title: Error When migrating after using 2 foreign keys of same table
body: <p>in my model I have to have 2 foreign keys that are of same model. i tried related name so makemigrations works fine. but when i'm trying to migrate, it throws an error and says</p>
  
  <pre><code>django.db.utils.ProgrammingError: column "service_requested_by_id" cannot be cast automatically to type uuid
  HINT:  You might need to specify "USING service_requested_by_id::uuid".
  </code></pre>
  
  <p>my model</p>
  
  <pre><code>class Schedule(BaseModel):
      project = models.ForeignKey("projects.Project",null=True,blank=True)
      description = models.TextField(blank=True,null=True)
      vehicle = models.ForeignKey("logistics.Vehicle",null=True,blank=True)
      driver = models.ForeignKey("staffs.Staff",related_name='driver',blank=True,null=True)
      service_requested_by = models.ForeignKey("staffs.Staff",related_name='service_requested_by',blank=True,null=True)
      start_time = models.DateTimeField(null=True,blank=True)
      end_time = models.DateTimeField(null=True,blank=True)
      is_deleted = models.BooleanField(default=False)
      starting_km = models.DecimalField(null=True,blank=True,default=0,decimal_places=0, max_digits=15,validators=[MinValueValidator(Decimal('0'))])
      completed_km = models.DecimalField(null=True,blank=True,default=0,decimal_places=0, max_digits=15,validators=[MinValueValidator(Decimal('0'))])
      travelled_km = models.DecimalField(null=True,blank=True,default=0,decimal_places=0, max_digits=15)
  
      class Meta:
          db_table = 'schedule'
          verbose_name = _('schedule')
          verbose_name_plural = _('schedules')
          ordering = ('vehicle',)  
  
      class Admin:
          list_display = ('vehicle',)
  
      def __unicode__(self):
          if self.vehicle:
              return self.vehicle.name
          else:
             return str(self.project)
  </code></pre>
  
  <p>It was working all fine till i added the service_requested_by field. any hint what i am possibly doing wrong? do i need to post anything else beside this code?</p>