mpen mpen - 4 months ago 10
Python Question

Django edit form based on add form?

I've made a nice form, and a big complicated 'add' function for handling it. It starts like this...

def add(req):
if req.method == 'POST':
form = ArticleForm(req.POST)
if form.is_valid():
article = form.save(commit=False)
article.author = req.user
# more processing ...


Now I don't really want to duplicate all that functionality in the
edit()
method, so I figured
edit
could use the exact same template, and maybe just add an
id
field to the form so the
add
function knew what it was editing. But there's a couple problems with this


  1. Where would I set
    article.id
    in the
    add
    func? It would have to be after
    form.save
    because that's where the article gets created, but it would never even reach that, because the form is invalid due to unique constraints (unless the user edited everything). I can just remove the
    is_valid
    check, but then
    form.save
    fails instead.

  2. If the form actually is invalid, the field I dynamically added in the edit function isn't preserved.



So how do I deal with this?

Answer

If you are extending your form from a ModelForm, use the instance keyword argument. Here we pass either an existing instance or a new one, depending on whether we're editing or adding an existing article. In both cases the author field is set on the instance, so commit=False is not required. Note also that I'm assuming only the author may edit their own articles, hence the HttpResponseForbidden response.

from django.http import HttpResponseForbidden
from django.shortcuts import get_object_or_404, redirect, render, reverse


@login_required
def edit(request, id=None, template_name='article_edit_template.html'):
    if id:
        article = get_object_or_404(Article, pk=id)
        if article.author != request.user:
            return HttpResponseForbidden()
    else:
        article = Article(author=request.user)

    form = ArticleForm(request.POST or None, instance=article)
    if request.POST and form.is_valid():
        form.save()

        # Save was successful, so redirect to another page
        redirect_url = reverse(article_save_success)
        return redirect(redirect_url)

    return render(request, template_name, {
        'form': form
    })

And in your urls.py:

(r'^article/new/$', views.edit, {}, 'article_new'),
(r'^article/edit/(?P<id>\d+)/$', views.edit, {}, 'article_edit'),

The same edit view is used for both adds and edits, but only the edit url pattern passes an id to the view. To make this work well with your form you'll need to omit the author field from the form:

class ArticleForm(forms.ModelForm):
    class Meta:
        model = Article
        exclude = ('author',)