Etapa 4: consultar as tabelas em um ledger

Depois de criar tabelas em um ledger do Amazon QLDB e carregá-las com dados, você pode executar consultas para revisar os dados de registro do veículo que você acabou de inserir. O QLDB usa o PartiQL como sua linguagem de consulta e o Amazon Ion como seu modelo de dados orientado a documentos.

O partiQL é uma linguagem de consulta de código aberto compatível com SQL que foi estendida para funcionar com o Ion. Com o partiQL, você pode inserir, consultar e gerenciar seus dados com operadores SQL conhecidos. O Amazon Ion é um superconjunto do JSON. O Ion é um formato de dados de código aberto baseado em documentos que oferece a flexibilidade de armazenar e processar dados estruturados, semiestruturados e aninhados.

Em seguida, você pode usar instruções SELECT para ler os dados das tabelas no vehicle-registration ledger.

Atenção

Quando você executa uma consulta no QLDB sem uma pesquisa indexada, ela invoca uma verificação completa da tabela. O partiQL suporta essas consultas porque é compatível com SQL. No entanto, não execute varreduras de tabela para casos de uso de produção no QLDB. Verificações de tabela podem causar problemas de performance em tabelas grandes, incluindo conflitos de simultaneidade e tempos limite de transação.

Para evitar verificações de tabelas, você deve executar instruções com uma cláusula de predicado WHERE usando um operador de igualdade em um campo indexado ou em uma ID de documento, por exemplo, WHERE indexedField = 123 ou WHERE indexedField IN (456, 789). Para obter mais informações, consulte Otimizar a performance da consulta.

Para consultar as tabelas

1. Use o seguinte programa (find_vehicles.py) para consultar todos os veículos registrados sob uma pessoa em seu ledger.

   3.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.
   #
   # This code expects that you have AWS credentials setup per:
   # https://boto3.amazonaws.com/v1/documentation/api/latest/guide/quickstart.html
   from logging import basicConfig, getLogger, INFO
   
   from pyqldbsamples.model.sample_data import get_document_ids, print_result, SampleData
   from pyqldbsamples.constants import Constants
   from pyqldbsamples.connect_to_ledger import create_qldb_driver
   
   logger = getLogger(__name__)
   basicConfig(level=INFO)
   
   
   def find_vehicles_for_owner(driver, gov_id):
       """
       Find vehicles registered under a driver using their government ID.
   
       :type driver: :py:class:`pyqldb.driver.qldb_driver.QldbDriver`
       :param driver: An instance of the QldbDriver class.
   
       :type gov_id: str
       :param gov_id: The owner's government ID.
       """
       document_ids = driver.execute_lambda(lambda executor: get_document_ids(executor, Constants.PERSON_TABLE_NAME,
                                                                              'GovId', gov_id))
   
       query = "SELECT Vehicle FROM Vehicle INNER JOIN VehicleRegistration AS r " \
               "ON Vehicle.VIN = r.VIN WHERE r.Owners.PrimaryOwner.PersonId = ?"
   
       for ids in document_ids:
           cursor = driver.execute_lambda(lambda executor: executor.execute_statement(query, ids))
           logger.info('List of Vehicles for owner with GovId: {}...'.format(gov_id))
           print_result(cursor)
   
   
   def main(ledger_name=Constants.LEDGER_NAME):
       """
       Find all vehicles registered under a person.
       """
       try:
           with create_qldb_driver(ledger_name) as driver:
               # Find all vehicles registered under a person.
               gov_id = SampleData.PERSON[0]['GovId']
               find_vehicles_for_owner(driver, gov_id)
       except Exception as e:
           logger.exception('Error getting vehicles for owner.')
           raise e
   
   
   if __name__ == '__main__':
       main()

   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.
   #
   # This code expects that you have AWS credentials setup per:
   # https://boto3.amazonaws.com/v1/documentation/api/latest/guide/quickstart.html
   from logging import basicConfig, getLogger, INFO
   
   from pyqldbsamples.model.sample_data import get_document_ids, print_result, SampleData
   from pyqldbsamples.constants import Constants
   from pyqldbsamples.connect_to_ledger import create_qldb_session
   
   logger = getLogger(__name__)
   basicConfig(level=INFO)
   
   
   def find_vehicles_for_owner(transaction_executor, gov_id):
       """
       Find vehicles registered under a driver using their government ID.
   
       :type transaction_executor: :py:class:`pyqldb.execution.executor.Executor`
       :param transaction_executor: An Executor object allowing for execution of statements within a transaction.
   
       :type gov_id: str
       :param gov_id: The owner's government ID.
       """
       document_ids = get_document_ids(transaction_executor, Constants.PERSON_TABLE_NAME, 'GovId', gov_id)
   
       query = "SELECT Vehicle FROM Vehicle INNER JOIN VehicleRegistration AS r " \
               "ON Vehicle.VIN = r.VIN WHERE r.Owners.PrimaryOwner.PersonId = ?"
   
       for ids in document_ids:
           cursor = transaction_executor.execute_statement(query, ids)
           logger.info('List of Vehicles for owner with GovId: {}...'.format(gov_id))
           print_result(cursor)
   
   
   if __name__ == '__main__':
       """
       Find all vehicles registered under a person.
       """
       try:
           with create_qldb_session() as session:
               # Find all vehicles registered under a person.
               gov_id = SampleData.PERSON[0]['GovId']
               session.execute_lambda(lambda executor: find_vehicles_for_owner(executor, gov_id),
                                      lambda retry_attempt: logger.info('Retrying due to OCC conflict...'))
       except Exception:
           logger.exception('Error getting vehicles for owner.')

   nota

   Primeiro, esse programa consulta a tabela Person para o documento GovId LEWISR261LL para obter seu campo de metadados id.

   Em seguida, usa esse documento id como uma chave externa para consultar a tabela VehicleRegistration, PrimaryOwner.PersonId. Ele também junta VehicleRegistration à tabela Vehicle no campo VIN.

2. Para executar o programa, digite o comando a seguir.

   python find_vehicles.py

Para saber mais sobre a modificação de documentos nas tabelas do vehicle-registration ledger, consulte Etapa 5: Modificar documentos em um ledger.