Django m2m field doesn't assign to parent object in view - django

Question

THE CONTEXT
I am trying to implement a tagging system for my project. The various plug-in solutions (taggit, tagulous) are each unsuitable in some way.
I would like to allow users to select from existing tags or create new ones in a Select2 tagging field. Existing tags can be added or removed without problem. My difficulty is in the dynamic generation and assignment of new tags.
MY APPROACH
Select2 helpfully renders the manually-entered tags differently in the DOM from those picked from the database via autocomplete. So upon clicking submit, I have javascript collect the new tags and string them together in the value of a hidden input, then delete them from the Select2 field to avoid any validation errors (the form otherwise POSTs the tag names as the ids, which throws a db error).
In the view, I iterate over the desired new tags. For each entry I create the new tag, then add it to the parent object's related set.
THE PROBLEM
While this successfully creates each tag (verified via Admin) it doesn't add it to the related set.
No errors are generated on the (clearly not succeeding) related set add.
The newly-generated tags are correctly instantiated and can be Select2-chosen and sucessfully assigned on a subsequent UpdateView, so I'm certain the problem lies in the view-assignment of the tags to the parent.
The same code executed via the Django shell work flawlessly, so I don't believe its a simple syntax error.
Thus the locus of the problem seems to be in the POST view code adding newly-generated tags to the parent, but I cannot see where the code goes astray.
Thanks for any insights or advice!
models.py:
class Recipe_tag(models.Model):
id = models.UUIDField(primary_key=True,default=uuid.uuid4,null=False)
tag = models.CharField('Tag name',max_length=32,null=False,unique=True)
def __str__(self):
return str(self.tag)
class Recipe_base(models.Model):
id = models.UUIDField(primary_key=True,default=uuid.uuid4,null=False)
name = models.CharField('Recipe name',max_length=128,null=False)
tags = models.ManyToManyField(Recipe_tag,related_name='recipes',null=True,blank=True)
def __str__(self):
return str(self.name)
The post portion of the view:
def post(self, request, *args, **kwargs):
self.object = None
r = Recipe_base.objects.get(id=self.kwargs.get('pk'))
form = RecipeUpdateTagsForm(request.POST,instance=r)
form_valid = form.is_valid()
if form_valid:
if form.has_changed:
f = form.save(commit=False)
clean = form.cleaned_data
f.addedTags = clean['addedTags']
if f.addedTags == 'placeholder':
pass
else:
new_tags = f.addedTags.split(',')
for new_tag in new_tags:
a = Recipe_tag(tag=new_tag)
a.save()
r.tags.add(a)
f.save()
form.save_m2m()
else:
pass
return self.form_valid(form)
else:
return self.form_invalid(form)

Answer 1

Doing further digging, I found a post on another site in which the OP was experiencing the same issues. The trick is to remove the m2m assignment from the "create" or "update" process entirely, because the final save() that occurs in form_valid will discard any changes to the parent's related set.
In my case, the solution was to punt the iteration/assignment of the new tags to form_valid, directly after the final save() occurs there:
def form_valid(self, form, **kwargs):
self.object = form.save()
addedTags = kwargs['addedTags']
r = Recipe_base.objects.get(id=self.kwargs.get('pk'))
if addedTags == 'placeholder':
pass
else:
new_tags = addedTags.split(',')
for new_tag in new_tags:
a = Recipe_tag(tag=new_tag)
a.save()
# print("debug // new tag: %s, %s" % (a.tag, a.id))
r.tags.add(a)
# print("debug // added %s to %s" % (a.tag,r.id))
return HttpResponseRedirect(self.get_success_url())
def get(self, request, *args, **kwargs):
self.object = Recipe_base.objects.get(id=self.kwargs.get('pk'))
recipe_name = self.object.name
recipe_id = self.kwargs.get('pk')
form = RecipeUpdateForm(instance=Recipe_base.objects.get(id=self.kwargs.get('pk')))
return self.render_to_response(self.get_context_data(form=form,recipe_name=recipe_name,recipe_id=recipe_id))
def post(self, request, *args, **kwargs):
self.object = None
r = Recipe_base.objects.get(id=self.kwargs.get('pk'))
form = RecipeUpdateForm(request.POST,instance=r)
form_valid = form.is_valid()
#print("debug // form_valid PASSED")
if form_valid:
if form.has_changed:
#print("debug // Form changed...")
f = form.save(commit=False)
#print("debug // Passes save C=F")
clean = form.cleaned_data
#print('debug // pre-existing tags: ',clean['tags'])
f.addedTags = clean['addedTags']
addedTags = clean['addedTags']
#print('debug // manual tags: ',clean['addedTags'])
f.save()
form.save_m2m()
#print("debug // Form saved")
else:
#print("debug // Form unchanged, skipping...")
pass
#print("debug // Reached successful return")
return self.form_valid(form, addedTags=addedTags,pk=r.id)
else:
#print("debug // Form fails validation")
#print("debug // Reached unsuccessful return")
return self.form_invalid(form)