ManyToManyField using Through and blank=True still required in admin interface

My model (partial code):

class Observation(models.Model):
    date = models.DateField()
    geom = models.PointField()
    values = models.ManyToManyField(Label, through='Value', null=Tr开发者_JS百科ue, blank=True)
    objects = models.GeoManager()


class Value(models.Model):
    observation = models.ForeignKey(Observation)
    label = models.ForeignKey(Label)
    value = models.CharField(max_length=100)
    objects = models.GeoManager()

When I manage an Observation object in the admin interface, it still says at least one value per observation is required.

Am I doing something wrong, is this a bug, or should I write a derived Admin class to solve this?

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I solved this by improving my ERM. The field values in Observation is obsolete, since you get a value_set from the ForeignKey relation in Value.

Still a weird side effect, but since there were no replies I'll consider it something that doesn't occur often.

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This is happened to me too.

How exactly you got it resolved?

Following modification seems to do the trick: But not sure, what effect it's having at DB level.

class Value(models.Model):
    label = models.ForeignKey(Label, blank=True, null=True)