Accesso ai campi su STRUCT nidificato

Esegui query sui dati utilizzando l'accesso ai campi su uno STRUCT nidificato.

Per saperne di più

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

Esempio di codice

C++

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta Librerie client di Spanner.

Per eseguire l'autenticazione su Spanner, configura Credenziali predefinite dell'applicazione. Per ulteriori informazioni, consulta Configurare l'autenticazione per un ambiente di sviluppo locale. 

void FieldAccessOnNestedStruct(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 SingerFullName = std::tuple<std::pair<std::string, std::string>,
                                    std::pair<std::string, std::string>>;
  auto make_name = [](std::string fname, std::string lname) {
    return SingerFullName({"FirstName", std::move(fname)},
                          {"LastName", std::move(lname)});
  };
  using SongInfo =
      std::tuple<std::pair<std::string, std::string>,
                 std::pair<std::string, std::vector<SingerFullName>>>;
  auto songinfo = SongInfo(
      {"SongName", "Imagination"},
      {"ArtistNames",
       {make_name("Elena", "Campbell"), make_name("Hannah", "Harris")}});

  auto rows = client.ExecuteQuery(spanner::SqlStatement(
      "SELECT SingerId, @songinfo.SongName FROM Singers"
      " WHERE STRUCT<FirstName STRING, LastName STRING>(FirstName, LastName)"
      "    IN UNNEST(@songinfo.ArtistNames)",
      {{"songinfo", spanner::Value(songinfo)}}));

  using RowType = std::tuple<std::int64_t, std::string>;
  for (auto& row : spanner::StreamOf<RowType>(rows)) {
    if (!row) throw std::move(row).status();
    std::cout << "SingerId: " << std::get<0>(*row)
              << " SongName: " << std::get<1>(*row) << "\n";
  }
  std::cout << "Query completed for [spanner_field_access_on_nested_struct]\n";
}

C#

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta Librerie client Spanner.

Per autenticarti a Spanner, configura le credenziali predefinite dell'applicazione. Per ulteriori informazioni, vedi Configura l'autenticazione per un ambiente di sviluppo locale. 


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

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

        SpannerStruct name1 = new SpannerStruct
        {
            { "FirstName", SpannerDbType.String, "Elena" },
            { "LastName", SpannerDbType.String, "Campbell" }
        };
        SpannerStruct name2 = new SpannerStruct
        {
            { "FirstName", SpannerDbType.String, "Hannah" },
            { "LastName", SpannerDbType.String, "Harris" }
        };
        SpannerStruct songInfo = new SpannerStruct
        {
            { "song_name", SpannerDbType.String, "Imagination" },
            { "artistNames", SpannerDbType.ArrayOf(name1.GetSpannerDbType()), new[] { name1, name2 } }
        };

        var singerIds = new List<int>();
        using var connection = new SpannerConnection(connectionString);
        using var cmd = connection.CreateSelectCommand(
            "SELECT SingerId, @song_info.song_name "
            + "FROM Singers WHERE STRUCT<FirstName STRING, LastName STRING>(FirstName, LastName) "
            + "IN UNNEST(@song_info.artistNames)");

        cmd.Parameters.Add("song_info", songInfo.GetSpannerDbType(), songInfo);

        using var reader = await cmd.ExecuteReaderAsync();
        while (await reader.ReadAsync())
        {
            var singerId = reader.GetFieldValue<int>("SingerId");
            singerIds.Add(singerId);
            Console.WriteLine($"SingerId: {singerId}");
            Console.WriteLine($"Song Name: {reader.GetFieldValue<string>(1)}");
        }
        return singerIds;
    }
}

Go

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta Librerie client Spanner.

Per autenticarti a Spanner, configura le credenziali predefinite dell'applicazione. Per ulteriori informazioni, vedi Configura l'autenticazione per un ambiente di sviluppo locale. 


import (
	"context"
	"fmt"
	"io"

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

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

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

	type nameType struct {
		FirstName string
		LastName  string
	}
	type songInfoStruct struct {
		SongName    string
		ArtistNames []nameType
	}
	var songInfo = songInfoStruct{
		SongName: "Imagination",
		ArtistNames: []nameType{
			{FirstName: "Elena", LastName: "Campbell"},
			{FirstName: "Hannah", LastName: "Harris"},
		},
	}
	stmt := spanner.Statement{
		SQL: `SELECT SingerId, @songinfo.SongName FROM Singers
			WHERE STRUCT<FirstName STRING, LastName STRING>(FirstName, LastName)
			IN UNNEST(@songinfo.ArtistNames)`,
		Params: map[string]interface{}{"songinfo": songInfo},
	}
	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
		var songName string
		if err := row.Columns(&singerID, &songName); err != nil {
			return err
		}
		fmt.Fprintf(w, "%d %s\n", singerID, songName)
	}
}

Java

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta Librerie client Spanner.

Per autenticarti a Spanner, configura le credenziali predefinite dell'applicazione. Per ulteriori informazioni, consulta Configurare l'autenticazione per un ambiente di sviluppo locale. 

static void queryNestedStructField(DatabaseClient dbClient) {
  Type nameType =
      Type.struct(
          Arrays.asList(
              StructField.of("FirstName", Type.string()),
              StructField.of("LastName", Type.string())));

  Struct songInfo =
      Struct.newBuilder()
          .set("song_name")
          .to("Imagination")
          .set("artistNames")
          .toStructArray(
              nameType,
              Arrays.asList(
                  Struct.newBuilder()
                      .set("FirstName")
                      .to("Elena")
                      .set("LastName")
                      .to("Campbell")
                      .build(),
                  Struct.newBuilder()
                      .set("FirstName")
                      .to("Hannah")
                      .set("LastName")
                      .to("Harris")
                      .build()))
          .build();
  Statement s =
      Statement.newBuilder(
              "SELECT SingerId, @song_info.song_name "
                  + "FROM Singers WHERE "
                  + "STRUCT<FirstName STRING, LastName STRING>(FirstName, LastName) "
                  + "IN UNNEST(@song_info.artistNames)")
          .bind("song_info")
          .to(songInfo)
          .build();
  try (ResultSet resultSet = dbClient.singleUse().executeQuery(s)) {
    while (resultSet.next()) {
      System.out.printf("%d %s\n", resultSet.getLong("SingerId"), resultSet.getString(1));
    }
  }
}

Node.js

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta Librerie client Spanner.

Per eseguire l'autenticazione su Spanner, configura Credenziali predefinite dell'applicazione. Per ulteriori informazioni, consulta Configurare l'autenticazione per un ambiente di sviluppo locale. 

// 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 nameType = {
  type: 'struct',
  fields: [
    {
      name: 'FirstName',
      type: 'string',
    },
    {
      name: 'LastName',
      type: 'string',
    },
  ],
};

// Creates Song info STRUCT with a nested ArtistNames array
const songInfoType = {
  type: 'struct',
  fields: [
    {
      name: 'SongName',
      type: 'string',
    },
    {
      name: 'ArtistNames',
      type: 'array',
      child: nameType,
    },
  ],
};

const songInfoStruct = Spanner.struct({
  SongName: 'Imagination',
  ArtistNames: [
    Spanner.struct({FirstName: 'Elena', LastName: 'Campbell'}),
    Spanner.struct({FirstName: 'Hannah', LastName: 'Harris'}),
  ],
});

const query = {
  sql:
    'SELECT SingerId, @songInfo.SongName FROM Singers ' +
    'WHERE STRUCT<FirstName STRING, LastName STRING>(FirstName, LastName) ' +
    'IN UNNEST(@songInfo.ArtistNames)',
  params: {
    songInfo: songInfoStruct,
  },
  types: {
    songInfo: songInfoType,
  },
};

// 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}, SongName: ${json.SongName}`);
  });
} 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 Librerie client Spanner.

Per autenticarti a Spanner, configura le credenziali predefinite dell'applicazione. Per ulteriori informazioni, consulta Configurare l'autenticazione per un ambiente di sviluppo locale. 

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

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

    $nameType = new ArrayType(
        (new StructType)
            ->add('FirstName', Database::TYPE_STRING)
            ->add('LastName', Database::TYPE_STRING)
    );
    $songInfoType = (new StructType)
        ->add('SongName', Database::TYPE_STRING)
        ->add('ArtistNames', $nameType);
    $nameStructValue1 = (new StructValue)
        ->add('FirstName', 'Elena')
        ->add('LastName', 'Campbell');
    $nameStructValue2 = (new StructValue)
        ->add('FirstName', 'Hannah')
        ->add('LastName', 'Harris');
    $songInfoValues = (new StructValue)
        ->add('SongName', 'Imagination')
        ->add('ArtistNames', [$nameStructValue1, $nameStructValue2]);
    $results = $database->execute(
        'SELECT SingerId, @song_info.SongName FROM Singers ' .
        'WHERE STRUCT<FirstName STRING, LastName STRING>(FirstName, LastName) ' .
        'IN UNNEST(@song_info.ArtistNames)',
        [
            'parameters' => [
                'song_info' => $songInfoValues
            ],
            'types' => [
                'song_info' => $songInfoType
            ]
        ]
    );
    foreach ($results as $row) {
        printf('SingerId: %s SongName: %s' . PHP_EOL,
            $row['SingerId'], $row['SongName']);
    }
}

Python

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta Librerie client Spanner.

Per autenticarti a Spanner, configura le credenziali predefinite dell'applicazione. Per ulteriori informazioni, consulta Configurare l'autenticazione per un ambiente di sviluppo locale. 

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

    song_info_type = param_types.Struct(
        [
            param_types.StructField("SongName", param_types.STRING),
            param_types.StructField(
                "ArtistNames",
                param_types.Array(
                    param_types.Struct(
                        [
                            param_types.StructField("FirstName", param_types.STRING),
                            param_types.StructField("LastName", param_types.STRING),
                        ]
                    )
                ),
            ),
        ]
    )

    song_info = ("Imagination", [("Elena", "Campbell"), ("Hannah", "Harris")])

    with database.snapshot() as snapshot:
        results = snapshot.execute_sql(
            "SELECT SingerId, @song_info.SongName "
            "FROM Singers WHERE "
            "STRUCT<FirstName STRING, LastName STRING>"
            "(FirstName, LastName) "
            "IN UNNEST(@song_info.ArtistNames)",
            params={"song_info": song_info},
            param_types={"song_info": song_info_type},
        )

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

Ruby

Per scoprire come installare e utilizzare la libreria client per Spanner, consulta Librerie client di Spanner.

Per eseguire l'autenticazione su Spanner, configura Credenziali predefinite dell'applicazione. Per ulteriori informazioni, vedi Configura l'autenticazione per un ambiente di sviluppo locale. 

# 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_type = client.fields FirstName: :STRING, LastName: :STRING

song_info_struct = {
  SongName:    "Imagination",
  ArtistNames: [name_type.struct(["Elena", "Campbell"]), name_type.struct(["Hannah", "Harris"])]
}

client.execute(
  "SELECT SingerId, @song_info.SongName " \
  "FROM Singers WHERE STRUCT<FirstName STRING, LastName STRING>(FirstName, LastName) " \
  "IN UNNEST(@song_info.ArtistNames)",
  params: { song_info: song_info_struct }
).rows.each do |row|
  puts (row[:SingerId]), (row[:SongName])
end

Passaggi successivi

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