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Lee datos inactivos

Lee los datos inactivos.

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Para obtener documentación en la que se incluye esta muestra de código, consulta lo siguiente:

Lecturas fuera de las transacciones

Muestra de código

C++

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.

Para autenticarte en Spanner, configura las credenciales predeterminadas de la aplicación. Si deseas obtener más información, consulta Configura la autenticación para un entorno de desarrollo local.

void ReadStaleData(google::cloud::spanner::Client client) {
  namespace spanner = ::google::cloud::spanner;
  // The timestamp chosen using the `exact_staleness` parameter is bounded
  // below by the creation time of the database, so the visible state may only
  // include that generated by the `extra_statements` executed atomically with
  // the creation of the database. Here we at least know `Albums` exists.
  auto opts = spanner::Transaction::ReadOnlyOptions(std::chrono::seconds(15));
  auto read_only = spanner::MakeReadOnlyTransaction(std::move(opts));

  spanner::SqlStatement select(
      "SELECT SingerId, AlbumId, AlbumTitle FROM Albums");
  using RowType = std::tuple<std::int64_t, std::int64_t, std::string>;

  auto rows = client.ExecuteQuery(std::move(read_only), std::move(select));
  for (auto& row : spanner::StreamOf<RowType>(rows)) {
    if (!row) throw std::move(row).status();
    std::cout << "SingerId: " << std::get<0>(*row)
              << " AlbumId: " << std::get<1>(*row)
              << " AlbumTitle: " << std::get<2>(*row) << "\n";
  }
}

C#

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.


using Google.Cloud.Spanner.Data;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

public class ReadStaleDataAsyncSample
{
    public class Album
    {
        public int SingerId { get; set; }
        public int AlbumId { get; set; }
        public long? MarketingBudget { get; set; }
    }

    public async Task<List<Album>> ReadStaleDataAsync(string projectId, string instanceId, string databaseId)
    {
        string connectionString = $"Data Source=projects/{projectId}/instances/{instanceId}/databases/{databaseId}";

        using var connection = new SpannerConnection(connectionString);
        await connection.OpenAsync();

        var staleness = TimestampBound.OfExactStaleness(TimeSpan.FromSeconds(15));
        using var transaction = await connection.BeginTransactionAsync(SpannerTransactionCreationOptions.ForTimestampBoundReadOnly(staleness), cancellationToken: default);
        using var cmd = connection.CreateSelectCommand("SELECT SingerId, AlbumId, MarketingBudget FROM Albums");
        cmd.Transaction = transaction;

        var albums = new List<Album>();
        using var reader = await cmd.ExecuteReaderAsync();
        while (await reader.ReadAsync())
        {
            albums.Add(new Album
            {
                SingerId = reader.GetFieldValue<int>("SingerId"),
                AlbumId = reader.GetFieldValue<int>("AlbumId"),
                MarketingBudget = reader.IsDBNull(reader.GetOrdinal("MarketingBudget")) ? 0 : reader.GetFieldValue<long>("MarketingBudget")
            });
        }
        return albums;
    }
}

Go

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.


import (
	"context"
	"fmt"
	"io"
	"time"

	"cloud.google.com/go/spanner"
	"google.golang.org/api/iterator"
)

func readStaleData(w io.Writer, db string) error {
	ctx := context.Background()
	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	ro := client.ReadOnlyTransaction().WithTimestampBound(spanner.ExactStaleness(15 * time.Second))
	defer ro.Close()

	iter := ro.Read(ctx, "Albums", spanner.AllKeys(), []string{"SingerId", "AlbumId", "AlbumTitle"})
	defer iter.Stop()
	for {
		row, err := iter.Next()
		if err == iterator.Done {
			return nil
		}
		if err != nil {
			return err
		}
		var singerID int64
		var albumID int64
		var albumTitle string
		if err := row.Columns(&singerID, &albumID, &albumTitle); err != nil {
			return err
		}
		fmt.Fprintf(w, "%d %d %s\n", singerID, albumID, albumTitle)
	}
}

Java

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.

static void readStaleData(DatabaseClient dbClient) {
  try (ResultSet resultSet =
      dbClient
          .singleUse(TimestampBound.ofExactStaleness(15, TimeUnit.SECONDS))
          .read(
              "Albums", KeySet.all(), Arrays.asList("SingerId", "AlbumId", "MarketingBudget"))) {
    while (resultSet.next()) {
      System.out.printf(
          "%d %d %s\n",
          resultSet.getLong(0),
          resultSet.getLong(1),
          resultSet.isNull(2) ? "NULL" : resultSet.getLong("MarketingBudget"));
    }
  }
}

Node.js

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.

// 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);

// Reads rows from the Albums table
const albumsTable = database.table('Albums');

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

const options = {
  // Guarantees that all writes committed more than 15 seconds ago are visible
  exactStaleness: 15,
};

try {
  const [rows] = await albumsTable.read(query, options);

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

PHP

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.

use Google\Cloud\Spanner\Duration;
use Google\Cloud\Spanner\SpannerClient;

/**
 * Reads sample data from the database.  The data is exactly 15 seconds stale.
 * Guarantees that all writes committed more than 15 seconds ago are visible.
 * Example:
 * ```
 * read_stale_data
 *($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function read_stale_data(string $instanceId, string $databaseId): void
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);
    $keySet = $spanner->keySet(['all' => true]);
    $results = $database->read(
        'Albums',
        $keySet,
        ['SingerId', 'AlbumId', 'AlbumTitle'],
        ['exactStaleness' => new Duration(15)]
    );

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

Python

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.

def read_stale_data(instance_id, database_id):
    """Reads sample data from the database. The data is exactly 15 seconds
    stale."""
    import datetime

    spanner_client = spanner.Client()
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)
    staleness = datetime.timedelta(seconds=15)

    with database.snapshot(exact_staleness=staleness) as snapshot:
        keyset = spanner.KeySet(all_=True)
        results = snapshot.read(
            table="Albums",
            columns=("SingerId", "AlbumId", "MarketingBudget"),
            keyset=keyset,
        )

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

Ruby

Para obtener información sobre cómo instalar y usar la biblioteca cliente de Spanner, consulta Bibliotecas cliente de Spanner.

# 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

# Perform a read with a data staleness of 15 seconds
client.snapshot staleness: 15 do |snapshot|
  snapshot.read("Albums", [:SingerId, :AlbumId, :AlbumTitle]).rows.each do |row|
    puts "#{row[:SingerId]} #{row[:AlbumId]} #{row[:AlbumTitle]}"
  end
end

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