Django - Are model save() methods lazy?

问题

Are model save() methods lazy in django?

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)

回答1:

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.

From the django source:

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

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

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

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.
    """
    ...

---

P.S. All line numbers apply to django version (1, 3, 0, 'alpha', 0).

来源：https://stackoverflow.com/questions/3212988/django-are-model-save-methods-lazy