old_contents: from django.db.models import ForeignKey, TextField, FloatField, ManyToManyField, BooleanField, CASCADE
  
  from yunity.base.hub_models import Hub, HubMixin
  from yunity.base.models import BaseModel, MaxLengthCharField
  
  
  class Item(BaseModel):
      user = ForeignKey('users.User')
      description = TextField()
      latitude = FloatField(blank=True, null=True)
      longitude = FloatField(blank=True, null=True)
  
  
  class Group(BaseModel, HubMixin):
      name = MaxLengthCharField()
      description = TextField(null=True)
  
  
  
  class Store(BaseModel, HubMixin):
      name = MaxLengthCharField(null=True)
  
  
  class Permission(BaseModel):
      name = MaxLengthCharField(null=True)
  
  
  class Team(BaseModel, HubMixin):
      name = MaxLengthCharField(null=True)
      permissions = ManyToManyField(Permission)
      team_hub = ForeignKey(Hub)
new_contents: from django.db.models import ForeignKey, TextField, FloatField, ManyToManyField, BooleanField, CASCADE
  
  from yunity.base.hub_models import Hub, HubMixin
  from yunity.base.models import BaseModel, MaxLengthCharField
  
  
  class Item(BaseModel):
      user = ForeignKey('users.User')
      description = TextField()
      latitude = FloatField(blank=True, null=True)
      longitude = FloatField(blank=True, null=True)
  
  
  class Group(BaseModel, HubMixin):
      name = MaxLengthCharField()
      description = TextField(null=True)
      parent = ForeignKey('base.Group', null=True, on_delete=CASCADE)
  
      is_content_included_in_parent = BooleanField(default=False)
  
  
  class Store(BaseModel, HubMixin):
      name = MaxLengthCharField(null=True)
  
  
  class Permission(BaseModel):
      name = MaxLengthCharField(null=True)
  
  
  class Team(BaseModel, HubMixin):
      name = MaxLengthCharField(null=True)
      permissions = ManyToManyField(Permission)
      team_hub = ForeignKey(Hub)
subject: Implement group hierarchy