Two step object creation in Django Admin - django

Question

I'm trying to change the implementation of an EAV model using a JSONField to store all the attributes defined by an attribute_set.
I already figured out how to build a form to edit the single attributes of the JSON, but I'm currently stuck at implementing the creation of a new object. I think I have to split object creation in two steps, because I need to know the attribute_set to generate the correct form, but I don't know if there's a way to hook in the create action, or any other way to achieve what I need.
My models look like this:
class EavAttribute(models.Model):
entity_type = models.CharField(max_length=25, choices=entity_types)
code = models.CharField(max_length=30)
name = models.CharField(max_length=50)
data_type = models.CharField(max_length=30, choices=data_types)
class AttributeSet(models.Model):
name = models.CharField(max_length=25)
attributes = models.ManyToManyField('EavAttribute')
class EntityAbstract(models.Model):
attribute_set = models.ForeignKey(
'AttributeSet',
blank=False,
null=False,
unique=False,
)
class Meta:
abstract = True
class Event(EntityAbstract):
entity_type = models.CharField(max_length=20, null=False, choices=entity_types, default=DEFAULT_ENTITY_TYPE)
code = models.CharField(max_length=25, null=True, blank=True, db_index=True)
year = models.IntegerField(db_index=True)
begin_date = models.DateField()
end_date = models.DateField()
data = JSONField()
How can I choose the AttributeSet first and then go to another form that I would populate with the attributes in the chosen attribute set?

Answer 1

I ended up using get_fields() and response_add() methods, like so:
def get_fields(self, request, obj=None):
if obj is None:
return ['attribute_set']
else:
return [attr.name for attr in obj._meta.get_fields() if not attr.auto_created and attr.name != 'id']
def get_readonly_fields(self, request, obj=None):
readonly_fields = ['entity_type', 'code', 'state']
if obj is not None:
readonly_fields.append('attribute_set')
return readonly_fields
def response_add(self, request, obj, post_url_continue=None):
url = '/admin/risks/event/{}/change/'.format(obj.id)
return redirect(url)
The downside of this approach is that object is saved in the database and then opened for edit, so basically the database is hit twice and all attributes have to be nullable, except for attribute_set.
I would be happy to receive ideas for better implementations.