确保缓存queryset

我相信你正在寻求的解决方案是 memoization 的 get_rules_that_applies 方法

有一种现成的工具,叫做 django-memoize 和 those 是它的文档。

1. pip install django-memoize

2. INSTALLED_APPS

   INSTALLED_APPS = [
       '...',
       'memoize',
   ]
   

3. 在你的 model.py

   from memoize import memoize
   
   class Rule(models.Model):
       warehouse = models.ForeignKey('Warehouse')
       categories1 = models.ManyToManyField('Category1')
       categories2 = models.ManyToManyField('Category2')
       categories3 = models.ManyToManyField('Category3')
   
       @staticmethod
       @memoize(timeout=something_reasonable_in_seconds)
       def get_rules_that_applies(item):
           rules = warehouse.rule_set.all()
           if not rules.exists():
               return None
              # ... determine which rule applies to the item by filtering, etc.
           return rules
   

从我的回答开始,我读了以下帖子: https://www.peterbe.com/plog/cache_memoize-cache-decorator-for-django gist 关于如何实现自我记忆。

Python 3.2及更高版本:

@functools.lru_cache 装饰师是:

Decorator将函数包装为一个可记忆的可调用函数,该函数最多可保存最大大小的最近调用。当使用相同的参数定期调用昂贵的函数或I/O绑定函数时,它可以节省时间。

如何使用:

from functools import lru_cache


class Rule(models.Model):
    ...

    @lru_cache(maxsize=a_reasonable_integer_size_of_cache)
    def get_rules_that_applies(item):
        rules = warehouse.rule_set.all()
        if not rules.exists():
            return None
            # ... determine which rule applies to the item by filtering, etc.
        return rules

maxsize :定义要存储的函数调用中缓存的大小。它可以设置为 None

Python<3.2

在这里 What is memoization and how can I use it in Python?

如何使用上述任一方法缓存查询集:

为什么不定义一个中间函数来形成函数结果的查询集和缓存?

@lru_cache(maxsize=None)

or 

@memoize()
def middle_function():
    return warehouse.rule_set.all()

然后在你的 功能:

def get_rules_that_applies(item):
    rules = middle_function()

您有2种选择:

1. 在视图中缓存项目
2. 计算模型中的项目

from django.core.cache import cache

代码:

if cache.get('query_result') is not None:
    return cache.get('query_result')
else:
    cache.set('query_result', result, 3600)
    #cache.set('cache_name', 'your query', 'expiry time')
    return rule

您的模型将是:

class Rule(models.Model):
warehouse = models.ForeignKey('Warehouse')
categories1 = models.ManyToManyField('Category1')
categories2 = models.ManyToManyField('Category2')
categories3 = models.ManyToManyField('Category3')

@staticmethod
def get_rules_that_applies(item):
    rules = warehouse.rule_set.all()
    if not rules.exists():
        return None
    # ... determine which rule applies to the item by filtering, etc.
    if cache.get('query_result') is not None:
        return cache.get('query_result')
    else:
        cache.set('query_result', result, 3600)
        #cache.set('cache_name', 'your query', 'expiry time')
        return rule

    return rule

https://docs.djangoproject.com/en/1.11/ref/models/querysets/#when-querysets-are-evaluated

希望这有帮助