Tortoise-orm信号实现及使用场景源码详解
场景
源码
看看在模型save的时候，都干了什么？
自己实现一个信号
总结
场景在使用Tortoise操作数据库的时候发现，通过对操作数据库模型加以装饰器，如@pre_save(Model)，可以实现对这个模型在savue时，自动调用被装饰的方法，从而实现对模型的一些操作。
在此先从官方文档入手，看一下官方的对于模型信号的Example
# -*- coding: utf-8 -*-
"""
This example demonstrates model signals usage
"""
from typing import List, Optional, Type
from tortoise import BaseDBAsyncClient, Tortoise, fields, run_async
from tortoise.models import Model
from tortoise.signals import post_delete, post_save, pre_delete, pre_save
class Signal(Model):
id = fields.IntField(pk=True)
name = fields.TextField()
class Meta:
table = "signal"
def __str__(self):
return self.name
@pre_save(Signal)
async def signal_pre_save(
sender: "Type[Signal]", instance: Signal, using_db, update_fields
) -> None:
print('signal_pre_save', sender, instance, using_db, update_fields)
@post_save(Signal)
async def signal_post_save(
sender: "Type[Signal]",
instance: Signal,
created: bool,
using_db: "Optional[BaseDBAsyncClient]",
update_fields: List[str],
) -> None:
print('post_save', sender, instance, using_db, created, update_fields)
@pre_delete(Signal)
async def signal_pre_delete(
sender: "Type[Signal]", instance: Signal, using_db: "Optional[BaseDBAsyncClient]"
) -> None:
print('pre_delete', sender, instance, using_db)
@post_delete(Signal)
async def signal_post_delete(
sender: "Type[Signal]", instance: Signal, using_db: "Optional[BaseDBAsyncClient]"
) -> None:
print('post_delete', sender, instance, using_db)
async def run():
await Tortoise.init(db_url="sqlite://:memory:", modules={"models": ["__main__"]})
await Tortoise.generate_schemas()
# pre_save,post_save will be send
signal = await Signal.create(name="Signal")
signal.name = "Signal_Save"
# pre_save,post_save will be send
await signal.save(update_fields=["name"])
# pre_delete,post_delete will be send
await signal.delete()
if __name__ == "__main__":
run_async(run())
以上代码可直接复制后运行，运行后的结果：
signal_pre_save <class '__main__.Signal'> Signal <tortoise.backends.sqlite.client.SqliteClient object at 0x7f8518319400> None
post_save <class '__main__.Signal'> Signal <tortoise.backends.sqlite.client.SqliteClient object at 0x7f8518319400> True None
signal_pre_save <class '__main__.Signal'> Signal_Save <tortoise.backends.sqlite.client.SqliteClient object at 0x7f8518319400> ['name']
post_save <class '__main__.Signal'> Signal_Save <tortoise.backends.sqlite.client.SqliteClient object at 0x7f8518319400> False ['name']
pre_delete <class '__main__.Signal'> Signal_Save <tortoise.backends.sqlite.client.SqliteClient object at 0x7f8518319400>
post_delete <class '__main__.Signal'> Signal_Save <tortoise.backends.sqlite.client.SqliteClient object at 0x7f8518319400>
可以发现，对模型进行保存和删除时候，都会调用对应的信号方法。
源码从导包可以得知，tortoise的所有信号方法都在tortoise.signals中。
from enum import Enum
from typing import Callable
Signals = Enum("Signals", ["pre_save", "post_save", "pre_delete", "post_delete"])
def post_save(*senders) -> Callable:
"""
Register given models post_save signal.
:param senders: Model class
"""
def decorator(f):
for sender in senders:
sender.register_listener(Signals.post_save, f)
return f
return decorator
def pre_save(*senders) -> Callable:
...
def pre_delete(*senders) -> Callable:
...
def post_delete(*senders) -> Callable:
...
其内部实现的四个信号方法分别是模型的保存后，保存前，删除前，删除后。
其内部装饰器代码也十分简单，就是对装饰器中的参数（也就是模型），注册一个监听者，而这个监听者，其实就是被装饰的方法。
如上面的官方示例中：
# 给模型Signal注册一个监听者，它是方法signal_pre_save
@pre_save(Signal)
async def signal_pre_save(
sender: "Type[Signal]", instance: Signal, using_db, update_fields
) -> None:
print('signal_pre_save', sender, instance, using_db, update_fields)
而到了Model类中，自然就有一个register_listener方法，定睛一看，上面示例Signal中并没有register_listener方法，所以自然就想到了，这个方法必定在父类Model中。
class Model:
...
@classmethod
def register_listener(cls, signal: Signals, listener: Callable):
...
if not callable(listener):
raise ConfigurationError("Signal listener must be callable!")
# 检测是否已经注册过
cls_listeners = cls._listeners.get(signal).setdefault(cls, []) # type:ignore
if listener not in cls_listeners:
# 注册监听者
cls_listeners.append(listener)
接下来注册后，这个listeners就会一直跟着这个Signal类。只需要在需要操作关键代码的地方，进行调用即可。
看看在模型save的时候，都干了什么？ async def save(
self,
using_db: Optional[BaseDBAsyncClient] = None,
update_fields: Optional[Iterable[str]] = None,
force_create: bool = False,
force_update: bool = False,
) -> None:
...
# 执行保存前的信号
await self._pre_save(db, update_fields)
if force_create:
await executor.execute_insert(self)
created = True
elif force_update:
rows = await executor.execute_update(self, update_fields)
if rows == 0:
raise IntegrityError(f"Can't update object that doesn't exist. PK: {self.pk}")
created = False
else:
if self._saved_in_db or update_fields:
if self.pk is None:
await executor.execute_insert(self)
created = True
else:
await executor.execute_update(self, update_fields)
created = False
else:
# TODO: Do a merge/upsert operation here instead. Let the executor determine an optimal strategy for each DB engine.
await executor.execute_insert(self)
created = True
self._saved_in_db = True
# 执行保存后的信号
await self._post_save(db, created, update_fields)
抛开其他代码，可以看到，在模型save的时候，其实是先执行保存前的信号，然后执行保存后的信号。
自己实现一个信号有了以上的经验，可以自己实现一个信号，比如我打算做个数据处理器的类，我想在这个处理器工作中，监听处理前/后的信号。
# -*- coding: utf-8 -*-
from enum import Enum
from typing import Callable, Dict
# 声明枚举信号量
Signals = Enum("Signals", ["before_process", "after_process"])
# 处理前的装饰器
def before_process(*senders):
def decorator(f):
for sender in senders:
sender.register_listener(Signals.before_process, f)
return f
return decorator
# 处理后的装饰器
def after_process(*senders):
def decorator(f):
for sender in senders:
sender.register_listener(Signals.after_process, f)
return f
return decorator
class Model(object):
_listeners: Dict = {
Signals.before_process: {},
Signals.after_process: {}
}
@classmethod
def register_listener(cls, signal: Signals, listener: Callable):
"""注册监听者"""
# 判断是否已经存在监听者
cls_listeners = cls._listeners.get(signal).setdefault(cls, [])
if listener not in cls_listeners:
# 如果不存在，则添加监听者
cls_listeners.append(listener)
def _before_process(self):
# 取出before_process监听者
cls_listeners = self._listeners.get(Signals.before_process, {}).get(self.__class__, [])
for listener in cls_listeners:
# 调用监听者
listener(self.__class__, self)
def _after_process(self):
# 取出after_process监听者
cls_listeners = self._listeners.get(Signals.after_process, {}).get(self.__class__, [])
for listener in cls_listeners:
# 调用监听者
listener(self.__class__, self)
class SignalModel(Model):
def process(self):
"""真正的调用端"""
self._before_process()
print("Processing")
self._after_process()
# 注册before_process信号
@before_process(SignalModel)
def before_process_listener(*args, **kwargs):
print("before_process_listener1", args, kwargs)
# 注册before_process信号
@before_process(SignalModel)
def before_process_listener(*args, **kwargs):
print("before_process_listener2", args, kwargs)
# 注册after_process信号
@after_process(SignalModel)
def before_process_listener(*args, **kwargs):
print("after_process_listener", args, kwargs)
if __name__ == '__main__':
sm = SignalModel()
sm.process()
输出结果：
总结before_process_listener1 (<class '__main__.SignalModel'>, <__main__.SignalModel object at 0x7ff700116e50>) {}
before_process_listener2 (<class '__main__.SignalModel'>, <__main__.SignalModel object at 0x7ff700116e50>) {}
Processing
after_process_listener (<class '__main__.SignalModel'>, <__main__.SignalModel object at 0x7ff700116e50>) {}
笔者通过对`tortoise-orm`源码的学习，抽丝剥茧，提取了信号实现的方式。其核心就是通过一个字典存储调用方自定义的process方法，然后分别在真正的调用端的前/后触发这些自定义方法即可。
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