python - 为什么添加这个 __init__() 方法会破坏我的 Django 模型？

Question

这个问题是我之前提出的问题的后续问题 here .

我有一个 Django 模型，如下所示:

class MyModel(models.Model):
    my_field1 = models.DateTimeField(default=datetime.utcnow, editable=False)
    my_field2 = models.DateTimeField()

它有效:

>>> MyModel.objects.all()
[<MyModel: MyModel object>, <MyModel: MyModel object>,

现在我将以下构造函数添加到 MyModel:

def __init__(self, **kwargs):
    super(MyModel, self).__init__(**kwargs)
    if self.my_field2 is None:
        self.my_field2 = self.my_field1

这打破了类(Class):

>>> MyModel.objects.all()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "MYvirtualenv/lib/python2.7/site-packages/django/db/models/query.py", line 138, in __repr__
    data = list(self[:REPR_OUTPUT_SIZE + 1])
  File "MYvirtualenv/lib/python2.7/site-packages/django/db/models/query.py", line 162, in __iter__
    self._fetch_all()
  File "MYvirtualenv/lib/python2.7/site-packages/django/db/models/query.py", line 965, in _fetch_all
    self._result_cache = list(self.iterator())
  File "MYvirtualenv/src/django-cache-machine-master/caching/base.py", line 118, in __iter__
    obj = iterator.next()
  File "MYvirtualenv/lib/python2.7/site-packages/django/db/models/query.py", line 255, in iterator
    obj = model_cls.from_db(db, init_list, row[model_fields_start:model_fields_end])
  File "MYvirtualenv/lib/python2.7/site-packages/django/db/models/base.py", line 489, in from_db
    new = cls(*values)
TypeError: __init__() takes exactly 1 argument (2 given)

为什么当我添加相对简单的构造函数时会发生这种情况？我该如何补救呢？我需要该构造函数中的逻辑，所以我不能直接消除它。

Answer 1

尽管强烈建议您在文档中使用类方法或自定义管理器，但您的代码将无法工作，因为您修改了父类(super class)的调用签名>，应该是:

super(MyModel, self).__init__(*args, **kwargs)

您可以通过使用类方法来避免这样做:

class MyModel(models.Model):
    my_field1 = models.DateTimeField(default=datetime.utcnow, editable=False)
    my_field2 = models.DateTimeField()

    @classmethod
    def sync_dates(cls, myfield1):
         my_model = cls(my_field1=myfield1, my_field2=myfield1)
         # do something with my_model
         return my_model

MyModel.sync_dates(some_date) 就可以了。

或者您可以使用自定义管理器，这是首选方式:

class MyModelManager(models.Manager):
    def create_with_sync_date(self, myfield1):
        my_model = self.create(my_field1=myfield1, my_field2=myfield1)
        # do something with my_model
        return my_model

class MyModel(models.Model):
    my_field1 = models.DateTimeField(default=datetime.utcnow, editable=False)
    my_field2 = models.DateTimeField()

    objects_synced = MyModelManager()

您可以调用MyModel.objects_synced.create_with_sync_date(some_date)