我正在测试一些 dynamodb 访问代码。在过去，不正确的分页处理会导致错误（开发人员倾向于使用少量数据进行手动测试，因此很容易对分页的工作方式做出错误的假设，只有在处理实际数据量时才会显现出来）
我通常使用纯 unittest 和 unittest.mock 对访问代码进行单元测试，并以这种方式测试了分页，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的分页（扫描、查询，batch_get_item)。
我正在寻找一种更简单的测试方法； moto 带来了一些希望
但是，我真的不想将 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：
【问题讨论】：
标签： python amazon-web-services pagination amazon-dynamodb moto
参考文献
moto 是否支持 DynamoDB 分页？
是的，它通过moto.mock_dynamodb2 功能实现。我尝试使用 PynamoDB 的 query 功能进行分页，它在 moto.mock_dynamodb2 提供的模拟 DynamoDB 环境中运行良好。
我可以配置分页阈值吗？
通过使用PynamoDB的query，可以在limit参数中进行配置。
分页有这个核心概念：
hash_key + range_key_condition + filter_condition
limitscan_index_forwardlast_evaluated_key[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50] 的二分搜索。如果我们从一开始就对 4 个项目进行分页，我们会得到 [0, 5, 10, 15]。如果我们想获得接下来的 4 个项目，我们不需要从开始（0）一直迭代到目标（20 向前）。这种算法在最坏的情况下会导致线性 O(n) 时间复杂度，其中 n 是所有记录的计数。相反，我们可以做的是对大于最后一个获取的项目（15）的第一个项目执行二进制搜索，我们将在对数 O(log(n)) 中得到 20。李>
怎么做？
查看 Python 代码 sn-p
# 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 =======================================================================================
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