Step 6: View the revision history for a document

PDFRSS

Important

End of support notice: Existing customers will be able to use Amazon QLDB until end of support on 07/31/2025. For more details, see Migrate an Amazon QLDB Ledger to Amazon Aurora PostgreSQL.

After modifying registration data for a vehicle in the previous step, you can query the history of all its registered owners and any other updated fields. In this step, you query the revision history of a document in the VehicleRegistration table in your vehicle-registration ledger.

To view the revision history

1. Use the following program (query_history.py) to query the revision history of the VehicleRegistration document with VIN 1N4AL11D75C109151.

   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 datetime import datetime, timedelta
   from logging import basicConfig, getLogger, INFO
   
   from pyqldbsamples.model.sample_data import print_result, get_document_ids, SampleData
   from pyqldbsamples.constants import Constants
   from pyqldbsamples.connect_to_ledger import create_qldb_driver
   
   logger = getLogger(__name__)
   basicConfig(level=INFO)
   
   
   def format_date_time(date_time):
       """
       Format the given date time to a string.
   
       :type date_time: :py:class:`datetime.datetime`
       :param date_time: The date time to format.
   
       :rtype: str
       :return: The formatted date time.
       """
       return date_time.strftime('`%Y-%m-%dT%H:%M:%S.%fZ`')
   
   
   def previous_primary_owners(driver, vin):
       """
       Find previous primary owners for the given VIN in a single transaction.
       In this example, query the `VehicleRegistration` history table to find all previous primary owners for a VIN.
   
       :type driver: :py:class:`pyqldb.driver.qldb_driver.QldbDriver`
       :param driver: An instance of the QldbDriver class.
   
       :type vin: str
       :param vin: VIN to find previous primary owners for.
       """
       person_ids = driver.execute_lambda(lambda executor: get_document_ids(executor,
                                                                            Constants.VEHICLE_REGISTRATION_TABLE_NAME,
                                                                            'VIN', vin))
   
       todays_date = datetime.utcnow() - timedelta(seconds=1)
       three_months_ago = todays_date - timedelta(days=90)
       query = 'SELECT data.Owners.PrimaryOwner, metadata.version FROM history({}, {}, {}) AS h WHERE h.metadata.id = ?'.\
           format(Constants.VEHICLE_REGISTRATION_TABLE_NAME, format_date_time(three_months_ago),
                  format_date_time(todays_date))
   
       for ids in person_ids:
           logger.info("Querying the 'VehicleRegistration' table's history using VIN: {}.".format(vin))
           cursor = driver.execute_lambda(lambda executor: executor.execute_statement(query, ids))
           if not (print_result(cursor)) > 0:
               logger.info('No modification history found within the given time frame for document ID: {}'.format(ids))
   
   
   def main(ledger_name=Constants.LEDGER_NAME):
       """
       Query a table's history for a particular set of documents.
       """
       try:
           with create_qldb_driver(ledger_name) as driver:
               vin = SampleData.VEHICLE_REGISTRATION[0]['VIN']
               previous_primary_owners(driver, vin)
               logger.info('Successfully queried history.')
       except Exception as e:
           logger.exception('Unable to query history to find previous owners.')
           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 datetime import datetime, timedelta
   from logging import basicConfig, getLogger, INFO
   
   from pyqldbsamples.model.sample_data import print_result, get_document_ids, SampleData
   from pyqldbsamples.constants import Constants
   from pyqldbsamples.connect_to_ledger import create_qldb_session
   
   logger = getLogger(__name__)
   basicConfig(level=INFO)
   
   
   def format_date_time(date_time):
       """
       Format the given date time to a string.
   
       :type date_time: :py:class:`datetime.datetime`
       :param date_time: The date time to format.
   
       :rtype: str
       :return: The formatted date time.
       """
       return date_time.strftime('`%Y-%m-%dT%H:%M:%S.%fZ`')
   
   
   def previous_primary_owners(transaction_executor, vin):
       """
       Find previous primary owners for the given VIN in a single transaction.
       In this example, query the `VehicleRegistration` history table to find all previous primary owners for a VIN.
   
       :type transaction_executor: :py:class:`pyqldb.execution.executor.Executor`
       :param transaction_executor: An Executor object allowing for execution of statements within a transaction.
   
       :type vin: str
       :param vin: VIN to find previous primary owners for.
       """
       person_ids = get_document_ids(transaction_executor, Constants.VEHICLE_REGISTRATION_TABLE_NAME, 'VIN', vin)
   
       todays_date = datetime.utcnow() - timedelta(seconds=1)
       three_months_ago = todays_date - timedelta(days=90)
       query = 'SELECT data.Owners.PrimaryOwner, metadata.version FROM history({}, {}, {}) AS h WHERE h.metadata.id = ?'.\
           format(Constants.VEHICLE_REGISTRATION_TABLE_NAME, format_date_time(three_months_ago),
                  format_date_time(todays_date))
   
       for ids in person_ids:
           logger.info("Querying the 'VehicleRegistration' table's history using VIN: {}.".format(vin))
           cursor = transaction_executor.execute_statement(query, ids)
           if not (print_result(cursor)) > 0:
               logger.info('No modification history found within the given time frame for document ID: {}'.format(ids))
   
   
   if __name__ == '__main__':
       """
       Query a table's history for a particular set of documents.
       """
       try:
           with create_qldb_session() as session:
               vin = SampleData.VEHICLE_REGISTRATION[0]['VIN']
               session.execute_lambda(lambda lambda_executor: previous_primary_owners(lambda_executor, vin),
                                      lambda retry_attempt: logger.info('Retrying due to OCC conflict...'))
               logger.info('Successfully queried history.')
       except Exception:
           logger.exception('Unable to query history to find previous owners.')

   Note

   • You can view the revision history of a document by querying the built-in History function in the following syntax.

     SELECT * FROM history( table_name [, `start-time` [, `end-time` ] ] ) AS h
     [ WHERE h.metadata.id = 'id' ]

   • The start-time and end-time are both optional. They're Amazon Ion literal values that can be denoted with backticks (`...`). To learn more, see Querying Ion with PartiQL in Amazon QLDB.

   • As a best practice, qualify a history query with both a date range (start-time and end-time) and a document ID (metadata.id). QLDB processes SELECT queries in transactions, which are subject to a transaction timeout limit.

     QLDB history is indexed by document ID, and you can't create additional history indexes at this time. History queries that include a start time and end time gain the benefit of date range qualification.

2. To run the program, enter the following command.

   python query_history.py

To cryptographically verify a document revision in the vehicle-registration ledger, proceed to Step 7: Verify a document in a ledger.