughput or reach the limit on response size.
unprocessed = outcome.getUnprocessedKeys();

if (unprocessed.isEmpty()) {
System.out.println("No unprocessed keys found");
}
else {
System.out.println("Retrieving the unprocessed keys");
outcome = dynamoDB.batchGetItemUnprocessed(unprocessed);
}

} while (!unprocessed.isEmpty());

}
catch (Exception e) {
System.err.println("Failed to retrieve items.");
System.err.println(e.getMessage());
}


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