A formset is a layer of abstraction to working with multiple forms on the same page. It can be best compared to a data grid. Let’s say you have the following form:
>>> from django import forms
>>> class ArticleForm(forms.Form):
... title = forms.CharField()
... pub_date = forms.DateField()
You might want to allow the user to create several articles at once. To create a formset out of an ArticleForm you would do:
>>> from django.forms.formsets import formset_factory
>>> ArticleFormSet = formset_factory(ArticleForm)
You now have created a formset named ArticleFormSet. The formset gives you the ability to iterate over the forms in the formset and display them as you would with a regular form:
>>> formset = ArticleFormSet()
>>> for form in formset.forms:
... print form.as_table()
<tr><th><label for="id_form-0-title">Title:</label></th><td><input type="text" name="form-0-title" id="id_form-0-title" /></td></tr>
<tr><th><label for="id_form-0-pub_date">Pub date:</label></th><td><input type="text" name="form-0-pub_date" id="id_form-0-pub_date" /></td></tr>
As you can see it only displayed one form. This is because by default the formset_factory defines one extra form. This can be controlled with the extra parameter:
>>> ArticleFormSet = formset_factory(ArticleForm, extra=2)
Initial data is what drives the main usability of a formset. As shown above you can define the number of extra forms. What this means is that you are telling the formset how many additional forms to show in addition to the number of forms it generates from the initial data. Lets take a look at an example:
>>> ArticleFormSet = formset_factory(ArticleForm, extra=2)
>>> formset = ArticleFormSet(initial=[
... {'title': u'Django is now open source',
... 'pub_date': datetime.date.today()},
... ])
>>> for form in formset.forms:
... print form.as_table()
<tr><th><label for="id_form-0-title">Title:</label></th><td><input type="text" name="form-0-title" value="Django is now open source" id="id_form-0-title" /></td></tr>
<tr><th><label for="id_form-0-pub_date">Pub date:</label></th><td><input type="text" name="form-0-pub_date" value="2008-05-12" id="id_form-0-pub_date" /></td></tr>
<tr><th><label for="id_form-1-title">Title:</label></th><td><input type="text" name="form-1-title" id="id_form-1-title" /></td></tr>
<tr><th><label for="id_form-1-pub_date">Pub date:</label></th><td><input type="text" name="form-1-pub_date" id="id_form-1-pub_date" /></td></tr>
<tr><th><label for="id_form-2-title">Title:</label></th><td><input type="text" name="form-2-title" id="id_form-2-title" /></td></tr>
<tr><th><label for="id_form-2-pub_date">Pub date:</label></th><td><input type="text" name="form-2-pub_date" id="id_form-2-pub_date" /></td></tr>
There are now a total of three forms showing above. One for the initial data that was passed in and two extra forms. Also note that we are passing in a list of dictionaries as the initial data.
The max_num parameter to formset_factory gives you the ability to force the maximum number of forms the formset will display:
>>> ArticleFormSet = formset_factory(ArticleForm, extra=2, max_num=1)
>>> formset = ArticleFormset()
>>> for form in formset.forms:
... print form.as_table()
<tr><th><label for="id_form-0-title">Title:</label></th><td><input type="text" name="form-0-title" id="id_form-0-title" /></td></tr>
<tr><th><label for="id_form-0-pub_date">Pub date:</label></th><td><input type="text" name="form-0-pub_date" id="id_form-0-pub_date" /></td></tr>
A max_num value of 0 (the default) puts no limit on the number forms displayed.
Validation with a formset is almost identical to a regular Form. There is an is_valid method on the formset to provide a convenient way to validate all forms in the formset:
>>> ArticleFormSet = formset_factory(ArticleForm)
>>> formset = ArticleFormSet({})
>>> formset.is_valid()
True
We passed in no data to the formset which is resulting in a valid form. The formset is smart enough to ignore extra forms that were not changed. If we provide an invalid article:
>>> data = {
... 'form-TOTAL_FORMS': u'2',
... 'form-INITIAL_FORMS': u'0',
... 'form-0-title': u'Test',
... 'form-0-pub_date': u'16 June 1904',
... 'form-1-title': u'Test',
... 'form-1-pub_date': u'', # <-- this date is missing but required
... }
>>> formset = ArticleFormSet(data)
>>> formset.is_valid()
False
>>> formset.errors
[{}, {'pub_date': [u'This field is required.']}]
As we can see, formset.errors is a list whose entries correspond to the forms in the formset. Validation was performed for each of the two forms, and the expected error message appears for the second item.
You may have noticed the additional data that was required in the formset's data above. This data is coming from the ManagementForm. This form is dealt with internally to the formset. If you don't use it, it will result in an exception:
>>> data = {
... 'form-0-title': u'Test',
... 'form-0-pub_date': u'',
... }
>>> formset = ArticleFormSet(data)
...
django.forms.util.ValidationError: [u'ManagementForm data is missing or has been tampered with']
It is used to keep track of how many form instances are being displayed. If you are adding new forms via JavaScript, you should increment the count fields in this form as well.
BaseModelFormSet has a couple of methods that are closely related to the ManagementForm, total_form_count and initial_form_count.
total_form_count returns the total number of forms in this formset. initial_form_count returns the number of forms in the formset that were pre-filled, and is also used to determine how many forms are required. You will probably never need to override either of these methods, so please be sure you understand what they do before doing so.
A formset has a clean method similar to the one on a Form class. This is where you define your own validation that works at the formset level:
>>> from django.forms.formsets import BaseFormSet
>>> class BaseArticleFormSet(BaseFormSet):
... def clean(self):
... """Checks that no two articles have the same title."""
... if any(self.errors):
... # Don't bother validating the formset unless each form is valid on its own
... return
... titles = []
... for i in range(0, self.total_form_count()):
... form = self.forms[i]
... title = form.cleaned_data['title']
... if title in titles:
... raise forms.ValidationError, "Articles in a set must have distinct titles."
... titles.append(title)
>>> ArticleFormSet = formset_factory(ArticleForm, formset=BaseArticleFormSet)
>>> data = {
... 'form-TOTAL_FORMS': u'2',
... 'form-INITIAL_FORMS': u'0',
... 'form-0-title': u'Test',
... 'form-0-pub_date': u'16 June 1904',
... 'form-1-title': u'Test',
... 'form-1-pub_date': u'23 June 1912',
... }
>>> formset = ArticleFormSet(data)
>>> formset.is_valid()
False
>>> formset.errors
[{}, {}]
>>> formset.non_form_errors()
[u'Articles in a set must have distinct titles.']
The formset clean method is called after all the Form.clean methods have been called. The errors will be found using the non_form_errors() method on the formset.
Common use cases with a formset is dealing with ordering and deletion of the form instances. This has been dealt with for you. The formset_factory provides two optional parameters can_order and can_delete that will do the extra work of adding the extra fields and providing simpler ways of getting to that data.
Default: False
Lets create a formset with the ability to order:
>>> ArticleFormSet = formset_factory(ArticleForm, can_order=True)
>>> formset = ArticleFormSet(initial=[
... {'title': u'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': u'Article #2', 'pub_date': datetime.date(2008, 5, 11)},
... ])
>>> for form in formset.forms:
... print form.as_table()
<tr><th><label for="id_form-0-title">Title:</label></th><td><input type="text" name="form-0-title" value="Article #1" id="id_form-0-title" /></td></tr>
<tr><th><label for="id_form-0-pub_date">Pub date:</label></th><td><input type="text" name="form-0-pub_date" value="2008-05-10" id="id_form-0-pub_date" /></td></tr>
<tr><th><label for="id_form-0-ORDER">Order:</label></th><td><input type="text" name="form-0-ORDER" value="1" id="id_form-0-ORDER" /></td></tr>
<tr><th><label for="id_form-1-title">Title:</label></th><td><input type="text" name="form-1-title" value="Article #2" id="id_form-1-title" /></td></tr>
<tr><th><label for="id_form-1-pub_date">Pub date:</label></th><td><input type="text" name="form-1-pub_date" value="2008-05-11" id="id_form-1-pub_date" /></td></tr>
<tr><th><label for="id_form-1-ORDER">Order:</label></th><td><input type="text" name="form-1-ORDER" value="2" id="id_form-1-ORDER" /></td></tr>
<tr><th><label for="id_form-2-title">Title:</label></th><td><input type="text" name="form-2-title" id="id_form-2-title" /></td></tr>
<tr><th><label for="id_form-2-pub_date">Pub date:</label></th><td><input type="text" name="form-2-pub_date" id="id_form-2-pub_date" /></td></tr>
<tr><th><label for="id_form-2-ORDER">Order:</label></th><td><input type="text" name="form-2-ORDER" id="id_form-2-ORDER" /></td></tr>
This adds an additional field to each form. This new field is named ORDER and is an forms.IntegerField. For the forms that came from the initial data it automatically assigned them a numeric value. Lets look at what will happen when the user changes these values:
>>> data = {
... 'form-TOTAL_FORMS': u'3',
... 'form-INITIAL_FORMS': u'2',
... 'form-0-title': u'Article #1',
... 'form-0-pub_date': u'2008-05-10',
... 'form-0-ORDER': u'2',
... 'form-1-title': u'Article #2',
... 'form-1-pub_date': u'2008-05-11',
... 'form-1-ORDER': u'1',
... 'form-2-title': u'Article #3',
... 'form-2-pub_date': u'2008-05-01',
... 'form-2-ORDER': u'0',
... }
>>> formset = ArticleFormSet(data, initial=[
... {'title': u'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': u'Article #2', 'pub_date': datetime.date(2008, 5, 11)},
... ])
>>> formset.is_valid()
True
>>> for form in formset.ordered_forms:
... print form.cleaned_data
{'pub_date': datetime.date(2008, 5, 1), 'ORDER': 0, 'title': u'Article #3'}
{'pub_date': datetime.date(2008, 5, 11), 'ORDER': 1, 'title': u'Article #2'}
{'pub_date': datetime.date(2008, 5, 10), 'ORDER': 2, 'title': u'Article #1'}
Default: False
Lets create a formset with the ability to delete:
>>> ArticleFormSet = formset_factory(ArticleForm, can_delete=True)
>>> formset = ArticleFormSet(initial=[
... {'title': u'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': u'Article #2', 'pub_date': datetime.date(2008, 5, 11)},
... ])
>>> for form in formset.forms:
.... print form.as_table()
<input type="hidden" name="form-TOTAL_FORMS" value="3" id="id_form-TOTAL_FORMS" /><input type="hidden" name="form-INITIAL_FORMS" value="2" id="id_form-INITIAL_FORMS" />
<tr><th><label for="id_form-0-title">Title:</label></th><td><input type="text" name="form-0-title" value="Article #1" id="id_form-0-title" /></td></tr>
<tr><th><label for="id_form-0-pub_date">Pub date:</label></th><td><input type="text" name="form-0-pub_date" value="2008-05-10" id="id_form-0-pub_date" /></td></tr>
<tr><th><label for="id_form-0-DELETE">Delete:</label></th><td><input type="checkbox" name="form-0-DELETE" id="id_form-0-DELETE" /></td></tr>
<tr><th><label for="id_form-1-title">Title:</label></th><td><input type="text" name="form-1-title" value="Article #2" id="id_form-1-title" /></td></tr>
<tr><th><label for="id_form-1-pub_date">Pub date:</label></th><td><input type="text" name="form-1-pub_date" value="2008-05-11" id="id_form-1-pub_date" /></td></tr>
<tr><th><label for="id_form-1-DELETE">Delete:</label></th><td><input type="checkbox" name="form-1-DELETE" id="id_form-1-DELETE" /></td></tr>
<tr><th><label for="id_form-2-title">Title:</label></th><td><input type="text" name="form-2-title" id="id_form-2-title" /></td></tr>
<tr><th><label for="id_form-2-pub_date">Pub date:</label></th><td><input type="text" name="form-2-pub_date" id="id_form-2-pub_date" /></td></tr>
<tr><th><label for="id_form-2-DELETE">Delete:</label></th><td><input type="checkbox" name="form-2-DELETE" id="id_form-2-DELETE" /></td></tr>
Similar to can_order this adds a new field to each form named DELETE and is a forms.BooleanField. When data comes through marking any of the delete fields you can access them with deleted_forms:
>>> data = {
... 'form-TOTAL_FORMS': u'3',
... 'form-INITIAL_FORMS': u'2',
... 'form-0-title': u'Article #1',
... 'form-0-pub_date': u'2008-05-10',
... 'form-0-DELETE': u'on',
... 'form-1-title': u'Article #2',
... 'form-1-pub_date': u'2008-05-11',
... 'form-1-DELETE': u'',
... 'form-2-title': u'',
... 'form-2-pub_date': u'',
... 'form-2-DELETE': u'',
... }
>>> formset = ArticleFormSet(data, initial=[
... {'title': u'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': u'Article #2', 'pub_date': datetime.date(2008, 5, 11)},
... ])
>>> [form.cleaned_data for form in formset.deleted_forms]
[{'DELETE': True, 'pub_date': datetime.date(2008, 5, 10), 'title': u'Article #1'}]
If you need to add additional fields to the formset this can be easily accomplished. The formset base class provides an add_fields method. You can simply override this method to add your own fields or even redefine the default fields/attributes of the order and deletion fields:
>>> class BaseArticleFormSet(BaseFormSet):
... def add_fields(self, form, index):
... super(BaseArticleFormSet, self).add_fields(form, index)
... form.fields["my_field"] = forms.CharField()
>>> ArticleFormSet = formset_factory(ArticleForm, formset=BaseArticleFormSet)
>>> formset = ArticleFormSet()
>>> for form in formset.forms:
... print form.as_table()
<tr><th><label for="id_form-0-title">Title:</label></th><td><input type="text" name="form-0-title" id="id_form-0-title" /></td></tr>
<tr><th><label for="id_form-0-pub_date">Pub date:</label></th><td><input type="text" name="form-0-pub_date" id="id_form-0-pub_date" /></td></tr>
<tr><th><label for="id_form-0-my_field">My field:</label></th><td><input type="text" name="form-0-my_field" id="id_form-0-my_field" /></td></tr>
Using a formset inside a view is as easy as using a regular Form class. The only thing you will want to be aware of is making sure to use the management form inside the template. Let's look at a sample view:
def manage_articles(request):
ArticleFormSet = formset_factory(ArticleForm)
if request.method == 'POST':
formset = ArticleFormSet(request.POST, request.FILES)
if formset.is_valid():
# do something with the formset.cleaned_data
else:
formset = ArticleFormSet()
return render_to_response('manage_articles.html', {'formset': formset})
The manage_articles.html template might look like this:
<form method="POST" action="">
{{ formset.management_form }}
<table>
{% for form in formset.forms %}
{{ form }}
{% endfor %}
</table>
</form>
However the above can be slightly shortcutted and let the formset itself deal with the management form:
<form method="POST" action="">
<table>
{{ formset }}
</table>
</form>
The above ends up calling the as_table method on the formset class.
You are able to use more than one formset in a view if you like. Formsets borrow much of its behavior from forms. With that said you are able to use prefix to prefix formset form field names with a given value to allow more than one formset to be sent to a view without name clashing. Lets take a look at how this might be accomplished:
def manage_articles(request):
ArticleFormSet = formset_factory(ArticleForm)
BookFormSet = formset_factory(BookForm)
if request.method == 'POST':
article_formset = ArticleFormSet(request.POST, request.FILES, prefix='articles')
book_formset = BookFormSet(request.POST, request.FILES, prefix='books')
if article_formset.is_valid() and book_formset.is_valid():
# do something with the cleaned_data on the formsets.
else:
article_formset = ArticleFormSet(prefix='articles')
book_formset = BookFormSet(prefix='books')
return render_to_response('manage_articles.html', {
'article_formset': article_formset,
'book_formset': book_formset,
})
You would then render the formsets as normal. It is important to point out that you need to pass prefix on both the POST and non-POST cases so that it is rendered and processed correctly.
Sep 20, 2009