Django: Initializing a FormSet of custom forms with instances

Question

Given the following models:

class Graph(models.Model):     owner = models.ForeignKey(User)      def __unicode__(self):         return u'%d' % self.id  class Point(models.Model):     graph = models.ForeignKey(Graph)      date  = models.DateField(primary_key = True)     abs   = models.FloatField(null = True)     avg   = models.FloatField(null = True)      def __unicode__(self):         return u'%s' % self.date 

I am trying to create a form for editing lists of Points. The HTML input tags require additional attributes to be set, so I am using the following custom form:

class PointForm(forms.ModelForm):     graph = forms.ModelChoiceField(queryset = Graph.objects.all(),                                    widget   = forms.HiddenInput())     date  = forms.DateField(widget = forms.HiddenInput(), label = 'date')     abs   = forms.FloatField(widget = forms.TextInput(                                       attrs = {'class': 'abs-field'}),                             required = False)      class Meta:         model  = Point         fields = ('graph', 'date', 'abs')  # Other fields are not edited.      def pretty_date(self):         return self.data.strftime('%B') 

At this point I do not know how to pass instances of the Point class to a FormSet:

def edit(request):     PointFormSet = forms.formsets.formset_factory(PointForm, extra = 0)     if request.method == 'POST':         return      # Receive 3 points to edit from the database.     graph, res = Graph.objects.get_or_create(id = 1)     one_day    = datetime.timedelta(days = 1)     today      = datetime.date.today()     do_edit    = []     for date in [today - (x * one_day) for x in range(3)]:         point, res = Point.objects.get_or_create(graph = graph, date = date)         do_edit.append(point)      formset = PointFormSet(????) # How is this initialized with the points? 

I found a hack that somewhat works, but it leads to errors later on when trying to process the resulting POST data:

do_edit = [] for date in [today - (x * one_day) for x in range(3)]:     point, res    = Point.objects.get_or_create(graph = graph, date = date)     data          = point.__dict__.copy()     data['graph'] = graph     do_edit.append(data)  formset = PointFormSet(initial = do_edit) 

How is this done correctly?

For the reference, my template looks like this:

<form action="" method="post"> {{ formset.management_form }} <table>     <tbody>     {% for form in formset.forms %}         <tr>             <td>{{ form.graph }} {{ form.date }} {{ form.pretty_date }}:</td>             <td width="100%">{{ form.abs }}</td>         </tr>     {% endfor %}     </tbody> </table> </form> 

Answer 1

The trick is to use a "ModelFormset" instead of just a formset since they allow initialization with a queryset. The docs are here, what you do is provide a form=* when creating the model formset and queryset=* when your instantiating the formset. The form=* arguement is not well documented (had to dig around in the code a little to make sure it is actually there).

def edit(request):     PointFormSet = modelformset_factory(Point, form = PointForm)     qset = Point.objects.all() #or however your getting your Points to modify     formset = PointFormset(queryset = qset)     if request.method == 'POST':         #deal with posting the data         formset = PointFormset(request.POST)         if formset.is_valid():             #if it is not valid then the "errors" will fall through and be returned             formset.save()         return #to your redirect      context_dict = {'formset':formset,                     #other context info                     }      return render_to_response('your_template.html', context_dict) 

So the code walks through easily. If the request is a GET then the instantiated form is returned to the user. If the request is a POST and the form is not .is_valid() then the errors "fall through" and are returned in the same template. If the request is a POST and the data is valid then the formset is saved.

Hope that helps.

-Will