Dump (Export) Django data

In docs:

• /ref/django-admin.html#dumpdata

• /topics/serialization.html#topics-serialization-natural-keys

Dumping

Syntax:

django-admin dumpdata --output=outputfile.json --indent=2 [app_label[.ModelName] [app_label[.ModelName] ...]]

We generally want to use natural keys, so add:

--natural-foreign --natural-primary

And in each model, we need to add support for that.

First, add a natural_key method that returns a tuple whose value uniquely identifies the record without using the pk:

def natural_key(self):
    return (self.task.label, self.url)

Next, create a custom manager with a get_by_natural_key method that takes that tuple as *args and returns the corresponding record:

class TaskLinkManager(models.Manager):
    def get_by_natural_key(self, task_label, url):
        return self.get(task__label=task_label, url=url)


class TaskLink(models.Model):
    # ...
    objects = TaskLinkManager()

Finally, consider whether using get_by_natural_key will require that some other model be restored first. If so, we need to declare dependencies so restoration can occur in the right order. E.g.:

def natural_key(self):
    return (self.task.label, self.url)
natural_key.dependencies = ["appname.Model1", "appname.Model2"]

Compressing dumps

Dumps can be big but they compress very well and can be restored without uncompressing, e.g. with bzip2:

$ bzip2 bigdump.json
$ python manage.py loaddata bigdump.json.bz2