When working with foreign keys, it's really easy to detect changes in
the field by writing a custom save method. It would look something
like this:
def save(self, force_insert=False, force_update=False):
old_user = None
if Project.objects.filter(id__exact=self.id).count(): #the project
exists
project = Project.objects.get(id=self.id)
old_user = project.assigned_to #assigned_to field is ForeignKey
(User)
super(Project, self).save()
else: #The project does not exist
super(Project, self).save()
project = Project.objects.get(id=self.id)
new_user = self.assigned_to
if old_user != new_user:
#the assigned_to user has changed. do something
However, after some research and personal testing, it appears you
can't do this with ManyToManyField's because the related table is not
updated until after the save method is called. In light of this, I
wrote a view to detect this change in the front end, but I can't seem
to figure out the proper syntax to detect a change in the m2m field.
Any feedback on my code would be appreciated.
def edit_project(request, project_id):
"""
Edit a project (marcomm_lead is the M2M field)
"""
project = get_object_or_404(Project, id=project_id)
if request.method == 'POST':
form = EditProjectForm(request.POST, instance=project)
if form.is_valid():
old_marcomm =
project.marcomm_lead.all().values_list('email',
flat=True).order_by('email') #store the old marcomm_lead emails
new_project = form.save()
if new_project.marcomm_lead.all(): #if project has
marcomm lead(s)
new_marcomm =
new_project.marcomm_lead.all().values_list('email',
flat=True).order_by('email') #store the new marcomm_lead emails
if new_marcomm != old_marcomm: #not sure if
this works
recipients = []
if len(old_marcomm) > 0: #if there were
old marcomm lead(s)
for lead in new_marcomm:
if lead not in
old_marcomm: #never works. please advise! Only
add lead to list if it was not in the old marcomm list
recipients.append(lead) #add the person's email to the list
else: #there were no old marcomm lead(s)
for lead in new_marcomm: #for
each marcomm lead
recipients.append(lead)
#add the person's email to the list
current_site =
Site.objects.get_current()
subject =
render_to_string('projects/email/
marcomm_lead_subject.txt', { 'project': project })
message =
render_to_string('projects/email/
marcomm_lead_body.txt', { 'site': current_site, 'project': project })
send_mail(subject, message,
settings.DEFAULT_FROM_EMAIL,
recipients)
success_url = project.get_absolute_url()
return HttpResponseRedirect(success_url)
else:
form = EditProjectForm(instance=project)
return render_to_response('projects/edit_project.html', { 'project':
project, 'form': form }, context_instance=RequestContext(request))
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