code: def add_columns(self, model, **fields):
          
          for name, field in fields.items():
              model._meta.add_field(name, field)
              self.ops.append(self.migrator.add_column(
                  model._meta.table_name, field.column_name, field))
              if field.unique:
                  self.ops.append(self.migrator.add_index(
                      model._meta.table_name, (field.column_name,), unique=True))
          return model
docs: Create new fields.