步骤 6：查看文档修订历史记录

在上一步中修改车辆注册数据后，您可查询其所有注册车主的历史记录以及任何其他更新的字段。在此步骤中，您将在 vehicle-registration 分类账的 VehicleRegistration 表格中查询文档的修订历史记录。

若要查看修订历史记录

编译并运行 query_history.py 程序，以使用 VIN 1N4AL11D75C109151查询VehicleRegistration文档的修订历史记录。

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.')

注意

您可以通过以下语法查询内置版本，以查看文档历史记录函数的修订历史记录。


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

开始时间和结束时间均为可选。它们是 Amazon Ion 的字面值，可以用反引号 (`...`) 表示。要了解更多信息，请参阅在 Amazon QLDB 中使用 PartiQL 查询 Ion。
最佳做法是，使用日期范围（开始时间 和 结束时间）和文档 ID (metadata.id) 来限定历史记录查询。QLDB 处理事务中的SELECT查询，这些查询受事务超时限制的约束。

QLDB 历史记录按文档 ID 编制索引，目前无法创建其他历史索引。包含开始时间和结束时间的历史记录查询将从日期范围限定中获得便利。

要运行该程序，请输入以下命令。
```
python query_history.py
```

要以加密方式验证 vehicle-registration 分类账中的文档修订版，请继续第 7 步：验证分类账中的文档。

Javascript 在您的浏览器中被禁用或不可用。

要使用 Amazon Web Services 文档，必须启用 Javascript。请参阅浏览器的帮助页面以了解相关说明。

文档惯例

第 5 步：修改文档

第 7 步：验证文档