Question

django中的模型save（）方法是否很懒惰？

例如，以下代码示例中的哪一行将django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)

Answer 1

懒惰保存没有多大意义，是吗？ Django的QuerySets是懒惰的，模型的save方法不是。

来自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执行繁重的工作（相同的文件，第439-545行）：

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

在django/db/transaction.py第167-178行，你会发现：

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

P.S。所有行号都适用于django版本(1, 3, 0, 'alpha', 0)。

Django - 模型save（）方法是否懒惰？

1 个答案: