Django: using ModelForm to edit existing database entry

Question

I have created a ModelForm class to be able to create and edit database entries. Creating new entries works well, however, i dont know how to use ModelForms to edit/update an existing entry. I can instantiate a ModelForm with a database instance using:

form  = MyModelForm(instance=MyModel.objects.get(pk=some_id))

However, when i pass this to a template and edit a field and then try to save it, i create a new database entry instead of updating "some_id"?

Edit1: This is my view

def editData(request):
if request.method == 'POST':
    form = MyModelForm(request.POST, request.FILES)

    if form.is_valid():
        editedEntry = form.save() # <-- creates new entry, instead of updating

Daniel Roseman · Accepted Answer · 2011-09-08 15:21:33Z

59

Remember you still need to use the instance parameter when you instantiate on POST.

instance = MyModel.objects.get(whatever)
if request.method == "POST":
    form = MyModelForm(request.POST, instance=instance)
    ...

else:
    form = MyModelForm(instance=instance)

answered Sep 8, 2011 at 15:21

Daniel Roseman

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4 Comments

WesDec Over a year ago

Ok i was not doing that. So how should i pass my primary key "some_id" to the html template and back again to the view. Should i do it manually as a hidden form field or is there a way to have Django take care of it?

Daniel Roseman Over a year ago

There's no need to do that. Just use the pattern as I show above.

WesDec Over a year ago

But to do this: instance = MyModel.objects.get(whatever), i need to substitute "whatever" with the primary key "some_id" which i used to create the initial MyModelForm. From where do i get that?

Daniel Roseman Over a year ago

From the same place you got it from originally, ie the URL.

Davy · Accepted Answer · 2016-11-04 19:47:23Z

3

Also possible and slightly shorter:

instance = MyModel.objects.get(whatever)
form = MyModelForm(request.POST or None, instance=instance)
...

answered Nov 4, 2016 at 19:47

Davy

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