[Python] How to add a relationship to a GeneratedField in Django

Context


I have a model:

class Article(models.Model):
id = models.UUIDField(default=uuid4, editable=False, unique=True, primary_key=True)
paper_id: UUID | None
paper = models.ForeignKey["Paper"](
"Paper",
on_delete=models.CASCADE,
related_name="articles",
null=True,
blank=True,
)
website_id: UUID | None
website = models.ForeignKey["Website"](
"Website",
on_delete=models.CASCADE,
related_name="articles",
null=True,
blank=True,
)


I then have a view that unifies Paper and Website:

class Source(pg.View):
sql = """
SELECT ...
FROM papers

UNION ALL

SELECT ...
FROM websites
;
"""

id = models.UUIDField(unique=True, primary_key=True)

# ...


Question


I'd like to make it so from a Source model I can get the articles (e.g. source.articles.all()). How can I do that?

What have I tried?


I've tried to add this field to Article:

source_id = models.GeneratedField(
expression=Coalesce(F("paper_id"), F("website_id")),
output_field=models.UUIDField(),
db_persist=False,
)
source = models.ForeignKey["Source"](
"Source",
on_delete=models.DO_NOTHING,
related_name="articles",
db_column="source_id",
to_field="id",
null=True,
editable=False,
)


But when creating the migration I get:

(models.E006) The field 'source' clashes with the field 'source_id' from model 'Article'.
​

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