Generic relations pointing to the same model

Question

I currently have a problem with generic keys. I do not know how to easily set two GenericRelation pointing to the same model as below:

Assume that we have the classes below :

class Pen(models.Model):
  color = models.CharField(choices=COLORS)

  content_type = models.ForeignKey(ContentType)
  object_id = models.PositiveIntegerField()
  item = generic.GenericForeignKey('content_type', 'object_id')

class PencilCase(models.Model):

  ballpoint_pens = generic.GenericRelation(Pen, related_name="ballpointpencil+")
  fountain_pens = generic.GenericRelation(Pen, related_name="fountainpencil+")

The problem is that Django can not do the difference between a ballpoint pen and a fountain_pen. So as expected, each pen are both in the ballpoint_pens list and the fountain_pens one.

Does someone have an idea about it ?

Answer 1

In fact, it is very easy to do, I have just inherited my class Pen in two subclasses and changed the GenericRelation parameter, sorry for the disagreement :

class BallPointPen(Pen):
  pass

class FountainPen(Pen):
  pass

class PencilCase(models.Model)
  ballpoint_pens = generic.GenericRelation(BallPointPen, related_name="ballpointpencil+")
  fountain_pens = generic.GenericRelation(FountainPen, related_name="fountainpencil+")

And it works like a charm.