Hi.
I think you have a bit confused terms model inheritance and abstract models.
Normal model inheritance in Django means that there will be implicit one to
one relation to base model. Inherited model still receives all fields from
parent model. On save data is just saved to correct models. To both parent
and child. And both models do have separate tables.
If inherited model is abstract all fields are copied to inherited model and
django treats model as one. There is no parent table created but columns
are added to inheriting model table.
pe 5. heinäk. 2019 klo 20.42 Kalev Takkis <kalev.tak...@gmail.com>
kirjoitti:
> Hi all,
>
> tl;dr: saving inherited model overwrites fields in parent models with
> empty strings
>
> I have the following models:
>
> class Contact(models.Model):
> comment = models.CharField(max_length=255, blank=True)
> emails = models.ManyToManyField(
> Email,
> blank=True,
> through='ContactEmail',
> through_fields=('contact', 'email'),
> )
>
> # couple of more manytomanys, to addresses, phones, etc
>
>
> class ContactEmail(BaseContactJunctionModel):
> email = models.ForeignKey(Email, null=True, on_delete=models.SET_NULL)
> contact = models.ForeignKey(Contact, on_delete=models.CASCADE)
> event = models.ForeignKey(ContactEvent, on_delete=models.PROTECT)
> event_date = models.DateTimeField(default=timezone.now)
>
>
> # other similar through tables for the rest of the manytomanys and their
> target models
>
>
> class Organisation(Contact):
>
> name = models.CharField(max_length=255, blank=True)
> hierarchy = models.ManyToManyField(
> 'self',
> blank=True,
> symmetrical=False,
> through='OrganisationHierarchy',
> through_fields=('sender', 'target'),
> )
>
> # again, more manytomanys, not to self though
>
> # not sure this is relevant but as it's to self, then just in case
> class OrganisationHierarchy(BaseContactJunctionModel):
> # this, instance that specifies relationship
> sender = models.ForeignKey(
> Organisation,
> null=True,
> related_name='senders',
> on_delete=models.SET_NULL,
> )
>
> # instance that 'this' or 'sender' is related to
> target = models.ForeignKey(
> Organisation,
> null=True,
> related_name='targets',
> on_delete=models.SET_NULL,
> )
>
> connection_type = models.ForeignKey(
> ConnectionType,
> null=True,
> on_delete=models.PROTECT,
> )
>
> I have a view based on CreateView and a template to capture user
> input. The post request coming from browser is a-ok, saving
> emails, contact, contactemails and other manytomany targets and
> junction tables works without a problem but when getting to
> saving Organisation, this happens (pseudocode):
>
> save() is called from django/db/models/base.py
> save_base() is called with self=Organisation
> save_base calls _save_parents(self=Organisation, cls=Organisation)
> save_parents loops through cls._meta.parents and comes across
> relation
> parent=Contact, field=Organisation.contact_ptr
> calls _save_table with self=Organisation and cls=Contact
> _save_table finds from cls._meta that it has
> local concrete field "comment" and stores it in list
> non_pks
> it then finds the values for those fields like
> this:
> f.pre_save(self, false) for f in non_pks
>
> I then see a call to _update in queries.py and Contact instance
> is updated with new values.
>
> I don't really understand what's happening here, the code finds
> local concrete fields from "cls" which at this point is Contact
> and comes up, correctly, with "comment" but then it tries to
> query the field value form "self" which at this point is
> Organisation object. I'm not sure why Organisation has "comment"
> attribute at all, because the way I read the docs it should only
> happen when the base model is abstract or when the inherited
> model is proxy model, neither of which is the case. Anyway, the
> value returned by save_base for the "comment" from "self" is not
> the value I inserted into the form field (and what has previously
> been saved to Contact object) but is instead an empty string.
>
> The end result is, after Contact object is correctly saved it is,
> moments later, overwritten by an empty string. Does anybody have
> a clue as to what is happening and most importantly, how can I
> avoid it?
>
> Thanks,
>
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