Python 如何使用moto模拟DynamoDB分页？

我正在测试一些dynamodb访问代码。在过去，对分页的不正确处理会导致错误（开发人员倾向于使用少量数据手动测试，因此很容易对分页的工作方式做出错误的假设，这些假设只有在处理实际数据量时才会暴露出来）

我通常使用普通的

unittest

和

unittest.mock

对访问代码进行单元测试，并以这种方式测试分页，但我最终编写了一些相当复杂的测试代码来模拟不同操作（扫描、查询、批处理获取项目）的分页

我正在寻找一种更简单的测试方法；moto带来了一些希望

然而，我并不想将1MB+的数据加载到moto中以诱导分页，我想强制它对少量数据进行分页

所以我要问的关键是：

• moto支持DynamoDB分页吗
• 我可以配置分页阈值吗
• 怎么做
参考资料
moto是否支持DynamoDB分页？
是的，它是通过moto.mock_dynamodb2功能实现的。我已经尝试使用PynamoDB的

查询

功能进行分页，它在我的模拟DynamoDB环境中运行良好，该环境由

moto.mock_dynamodb2

提供
我可以配置分页阈值吗？
通过使用PynamoDB的

查询

，您可以在

限制

参数中对其进行配置
分页具有以下核心概念：

• hash\u-key

  +

  range\u-key\u-condition

  +

  filter\u-condition

• 要分页的DynamoDB记录列表

• 限制

• 查询返回的最大结果数

• 向前扫描索引

• 结果的顺序。您希望获取的记录按范围键/排序键按升序（例如1、2、3）或降序（例如3、2、1）排序

• last\u evaluated\u key

• 这表示数据库中最后处理的项（对于密钥）。这会将该项标记为将获取下一组项的引用点。None表示从已排序记录的开头进行查询。否则，从指定的键开始查询
• 把这想象成对

  [0,5,10,15,20,25,30,35,40,45,50]

  的二进制搜索。如果我们从一开始就对4个项目进行分页，我们将得到

  [0,5,10,15]

  。如果我们想要获得接下来的4项，我们不需要从开始（

  0

  ）到目标（

  20

  ）一直迭代。这种算法在最坏情况下会导致线性O（n）时间复杂度，其中n是所有记录的计数。相反，我们所能做的是对第一个大于最后一个取回的项（即

  15

  ）的项执行二进制搜索，在这里我们将得到

  20

  ，仅为对数O（log（n））
怎么做？
请参阅Python代码片段

# Testing date: 2020 9September 29

# Versions
# moto==1.3.16
# pynamodb==4.3.3
# pytest==6.1.0

import itertools

from moto import mock_dynamodb2
from pynamodb.attributes import *
from pynamodb.models import Model
import pytest


# Model

class Location(Model):
    class Meta:
        table_name = 'Location-table'
        region = 'ap-southeast-1'

    continent = UnicodeAttribute(hash_key=True)  # also known as partition_key
    country = UnicodeAttribute(range_key=True)  # also known as sort_key
    capital = UnicodeAttribute()
    gmt = NumberAttribute()

    def __iter__(self):
        for name, attr in self.get_attributes().items():
            yield name, attr.serialize(getattr(self, name))


# Test data

LOCATIONS = [
    {
        'continent': 'Europe',
        'country': 'Spain',
        'capital': 'Madrid',
        'gmt': 2,
    },
    {
        'continent': 'Europe',
        'country': 'Germany',
        'capital': 'Berlin',
        'gmt': 2,
    },
    {
        'continent': 'South America',
        'country': 'Venezuela',
        'capital': 'Caracas',
        'gmt': -4,
    },
    {
        'continent': 'Europe',
        'country': 'Ukraine',
        'capital': 'Kyiv',
        'gmt': 3,
    },
    {
        'continent': 'South America',
        'country': 'Brazil',
        'capital': 'Brasília',
        'gmt': -3,
    },
    {
        'continent': 'Europe',
        'country': 'Finland',
        'capital': 'Helsinki',
        'gmt': 3,
    },
    {
        'continent': 'Europe',
        'country': 'Ireland',
        'capital': 'Dublin',
        'gmt': 1,
    },
]


# Test algorithms

def _setup_table(locations):
    Location.create_table()

    for location in locations:
        Location(**location).save()

def _get_filter_condition():
    # Put logic here for the filter condition. Uncomment the code below to try.
    # filter_condition = (Location.gmt >= 2) \
    #                     & (Location.capital.contains('in') | Location.capital.startswith('A'))
    # return filter_condition
    return None


@mock_dynamodb2
def test_dynamodb_pagination():
    _setup_table(LOCATIONS)
    filter_condition = _get_filter_condition()

    # Expected query order for Europe. This should be sorted by country (which is the sort_key field).
    SORTED_EUROPE_COUNTRIES = [
        'Finland',
        'Germany',
        'Ireland',
        'Spain',
        'Ukraine',
    ]
    country_index = 0

    # This indicates the last processed item (for the key) from the database. This marks that item
    # as the reference point to where the next set of items will be fetched. None means query from
    # the beginning of the sorted records. Otherwise, start the query from the indicated key.
    last_evaluated_key = None

    for query_index in itertools.count(0):
        result = Location.query(
            hash_key='Europe',
            filter_condition=filter_condition,  # Filter the query results
            limit=2,  # Maximum number of items to fetch from the database
            last_evaluated_key=last_evaluated_key,  # The reference starting point of the fetch
            scan_index_forward=True,  # Indicate if in lexicographical order (increasing) or in reverse (decreasing)
        )

        for item in result:
            print(f"Query #{query_index} - Country #{country_index} - {item}")

            assert item.country == SORTED_EUROPE_COUNTRIES[country_index]
            country_index += 1

        print(f"result.last_evaluated_key {result.last_evaluated_key}\n")
        last_evaluated_key = result.last_evaluated_key

        if last_evaluated_key is None:
            print(f"Reached the last queried item in the database")
            break

输出：

(venv) nponcian 2020_9Sep_10_DynamoDB$ pytest pagination_test.py -rP
====================================================================================== test session starts ======================================================================================
platform linux -- Python 3.8.2, pytest-6.1.0, py-1.9.0, pluggy-0.13.1
rootdir: /home/nponcian/Documents/Program/2020_9Sep_10_DynamoDB
plugins: cov-2.10.1, mock-3.3.1
collected 1 item                                                                                                                                                                                

pagination_test.py .                                                                                                                                                                      [100%]

============================================================================================ PASSES =============================================================================================
___________________________________________________________________________________ test_dynamodb_pagination ____________________________________________________________________________________
------------------------------------------------------------------------------------- Captured stdout call --------------------------------------------------------------------------------------
Query #0 - Country #0 - Location-table<Europe, Finland>
Query #0 - Country #1 - Location-table<Europe, Germany>
result.last_evaluated_key {'continent': {'S': 'Europe'}, 'country': {'S': 'Germany'}}

Query #1 - Country #2 - Location-table<Europe, Ireland>
Query #1 - Country #3 - Location-table<Europe, Spain>
result.last_evaluated_key {'continent': {'S': 'Europe'}, 'country': {'S': 'Spain'}}

Query #2 - Country #4 - Location-table<Europe, Ukraine>
result.last_evaluated_key None

Reached the last queried item in the database
======================================================================================= 1 passed in 0.40s =======================================================================================

（venv）NPOCIAN 2020年9月10日发电机$pytest分页\u test.py-rP
====================================================================================================================================测试会话开始======================================================================================
平台linux——Python 3.8.2、pytest-6.1.0、py-1.9.0、pluggy-0.13.1
rootdir:/home/npocian/Documents/Program/2020\u 9Sep\u 10\u DynamoDB
插件：cov-2.10.1，mock-3.3.1
收集1项
分页_test.py。[100%]
=========================================================================================================================================================通行证=============================================================================================
___________________________________________________________________________________测试发电机分页____________________________________________________________________________________
-------------------------------------------------------------------------------------捕获的stdout调用--------------------------------------------------------------------------------------
查询#0-国家#0-位置表
查询#0-国家#1-位置表
result.last_评估了_key{‘大陆’：{‘欧洲’}，‘国家’：{‘德国’}
查询#1-国家#2-位置表
查询#1-国家#3-位置表
result.last_评估_key{‘大陆’：{‘欧洲’}，‘国家’：{‘西班牙’}
查询#2-国家#4-位置表
结果。最后一次评估\u键无
已到达数据库中最后查询的项
=================================================================================================================================================1在0.40秒内通过=======================================================================================