code: def bind(self, *args, **kwargs):
          
          if self.bound:  # Prevent double-binding
              return
          super(DynamicRelationField, self).bind(*args, **kwargs)
          self.bound = True
          parent_model = getattr(self.parent.Meta, 'model', None)
  
          remote = is_field_remote(parent_model, self.source)
  
          try:
              model_field = get_model_field(parent_model, self.source)
          except:
              # model field may not be available for m2o fields with no
              # related_name
              model_field = None
  
          # Infer `required` and `allow_null`
          if 'required' not in self.kwargs and (
                  remote or (
                      model_field and (
                          model_field.has_default() or model_field.null
                      )
                  )
          ):
              self.required = False
          if 'allow_null' not in self.kwargs and getattr(
                  model_field, 'null', False
          ):
              self.allow_null = True
  
          self.model_field = model_field
docs: Bind to the parent serializer.