new_contents: from django.db import models
  
  
  class Membership(models.Model):
      date_joined = models.DateField(auto_now_add=True)
      gestalt = models.ForeignKey('entities.Gestalt')
      group = models.ForeignKey('entities.Group')
  
      class Meta:
          unique_together = ('gestalt', 'group')
  
subject: Add new membership model