Forbid adding a loan when there is already one running

# -*- coding: utf-8 -*-

from __future__ import unicode_literals

from django.core.exceptions import ValidationError

from django.db import models

from django.db.models import Q

from django.conf import settings

    is_running.boolean = True

    is_running.short_description = 'En cours ?'

    def clean(self):

        current_loan = self.item.get_current_loan()

        if (

                self.is_running()

                and

                current_loan

                and

                self.item.get_current_loan() != self

        ):

            raise ValidationError(

                "Il y a déjà un emprunt en cours sur cet objet")

    class Meta:

        verbose_name = 'prêt d’objet'

        verbose_name_plural = 'prêts d’objets'