@ -1246,7 +1246,7 @@ class TreeNode(PolymorphicModel):
blank = False,
on_delete = models.SET_NULL, # Vrcholy s null kořenem jsou sirotci bez ročníku
verbose_name="kořen stromu")
first_child = models.ForeignKey('TreeNode',
first_child = models.OneToOneField('TreeNode',
related_name='father_of_first',
null = True,
blank = True,