Django - 是模型save（）方法懒吗？

问题描述：

是django中的模型save（）方法吗？

Are model save() methods lazy in django?

例如，下面的代码示例中的什么行将django命中数据库？

For instance, at what line in the following code sample will django hit the database?

my_model = MyModel()
my_model.name = 'Jeff Atwood'
my_model.save()
# Some code that is independent of my_model...
model_id = model_instance.id
print (model_id)

答

有一个延迟保存没有什么意义，是吗？ Django的 QuerySets 是懒惰的，模型的 save 方法不是。

It does not make much sense to have a lazy save, does it? Django's QuerySets are lazy, the model's save method is not.

从django源：

django / db / models / base.py ，第424-437行：

django/db/models/base.py, lines 424–437:

def save(self, force_insert=False, force_update=False, using=None):
    """
    Saves the current instance. Override this in a subclass if you want to
    control the saving process.

    The 'force_insert' and 'force_update' parameters can be used to insist
    that the "save" must be an SQL insert or update (or equivalent for
    non-SQL backends), respectively. Normally, they should not be set.
    """
    if force_insert and force_update:
        raise ValueError("Cannot force both insert and updating in \
            model saving.")
    self.save_base(using=using, force_insert=force_insert, 
        force_update=force_update)

save.alters_data = True

然后， save_base 执行重载（同一文件，行号439-545）：

Then, save_base does the heavy lifting (same file, lines 439–545):

...
transaction.commit_unless_managed(using=using)
...

并且在 django /db/transaction.py ，第167-178行，您会发现：

And in django/db/transaction.py, lines 167–178, you'll find:

def commit_unless_managed(using=None):
    """
    Commits changes if the system is not in managed transaction mode.
    """
    ...

$ b b

PS所有行号适用于django版本（1，3，0，'alpha'，0）。

Django - 是模型save（）方法懒吗？

相关推荐