réaffectation des services inactifs impossible

from django.contrib.humanize.templatetags.humanize import naturaltime

from django.contrib.contenttypes.models import ContentType

from django.http import HttpResponseRedirect

from django.core.exceptions import ValidationError

from djgeojson.views import GeoJSONLayerView

from urllib.parse import urlencode

    readonly_fields = ('switch', 'port', 'up',)

### Forms

class ServiceForm(ModelForm):

    def clean_adhesion(self):

        if self.instance.adhesion.pk != self.cleaned_data['adhesion'].pk \

                and not self.instance.is_active():

            raise ValidationError('Il n’est pas possible de ré-affecter à un autre adhérent un service inactif (i.e. sans allocations actives).')

        return self.cleaned_data['adhesion']

### ModelAdmin

class ServiceAdmin(admin.ModelAdmin):

    fields = ('adhesion', 'service_type', 'label', 'notes', 'loan_equipment', 'get_contribution_link', 'is_active',)

    readonly_fields = ('get_contribution_link', 'is_active',)

    raw_id_fields = ('adhesion',)

    form = ServiceForm

    def save_model(self, request, srv, form, change):

        if 'adhesion' in form.changed_data: