Read data with index

Read data by using an index.

Documentation pages that include this code sample

To view the code sample used in context, see the following documentation:

Code sample

C#

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.

string connectionString =
$"Data Source=projects/{projectId}/instances/{instanceId}"
+ $"/databases/{databaseId}";
// Create connection to Cloud Spanner.
using (var connection = new SpannerConnection(connectionString))
{
    var cmd = connection.CreateSelectCommand(
        "SELECT AlbumId, AlbumTitle, MarketingBudget FROM Albums@ "
        + "{FORCE_INDEX=AlbumsByAlbumTitle} "
        + $"WHERE AlbumTitle >= @startTitle "
        + $"AND AlbumTitle < @endTitle",
        new SpannerParameterCollection {
            {"startTitle", SpannerDbType.String},
            {"endTitle", SpannerDbType.String} });
    cmd.Parameters["startTitle"].Value = startTitle;
    cmd.Parameters["endTitle"].Value = endTitle;
    using (var reader = await cmd.ExecuteReaderAsync())
    {
        while (await reader.ReadAsync())
        {
            var marketingBudget = reader.IsDBNull(
                reader.GetOrdinal("MarketingBudget")) ?
                "" :
                reader.GetFieldValue<string>("MarketingBudget");
            Console.WriteLine("AlbumId : "
            + reader.GetFieldValue<string>("AlbumId")
            + " AlbumTitle : "
            + reader.GetFieldValue<string>("AlbumTitle")
            + " MarketingBudget : "
            + marketingBudget);
        }
    }
}

C++

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.

void ReadDataWithIndex(google::cloud::spanner::Client client) {
  namespace spanner = ::google::cloud::spanner;

  spanner::ReadOptions read_options;
  read_options.index_name = "AlbumsByAlbumTitle";
  auto rows = client.Read("Albums", google::cloud::spanner::KeySet::All(),
                          {"AlbumId", "AlbumTitle"}, read_options);
  using RowType = std::tuple<std::int64_t, std::string>;
  for (auto const& row : spanner::StreamOf<RowType>(rows)) {
    if (!row) throw std::runtime_error(row.status().message());
    std::cout << "AlbumId: " << std::get<0>(*row) << "\t";
    std::cout << "AlbumTitle: " << std::get<1>(*row) << "\n";
  }
  std::cout << "Read completed for [spanner_read_data_with_index]\n";
}

Go

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.


func readUsingIndex(ctx context.Context, w io.Writer, client *spanner.Client) error {
	iter := client.Single().ReadUsingIndex(ctx, "Albums", "AlbumsByAlbumTitle", spanner.AllKeys(),
		[]string{"AlbumId", "AlbumTitle"})
	defer iter.Stop()
	for {
		row, err := iter.Next()
		if err == iterator.Done {
			return nil
		}
		if err != nil {
			return err
		}
		var albumID int64
		var albumTitle string
		if err := row.Columns(&albumID, &albumTitle); err != nil {
			return err
		}
		fmt.Fprintf(w, "%d %s\n", albumID, albumTitle)
	}
}

Java

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.

static void readUsingIndex(DatabaseClient dbClient) {
  try (ResultSet resultSet =
      dbClient
          .singleUse()
          .readUsingIndex(
              "Albums",
              "AlbumsByAlbumTitle",
              KeySet.all(),
              Arrays.asList("AlbumId", "AlbumTitle"))) {
    while (resultSet.next()) {
      System.out.printf("%d %s\n", resultSet.getLong(0), resultSet.getString(1));
    }
  }
}

Node.js

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.

// Imports the Google Cloud client library
const {Spanner} = require('@google-cloud/spanner');

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// const projectId = 'my-project-id';
// const instanceId = 'my-instance';
// const databaseId = 'my-database';

// Creates a client
const spanner = new Spanner({
  projectId: projectId,
});

// Gets a reference to a Cloud Spanner instance and database
const instance = spanner.instance(instanceId);
const database = instance.database(databaseId);

const albumsTable = database.table('Albums');

const query = {
  columns: ['AlbumId', 'AlbumTitle'],
  keySet: {
    all: true,
  },
  index: 'AlbumsByAlbumTitle',
};

// Reads the Albums table using an index
try {
  const [rows] = await albumsTable.read(query);

  rows.forEach(row => {
    const json = row.toJSON();
    console.log(`AlbumId: ${json.AlbumId}, AlbumTitle: ${json.AlbumTitle}`);
  });
} catch (err) {
  console.error('ERROR:', err);
} finally {
  // Close the database when finished.
  database.close();
}

PHP

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.

use Google\Cloud\Spanner\SpannerClient;

/**
 * Reads sample data from the database using an index.
 *
 * The index must exist before running this sample. You can add the index
 * by running the `add_index` sample or by running this DDL statement against
 * your database:
 *
 *     CREATE INDEX AlbumsByAlbumTitle ON Albums(AlbumTitle)
 *
 * Example:
 * ```
 * read_data_with_index($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function read_data_with_index($instanceId, $databaseId)
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);

    $keySet = $spanner->keySet(['all' => true]);
    $results = $database->read(
        'Albums',
        $keySet,
        ['AlbumId', 'AlbumTitle'],
        ['index' => 'AlbumsByAlbumTitle']
    );

    foreach ($results->rows() as $row) {
        printf('AlbumId: %s, AlbumTitle: %s' . PHP_EOL,
            $row['AlbumId'], $row['AlbumTitle']);
    }
}

Python

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.

def read_data_with_index(instance_id, database_id):
    """Reads sample data from the database using an index.

    The index must exist before running this sample. You can add the index
    by running the `add_index` sample or by running this DDL statement against
    your database:

        CREATE INDEX AlbumsByAlbumTitle ON Albums(AlbumTitle)

    """
    spanner_client = spanner.Client()
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)

    with database.snapshot() as snapshot:
        keyset = spanner.KeySet(all_=True)
        results = snapshot.read(
            table="Albums",
            columns=("AlbumId", "AlbumTitle"),
            keyset=keyset,
            index="AlbumsByAlbumTitle",
        )

        for row in results:
            print("AlbumId: {}, AlbumTitle: {}".format(*row))

Ruby

To learn how to install and use the client library for Cloud Spanner, see the Cloud Spanner Client Libraries.

# project_id  = "Your Google Cloud project ID"
# instance_id = "Your Spanner instance ID"
# database_id = "Your Spanner database ID"

require "google/cloud/spanner"

spanner = Google::Cloud::Spanner.new project: project_id
client  = spanner.client instance_id, database_id

result = client.read "Albums", [:AlbumId, :AlbumTitle],
                     index: "AlbumsByAlbumTitle"

result.rows.each do |row|
  puts "#{row[:AlbumId]} #{row[:AlbumTitle]}"
end

What's next

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