Creating a model and related models with Inline formsets

Question

[I have posted this at the Django users | Google Groups also.]

Using the example in the inline formset docs, I am able to edit objects belonging a particular model (using modelforms). I have been trying to follow the same pattern for creating new objects using inline formsets, but have been unable to clear my head enough to bring out a working view for this purpose.

Using the same example as in the above link, how would I go about creating a new instance of an "Author" model together with its related "Book" objects?

Answer 1

First, create a Author model form.

author_form = AuthorModelForm()

then create a dummy author object:

author = Author()

Then create a inline formset using the dummy author like so:

formset = BookFormSet(instance=author)  #since author is empty, this formset will just be empty forms

Send that off to a template. After the data is returned back to the view, you create the Author:

author = AuthorModelForm(request.POST)
created_author = author.save()  # in practice make sure it's valid first

Now hook the inline formset in with the newly created author and then save:

formset = BookFormSet(request.POST, instance=created_author)
formset.save()   #again, make sure it's valid first

---

edit:

To have no checkboxes on new forms, do this is a template:

{% for form in formset.forms %}
    <table>
    {% for field in form %}
        <tr><th>{{field.label_tag}}</th><td>{{field}}{{field.errors}}</td></tr>
    {% endfor %}

    {% if form.pk %} {# empty forms do not have a pk #}
         <tr><th>Delete?</th><td>{{field.DELETE}}</td></tr>
    {% endif %}
    </table>
{% endfor %}

Answer 2

I'd actually like to propose a small adjustment to nbv4's solution:

Assume that you don't create the empty created_author outside of the if-else statement and thus need to nest the formset inside the author_form.is_valid() to avoid runtime errors when the author_form is not valid (and thus no created_author is instantiated).

Instead of:

if request.method == 'POST':
    author_form = AuthorModelForm(request.POST)
    if author_form.is_valid():
        created_author = author_form.save()
        formset = BookFormSet(request.POST, instance=created_author)
        if formset.is_valid():
            formset.save()
            return HttpResponseRedirect(...)
else:
    ...

Do the following:

if request.method == 'POST':
    author_form = AuthorModelForm(request.POST)
    if author_form.is_valid():
        created_author = author_form.save(commit=False)
        formset = BookFormSet(request.POST, instance=created_author)
        if formset.is_valid():
            created_author.save()
            formset.save()
            return HttpResponseRedirect(...)
else:
    ...

This version avoids committing the created_author until the book_formset has had a chance to validate. The use case to correct for is that someone fills out a valid AuthorForm with an invalid BookFormSet and keeps resubmitting, creating multiple Author records with no Books associated with them. This seems to work for my project-tracker app (replace "Author" with "Project" and "Book" with "Role").

Answer 3

models.py (Contact)

class Contact(models.Model)
    first = models.CharField(max_length=30)
    middle = models.CharField('M.I.',max_length=30, blank=True)
    last = models.CharField(max_length=30)
    sort_order = models.PositiveIntegerField(default=99)

models.py (Link)

class Link(models.Model):
    contact = models.ForeignKey(Contact)
    link = models.URLField()
    description = models.CharField(max_length=30)
    access_date = models.DateField(blank=True,null=True)

forms.py

from django.forms import ModelForm
from contacts.models import Contact

class ContactAjaxForm(ModelForm):
    class Meta:
        model=Contact

views.py

def edit(request,object_id=False):
    LinkFormSet = inlineformset_factory(Contact, Link, extra=1)
    if object_id:
        contact=Contact.objects.get(pk=object_id)
    else:
        contact=Contact()
    if request.method == 'POST':
        f=forms.ContactAjaxForm(request.POST, request.FILES, instance=contact)
        fs = LinkFormSet(request.POST,instance=contact)
        if fs.is_valid() and f.is_valid():
            f.save()
            fs.save()
            return HttpResponse('success')
    else:
        f  = forms.ContactAjaxForm(instance=contact)
        fs = LinkFormSet(instance=contact)
    return render_to_response(
        'contacts/edit.html', 
        {'fs': fs, 'f': f, 'contact': contact}
    )

This is not based on the example in the book, it's edited down from some code on my site. I haven't tested it so there might be some bugs but overall it should be solid. Using an empty instance of Contact isn't the suggested method but it saves a bit of logic and it works.

Edit: Added Link Model, switched to normal Foreign Key instead of Generic Foreign Key which is confusing