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# Etapa 6: Visualizar o histórico de revisão de um documento
**Importante**
Aviso de fim do suporte: os clientes existentes poderão usar o Amazon QLDB até o final do suporte em 31/07/2025. Para obter mais detalhes, consulte [Migrar um Amazon QLDB Ledger para o Amazon](https://aws.amazon.com/blogs/database/migrate-an-amazon-qldb-ledger-to-amazon-aurora-postgresql/) Aurora PostgreSQL.
Depois de modificar os dados de registro para um veículo na etapa anterior, você pode consultar o histórico de todos os proprietários registrados e quaisquer outros campos atualizados. Nesta etapa, você consulta o histórico de revisão de um documento na tabela `VehicleRegistration` do ledger `vehicle-registration`.
**Visualizar o histórico de revisão**
1. Analise o programa a seguir (`QueryHistory.java`).
------
#### [ 2.x ]
```
/*
* Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: MIT-0
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of this
* software and associated documentation files (the "Software"), to deal in the Software
* without restriction, including without limitation the rights to use, copy, modify,
* merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package software.amazon.qldb.tutorial;
import java.io.IOException;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.amazon.ion.IonValue;
import software.amazon.qldb.Result;
import software.amazon.qldb.TransactionExecutor;
import software.amazon.qldb.tutorial.model.SampleData;
import software.amazon.qldb.tutorial.model.VehicleRegistration;
/**
* Query a table's history for a particular set of documents.
*
* This code expects that you have AWS credentials setup per:
* http://docs.aws.amazon.com/java-sdk/latest/developer-guide/setup-credentials.html
*/
public final class QueryHistory {
public static final Logger log = LoggerFactory.getLogger(QueryHistory.class);
private static final int THREE_MONTHS = 90;
private QueryHistory() { }
/**
* In this example, query the 'VehicleRegistration' history table to find all previous primary owners for a VIN.
*
* @param txn
* The {@link TransactionExecutor} for lambda execute.
* @param vin
* VIN to find previous primary owners for.
* @param query
* The query to find previous primary owners.
* @throws IllegalStateException if failed to convert document ID to an {@link IonValue}.
*/
public static void previousPrimaryOwners(final TransactionExecutor txn, final String vin, final String query) {
try {
final String docId = VehicleRegistration.getDocumentIdByVin(txn, vin);
log.info("Querying the 'VehicleRegistration' table's history using VIN: {}...", vin);
final Result result = txn.execute(query, Constants.MAPPER.writeValueAsIonValue(docId));
ScanTable.printDocuments(result);
} catch (IOException ioe) {
throw new IllegalStateException(ioe);
}
}
public static void main(final String... args) {
final String threeMonthsAgo = Instant.now().minus(THREE_MONTHS, ChronoUnit.DAYS).toString();
final String query = String.format("SELECT data.Owners.PrimaryOwner, metadata.version "
+ "FROM history(VehicleRegistration, `%s`) "
+ "AS h WHERE h.metadata.id = ?", threeMonthsAgo);
ConnectToLedger.getDriver().execute(txn -> {
final String vin = SampleData.VEHICLES.get(0).getVin();
previousPrimaryOwners(txn, vin, query);
});
log.info("Successfully queried history.");
}
}
```
------
#### [ 1.x ]
```
/*
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: MIT-0
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of this
* software and associated documentation files (the "Software"), to deal in the Software
* without restriction, including without limitation the rights to use, copy, modify,
* merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package software.amazon.qldb.tutorial;
import com.amazon.ion.IonValue;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import software.amazon.qldb.QldbSession;
import software.amazon.qldb.Result;
import software.amazon.qldb.TransactionExecutor;
import software.amazon.qldb.tutorial.model.SampleData;
import software.amazon.qldb.tutorial.model.VehicleRegistration;
import java.io.IOException;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.Collections;
import java.util.List;
/**
* Query a table's history for a particular set of documents.
*
* This code expects that you have AWS credentials setup per:
* http://docs.aws.amazon.com/java-sdk/latest/developer-guide/setup-credentials.html
*/
public final class QueryHistory {
public static final Logger log = LoggerFactory.getLogger(QueryHistory.class);
private static final int THREE_MONTHS = 90;
private QueryHistory() { }
/**
* In this example, query the 'VehicleRegistration' history table to find all previous primary owners for a VIN.
*
* @param txn
* The {@link TransactionExecutor} for lambda execute.
* @param vin
* VIN to find previous primary owners for.
* @param query
* The query to find previous primary owners.
* @throws IllegalStateException if failed to convert document ID to an {@link IonValue}.
*/
public static void previousPrimaryOwners(final TransactionExecutor txn, final String vin, final String query) {
try {
final String docId = VehicleRegistration.getDocumentIdByVin(txn, vin);
final List parameters = Collections.singletonList(Constants.MAPPER.writeValueAsIonValue(docId));
log.info("Querying the 'VehicleRegistration' table's history using VIN: {}...", vin);
final Result result = txn.execute(query, parameters);
ScanTable.printDocuments(result);
} catch (IOException ioe) {
throw new IllegalStateException(ioe);
}
}
public static void main(final String... args) {
final String threeMonthsAgo = Instant.now().minus(THREE_MONTHS, ChronoUnit.DAYS).toString();
final String query = String.format("SELECT data.Owners.PrimaryOwner, metadata.version "
+ "FROM history(VehicleRegistration, `%s`) "
+ "AS h WHERE h.metadata.id = ?", threeMonthsAgo);
ConnectToLedger.getDriver().execute(txn -> {
final String vin = SampleData.VEHICLES.get(0).getVin();
previousPrimaryOwners(txn, vin, query);
}, (retryAttempt) -> log.info("Retrying due to OCC conflict..."));
log.info("Successfully queried history.");
}
}
```
------
**nota**
Você pode visualizar o histórico de revisões de um documento consultando a sintaxe [Função de histórico](working.history.md#working.history.function) incorporada a seguir.
```
SELECT * FROM history( table_name [, `start-time` [, `end-time` ] ] ) AS h
[ WHERE h.metadata.id = 'id' ]
```
A *hora de início* e a *hora de término* são opcionais. São valores literais do Amazon Ion que podem ser indicados com acentos graves (``...``). Para saber mais, consulte [Consultar o Ion com o PartiQL no Amazon QLDB](ql-reference.query.md).
Como prática recomendada, qualifique uma consulta de histórico com um intervalo de datas (*hora de início* e *hora de término*) e um ID de documentos (`metadata.id`). O QLDB processa consultas `SELECT` em transações, que estão sujeitas a um [limite de tempo de transação](limits.md#limits.fixed).
O histórico do QLDB é indexado por ID do documento, e você não pode criar índices de histórico adicionais no momento. As consultas de histórico que incluem uma hora de início e uma hora de término ganham o benefício da qualificação por intervalo de datas.
1. Compile e execute o programa a seguir (`QueryHistory.java`) para consultar o histórico de revisão do `VehicleRegistration` documento com o VIN `1N4AL11D75C109151`.
Para verificar uma revisão de documento criptograficamente no ledger `vehicle-registration`, vá para [Etapa 7: verificar um documento em um ledger](getting-started.java.step-7.md).