SQLAlchemy 中的 cache_ok 标志是什么？

Question

我有 SQLAlchemy 的下一个自定义类型装饰器：

class TimeStamp(TypeDecorator):
    impl = DateTime
    cache_ok = True
    LOCAL_TIMEZONE = datetime.utcnow().astimezone().tzinfo

    def process_literal_param(self, value, dialect):
        return self.imple.process_literal_param(value, dialect)

    @property
    def python_type(self):
        return self.impl.python_type

    def process_bind_param(self, value: datetime, dialect):
        if value is None:
            return None
        if value.tzinfo is None:
            value = value.astimezone(self.LOCAL_TIMEZONE)
        return value.astimezone(timezone.utc)

    def process_result_value(self, value, dialect):
        if value is None:
            return None
        if value.tzinfo is None:
            return value.replace(tzinfo=timezone.utc)
        return value.astimezone(timezone.utc)

问题是 SQLAlchemy 要求我设置 cache_ok 标志...我试图在 docs 中阅读有关此标志的内容，但是我还不清楚。我不明白 SQLAlchemy 如何使用它。
它缓存了什么？我的类型装饰器适合缓存吗？

Answer 1

运行最近发现了你的问题，没有答案 :( .. 进一步查看，查看了文档 ..

The TypeDecorator.cache_ok class-level flag indicates if this custom TypeDecorator is safe to be used as part of a cache key. This flag defaults to None which will initially generate a warning when the SQL compiler attempts to generate a cache key for a statement that uses this type. If the TypeDecorator is not guaranteed to produce the same bind/result behavior and SQL generation every time, this flag should be set to False; otherwise if the class produces the same behavior each time, it may be set to True. See TypeDecorator.cache_ok for further notes on how this works.

https://docs.sqlalchemy.org/en/14/core/custom_types.html#sqlalchemy.types.TypeDecorator

.. 因此，如果您确信您的 TypeDecorator 始终为给定值生成相同的 bind/result，那么继续并通过在您的 TypeDecorator [=] 中设置值 cache_ok = True 来发出该语句20=].

SQLAlchemy 中的 cache_ok 标志是什么？

What's the cache_ok flag in SQLAlchemy?

python

sqlalchemy