Esegui query sui dati mediante l'accesso ai campi su uno STRUCT nidificato.
Per saperne di più
Per la documentazione dettagliata che include questo esempio di codice, vedi quanto segue:
Esempio di codice
C++
Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.
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 la pagina relativa alle librerie client di Spanner.
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 la pagina relativa alle librerie client di Spanner.
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 la pagina relativa alle librerie client di Spanner.
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 la pagina relativa alle librerie client di 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);
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: ${json.SongName}`);
});
} catch (err) {
console.error('ERROR:', err);
} finally {
// Close the database when finished.
database.close();
}PHP
Per scoprire come installare e utilizzare la libreria client per Spanner, consulta la pagina relativa alle librerie client di Spanner.
use Google\Cloud\Spanner\SpannerClient;
use Google\Cloud\Spanner\Database;
use Google\Cloud\Spanner\StructType;
use Google\Cloud\Spanner\StructValue;
use Google\Cloud\Spanner\ArrayType;
/**
* Queries sample data from the database using a nested struct field value.
* Example:
* ```
* query_data_with_nested_struct_field($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 la pagina relativa alle librerie client di Spanner.
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 la pagina relativa alle librerie client di 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
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]).to_s, (row[:SongName]).to_s
endPassaggi successivi
Per cercare e filtrare esempi di codice per altri prodotti Google Cloud, consulta il browser di esempio Google Cloud.