Cursor paging

Use cursor paging.

Explore further

For detailed documentation that includes this code sample, see the following:

• Datastore Queries

Code sample

C#

To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries. For more information, see the Datastore mode C# API reference documentation.

To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

Query query = new Query("Task")
{
    Limit = pageSize,
};
if (!string.IsNullOrEmpty(pageCursor))
    query.StartCursor = ByteString.FromBase64(pageCursor);

return _db.RunQuery(query).EndCursor?.ToBase64();

Go

To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries. For more information, see the Datastore mode Go API reference documentation.

To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

// cursorStr is a cursor to start querying at.
cursorStr := ""

const pageSize = 5
query := datastore.NewQuery("Tasks").Limit(pageSize)
if cursorStr != "" {
	cursor, err := datastore.DecodeCursor(cursorStr)
	if err != nil {
		log.Fatalf("Bad cursor %q: %v", cursorStr, err)
	}
	query = query.Start(cursor)
}

// Read the tasks.
var tasks []Task
var task Task
it := client.Run(ctx, query)
_, err := it.Next(&task)
for err == nil {
	tasks = append(tasks, task)
	_, err = it.Next(&task)
}
if err != iterator.Done {
	log.Fatalf("Failed fetching results: %v", err)
}

// Get the cursor for the next page of results.
// nextCursor.String can be used as the next page's token.
nextCursor, err := it.Cursor()

Java

To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries. For more information, see the Datastore mode Java API reference documentation.

To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

EntityQuery.Builder queryBuilder =
    Query.newEntityQueryBuilder().setKind("Task").setLimit(pageSize);
if (pageCursor != null) {
  queryBuilder.setStartCursor(pageCursor);
}
QueryResults<Entity> tasks = datastore.run(queryBuilder.build());
while (tasks.hasNext()) {
  Entity task = tasks.next();
  // do something with the task
}
Cursor nextPageCursor = tasks.getCursorAfter();

Node.js

To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries. For more information, see the Datastore mode Node.js API reference documentation.

To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

// By default, google-cloud-node will automatically paginate through all of
// the results that match a query. However, this sample implements manual
// pagination using limits and cursor tokens.
async function runPageQuery(pageCursor) {
  let query = datastore.createQuery('Task').limit(pageSize);

  if (pageCursor) {
    query = query.start(pageCursor);
  }
  const results = await datastore.runQuery(query);
  const entities = results[0];
  const info = results[1];

  if (info.moreResults !== Datastore.NO_MORE_RESULTS) {
    // If there are more results to retrieve, the end cursor is
    // automatically set on `info`. To get this value directly, access
    // the `endCursor` property.
    const results = await runPageQuery(info.endCursor);

    // Concatenate entities
    results[0] = entities.concat(results[0]);
    return results;
  }

  return [entities, info];
}

PHP

To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries. For more information, see the Datastore mode PHP API reference documentation.

To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

/**
 * Fetch a query cursor.
 *
 * @param DatastoreClient $datastore
 * @param int $pageSize
 * @param string $pageCursor
 */
function cursor_paging(DatastoreClient $datastore, int $pageSize, string $pageCursor = '')
{
    $query = $datastore->query()
        ->kind('Task')
        ->limit($pageSize)
        ->start($pageCursor);
    $result = $datastore->runQuery($query);
    $nextPageCursor = '';
    $entities = [];
    /* @var Entity $entity */
    foreach ($result as $entity) {
        $nextPageCursor = $entity->cursor();
        $entities[] = $entity;
    }

    printf('Found %s entities', count($entities));

    $entities = [];
    if (!empty($nextPageCursor)) {
        $query = $datastore->query()
          ->kind('Task')
          ->limit($pageSize)
          ->start($nextPageCursor);
        $result = $datastore->runQuery($query);

        foreach ($result as $entity) {
            $entities[] = $entity;
        }

        printf('Found %s entities with next page cursor', count($entities));
    }
}

Python

To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries. For more information, see the Datastore mode Python API reference documentation.

To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

from google.cloud import datastore

# For help authenticating your client, visit
# https://cloud.google.com/docs/authentication/getting-started
client = datastore.Client()


def get_one_page_of_tasks(cursor=None):
    query = client.query(kind="Task")
    query_iter = query.fetch(start_cursor=cursor, limit=5)
    page = next(query_iter.pages)

    tasks = list(page)
    next_cursor = query_iter.next_page_token

    return tasks, next_cursor

Ruby

To learn how to install and use the client library for Datastore mode, see Datastore mode client libraries. For more information, see the Datastore mode Ruby API reference documentation.

To authenticate to Datastore mode, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

page_size = 2
query = datastore.query("Task")
                 .limit(page_size)
tasks = datastore.run query

page_cursor = tasks.cursor

query = datastore.query("Task")
                 .limit(page_size)
                 .start(page_cursor)

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