怎么利用djangomodelsave方法对未更改的字段进行保存-创新互联
小编给大家分享一下怎么利用django model save方法对未更改的字段进行保存，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
直接上代码吧！
obj = Obj.objects.get(id=1) print obj.name #此时name的值假定为'abc' def handler(oid): obj = Obj.objects.get(id=oid) obj.name = '123' obj.save() handler(obj.id) obj.age = 10 obj.save() print obj.name
最终的name结果依然为'abc'。save()保存时,虽然没有更改其它字段，但依然会将内存中的值，再次存入数据库，子函数和其它进程更改的值会被覆盖。
补充知识：Django Signals之pre_save & post_save ，pre_delete & post_delete
Listening to signals（信号监听）
To receive a signal, register a receiver function using the Signal.connect() method. The receiver function is called when the signal is sent.
（为了接收信号，需要使用Signal.connect()方法注册一个接收器函数，当信号发送后接收器函数就会被调用）
Signal.connect(receiver, sender=None, weak=True, dispatch_uid=None)[source]
Parameters: 参数解析
receiver – The callback function which will be connected to this signal. See Receiver functions for more information.
sender – Specifies a particular sender to receive signals from. See Connecting to signals sent by specific senders for more information.
weak – Django stores signal handlers as weak references by default. Thus, if your receiver is a local function, it may be garbage collected. To prevent this, pass weak=False when you call the signal's connect() method.
dispatch_uid – A unique identifier for a signal receiver in cases where duplicate signals may be sent. See Preventing duplicate signals for more information.
一般使用是这样的：
def my_callback(sender, **kwargs):
print("Request finished!")
#Connecting receiver functions（连接接收器函数）
#There are two ways you can connect a receiver to a signal. You can take the manual connect route:
from django.core.signals import request_finished
request_finished.connect(my_callback)当然，喜欢装逼（高技术）的人喜欢使用另外一种方式，receiver()装饰器：
receiver(signal)[source]#用法
Parameters: signal – A signal or a list of signals to connect a function to.
下面将针对本文标题来做示例：
django.db.models.signals.pre_save & django.db.models.signals.post_save
Sent before or after a model's save() method is called.
在模型保存操作执行前或者执行后发送信号
Connecting to signals sent by specific senders
（连接到特定发送器发送的信号）
Some signals get sent many times, but you'll only be interested in receiving a certain subset of those signals. For example, consider the django.db.models.signals.pre_save signal sent before a model gets saved. Most of the time, you don't need to know when any model gets saved – just when one specific model is saved.
（有些信号会被多次发送，但是我们通常只是对其中的一些信号子集感兴趣，下面将演示针对具体的某个模型的pre_save以及post_save来发送信号）
从上边的运行结果可以看出，两个函数都被执行了，但是是有一定的执行顺序的，pre then post
In these cases, you can register to receive signals sent only by particular senders. In the case of django.db.models.signals.pre_save, the sender will be the model class being saved, so you can indicate that you only want signals sent by some model:
django.db.models.signals.pre_delete & django.db.models.signals.post_delete
Sent before or after a model's delete() method or queryset's delete() method is called.
在模型删除操作执行前或者执行后发送信号
下面将演示pre_delete与post_delete这两个模型信号的使用
和save的运行逻辑一样，pre信号先触发，post后触发
以上是“怎么利用django model save方法对未更改的字段进行保存”这篇文章的所有内容，感谢各位的阅读！相信大家都有了一定的了解，希望分享的内容对大家有所帮助，如果还想学习更多知识，欢迎关注创新互联成都网站设计公司行业资讯频道！
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