dumpdata --natural-primary --natural-foreign not serializing pointers to parents in multi-table inheritance

João Sampaio

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Sep 10, 2016, 10:32:01 AM9/10/16

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Hello!

I have these classes:

class SuperClassManager(models.Manager):
    def get_by_natural_key(self, identifier):
        return self.get(identifier=identifier)


class SuperClass(models.Model):
    objects = SuperClassManager()

    identifier = models.CharField(max_length=31, unique=True)

    def natural_key(self):
        return (self.identifier, )


class SubClass(SuperClass):
    pass


class SubClassTwo(SuperClass):
    pass

When I do

./manage.py dumpdata --natural-foreign --natural-primary --indent 4 app

I get:

[
{
    "model": "app.superclass",
    "fields": {
        "identifier": "one",
    }
},
{
    "model": "app.superclass",
    "fields": {
        "identifier": "two",
    }
},
{
    "model": "app.subclass",
    "fields": {}
},
{
    "model": "app.subclasstwo",
    "fields": {}
}
]

The problem is: superclass of identifier one is a subclass or a subclasstwo? There's no way to tell. Shouldn't the output be

[
{
    "model": "app.superclass",
    "fields": {
        "identifier": "one",
    }
},
{
    "model": "app.superclass",
    "fields": {
        "identifier": "two",
    }
},
{
    "model": "app.subclass",
    "fields": {
        "superclass_ptr": [
            "one"
        ]
    }
},
{
    "model": "app.subclasstwo",
    "fields": {
        "superclass_ptr": [
            "two"
        ]
    }
}
]

Now you can tell that superclass of identifier "two" is actually a subclasstwo!

Now, I did the homework. I digged into the code. :-)

Happens that OneToOneFields that are parent_links are marked as serialize=False, so they never get serialized! Even if you create the field manually in the model, if will still be marked as serialize=False.

Shouldn't OneToOneFields that point to parents in multi-table inheritance be serialized? Otherwise, how can you tell which subclass is the superclass in the serialized output?

What do you think? Do you think this is an issue to be resolved and, if so, can I submit a pull request?

Thanks.

charettes

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Sep 10, 2016, 10:56:49 AM9/10/16

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Hi João,

It seems like this is an already reported bug[1] with an existing stale PR[2]
you might want to work on.

Cheers,
Simon

[1] https://code.djangoproject.com/ticket/24607
[2] https://github.com/django/django/pull/4473

João Sampaio

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Sep 10, 2016, 11:04:28 AM9/10/16

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Great! I've been wanting to contribute to Django for a long time, so I'll take a shot at this, hopefully I can help.

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João Sampaio

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Sep 11, 2016, 8:48:19 AM9/11/16

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Hello.

I just sent a pull request for this bug, you can check it out here: https://github.com/django/django/pull/7231

This is the first pull request I ever sent to a project, so I'm pretty excited. If there's something to fix in the pull request, let me know! There's a test to catch a regression and it's passing now.

Also, is there any chance we can backport this to 1.10.2? I think this bug is critical because it causes loss of data if someone is exporting their database using dumpdata.

Thanks!

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