Accesso ai campi su uno STRUCT

Esegui una query sui dati utilizzando l'accesso al campo su uno STRUCT.

Per saperne di più

Per la documentazione dettagliata che include questo esempio di codice, vedi quanto segue:

• Lavorare con gli oggetti STRUCT

Esempio di codice

C++

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

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

  // Cloud Spanner STRUCT<> with named fields is represented as
  // tuple<pair<string, T>...>. Create a type alias for this example:
  using SingerName = std::tuple<std::pair<std::string, std::string>,
                                std::pair<std::string, std::string>>;
  SingerName name({"FirstName", "Elena"}, {"LastName", "Campbell"});

  auto rows = client.ExecuteQuery(spanner::SqlStatement(
      "SELECT SingerId FROM Singers WHERE FirstName = @name.FirstName",
      {{"name", spanner::Value(name)}}));

  for (auto& row : spanner::StreamOf<std::tuple<std::int64_t>>(rows)) {
    if (!row) throw std::move(row).status();
    std::cout << "SingerId: " << std::get<0>(*row) << "\n";
  }
  std::cout << "Query completed for"
            << " [spanner_field_access_on_struct_parameters]\n";
}

C#

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

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

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

        var structParam = new SpannerStruct
        {
            { "FirstName", SpannerDbType.String, "Elena" },
            { "LastName", SpannerDbType.String, "Campbell" },
        };

        var singerIds = new List<int>();
        using var connection = new SpannerConnection(connectionString);
        using var cmd = connection.CreateSelectCommand("SELECT SingerId FROM Singers WHERE FirstName = @name.FirstName");

        cmd.Parameters.Add("name", structParam.GetSpannerDbType(), structParam);
        using var reader = await cmd.ExecuteReaderAsync();
        while (await reader.ReadAsync())
        {
            singerIds.Add(reader.GetFieldValue<int>("SingerId"));
        }
        return singerIds;
    }
}

Go

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

import (
	"context"
	"fmt"
	"io"

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

func queryWithStructField(w io.Writer, db string) error {
	ctx := context.Background()

	client, err := spanner.NewClient(ctx, db)
	if err != nil {
		return err
	}
	defer client.Close()

	type structParam struct {
		FirstName string
		LastName  string
	}
	var singerInfo = structParam{"Elena", "Campbell"}
	stmt := spanner.Statement{
		SQL: `SELECT SingerId FROM SINGERS
			WHERE FirstName = @name.FirstName`,
		Params: map[string]interface{}{"name": singerInfo},
	}
	iter := client.Single().Query(ctx, stmt)
	defer iter.Stop()
	for {
		row, err := iter.Next()
		if err == iterator.Done {
			return nil
		}
		if err != nil {
			return err
		}
		var singerID int64
		if err := row.Columns(&singerID); err != nil {
			return err
		}
		fmt.Fprintf(w, "%d\n", singerID)
	}
}

Java

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

static void queryStructField(DatabaseClient dbClient) {
  Statement s =
      Statement.newBuilder("SELECT SingerId FROM Singers WHERE FirstName = @name.FirstName")
          .bind("name")
          .to(
              Struct.newBuilder()
                  .set("FirstName")
                  .to("Elena")
                  .set("LastName")
                  .to("Campbell")
                  .build())
          .build();
  try (ResultSet resultSet = dbClient.singleUse().executeQuery(s)) {
    while (resultSet.next()) {
      System.out.printf("%d\n", resultSet.getLong("SingerId"));
    }
  }
}

Node.js

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

// 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 nameStruct = Spanner.struct({
  FirstName: 'Elena',
  LastName: 'Campbell',
});
const query = {
  sql: 'SELECT SingerId FROM Singers WHERE FirstName = @name.FirstName',
  params: {
    name: nameStruct,
  },
};

// Queries rows from the Singers table
try {
  const [rows] = await database.run(query);

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

PHP

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

use Google\Cloud\Spanner\SpannerClient;
use Google\Cloud\Spanner\Database;
use Google\Cloud\Spanner\StructType;

/**
 * Queries sample data from the database using a struct field value.
 * Example:
 * ```
 * query_data_with_struct_field($instanceId, $databaseId);
 * ```
 *
 * @param string $instanceId The Spanner instance ID.
 * @param string $databaseId The Spanner database ID.
 */
function query_data_with_struct_field(string $instanceId, string $databaseId): void
{
    $spanner = new SpannerClient();
    $instance = $spanner->instance($instanceId);
    $database = $instance->database($databaseId);

    $nameType = (new StructType)
        ->add('FirstName', Database::TYPE_STRING)
        ->add('LastName', Database::TYPE_STRING);
    $results = $database->execute(
        'SELECT SingerId FROM Singers WHERE FirstName = @name.FirstName',
        [
            'parameters' => [
                'name' => [
                    'FirstName' => 'Elena',
                    'LastName' => 'Campbell'
                ]
            ],
            'types' => [
                'name' => $nameType
            ]
        ]
    );
    foreach ($results as $row) {
        printf('SingerId: %s' . PHP_EOL,
            $row['SingerId']);
    }
}

Python

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

def query_struct_field(instance_id, database_id):
    """Query a table using field access on a STRUCT parameter."""
    spanner_client = spanner.Client()
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)

    name_type = param_types.Struct(
        [
            param_types.StructField("FirstName", param_types.STRING),
            param_types.StructField("LastName", param_types.STRING),
        ]
    )

    with database.snapshot() as snapshot:
        results = snapshot.execute_sql(
            "SELECT SingerId FROM Singers " "WHERE FirstName = @name.FirstName",
            params={"name": ("Elena", "Campbell")},
            param_types={"name": name_type},
        )

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

Ruby

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.

Visualizza su GitHub Feedback

# 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

name_struct = { FirstName: "Elena", LastName: "Campbell" }
client.execute(
  "SELECT SingerId FROM Singers WHERE FirstName = @name.FirstName",
  params: { name: name_struct }
).rows.each do |row|
  puts row[:SingerId].to_s
end

Passaggi successivi

Per cercare e filtrare esempi di codice per altri prodotti Google Cloud, consulta il browser di esempio Google Cloud.