database - Django-模型save()方法是否懒惰？

模型save()方法在django中是懒惰的吗？

例如，在以下代码示例的哪一行，django将命中数据库？

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)

最佳答案

懒惰的保存没有多大意义，对吗？ Django的 QuerySets 是惰性的，模型的save方法不是。

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

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进行繁重的工作(同一文件，第439–545行):

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

在django/db/transaction.py的第167-178行中，您将找到:

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

P.S.所有行号均适用于Django版本(1, 3, 0, 'alpha', 0)。

关于database - Django-模型save()方法是否懒惰？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/3212988/