A formset is a layer of abstraction to work 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 import formset_factory
>>> ArticleFormSet = formset_factory(ArticleForm)
You now have created a formset class named ArticleFormSet.
Instantiating 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:
... 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 empty form. The number of empty forms
that is displayed is controlled by the extra parameter. By default,
formset_factory() defines one extra form; the
following example will create a formset class to display two blank forms:
>>> ArticleFormSet = formset_factory(ArticleForm, extra=2)
Iterating over a formset will render the forms in the order they were
created. You can change this order by providing an alternate implementation for
the __iter__() method.
Formsets can also be indexed into, which returns the corresponding form. If you
override __iter__, you will need to also override __getitem__ to have
matching behavior.
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. Let’s take a look at an example:
>>> import datetime
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> ArticleFormSet = formset_factory(ArticleForm, extra=2)
>>> formset = ArticleFormSet(initial=[
... {'title': 'Django is now open source',
... 'pub_date': datetime.date.today(),}
... ])
>>> for form in formset:
... 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.
If you use an initial for displaying a formset, you should pass the same
initial when processing that formset’s submission so that the formset can
detect which forms were changed by the user. For example, you might have
something like: ArticleFormSet(request.POST, initial=[...]).
The max_num parameter to formset_factory()
gives you the ability to limit the number of forms the formset will display:
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> ArticleFormSet = formset_factory(ArticleForm, extra=2, max_num=1)
>>> formset = ArticleFormSet()
>>> for form in formset:
... 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>
If the value of max_num is greater than the number of existing items in the
initial data, up to extra additional blank forms will be added to the
formset, so long as the total number of forms does not exceed max_num. For
example, if extra=2 and max_num=2 and the formset is initialized with
one initial item, a form for the initial item and one blank form will be
displayed.
If the number of items in the initial data exceeds max_num, all initial
data forms will be displayed regardless of the value of max_num and no
extra forms will be displayed. For example, if extra=3 and max_num=1
and the formset is initialized with two initial items, two forms with the
initial data will be displayed.
A max_num value of None (the default) puts a high limit on the number
of forms displayed (1000). In practice this is equivalent to no limit.
By default, max_num only affects how many forms are displayed and does not
affect validation. If validate_max=True is passed to the
formset_factory(), then max_num will affect
validation. See validate_max.
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:
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> ArticleFormSet = formset_factory(ArticleForm)
>>> data = {
... 'form-TOTAL_FORMS': '1',
... 'form-INITIAL_FORMS': '0',
... 'form-MAX_NUM_FORMS': '',
... }
>>> formset = ArticleFormSet(data)
>>> 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': '2',
... 'form-INITIAL_FORMS': '0',
... 'form-MAX_NUM_FORMS': '',
... 'form-0-title': 'Test',
... 'form-0-pub_date': '1904-06-16',
... 'form-1-title': 'Test',
... 'form-1-pub_date': '', # <-- this date is missing but required
... }
>>> formset = ArticleFormSet(data)
>>> formset.is_valid()
False
>>> formset.errors
[{}, {'pub_date': ['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.
Just like when using a normal Form, each field in a formset’s forms may
include HTML attributes such as maxlength for browser validation. However,
form fields of formsets won’t include the required attribute as that
validation may be incorrect when adding and deleting forms.
To check how many errors there are in the formset, we can use the
total_error_count method:
>>> # Using the previous example
>>> formset.errors
[{}, {'pub_date': ['This field is required.']}]
>>> len(formset.errors)
2
>>> formset.total_error_count()
1
We can also check if form data differs from the initial data (i.e. the form was sent without any data):
>>> data = {
... 'form-TOTAL_FORMS': '1',
... 'form-INITIAL_FORMS': '0',
... 'form-MAX_NUM_FORMS': '',
... 'form-0-title': '',
... 'form-0-pub_date': '',
... }
>>> formset = ArticleFormSet(data)
>>> formset.has_changed()
False
ManagementForm¶You may have noticed the additional data (form-TOTAL_FORMS,
form-INITIAL_FORMS and form-MAX_NUM_FORMS) that was required
in the formset’s data above. This data is required for the
ManagementForm. This form is used by the formset to manage the
collection of forms contained in the formset. If you don’t provide
this management data, an exception will be raised:
>>> data = {
... 'form-0-title': 'Test',
... 'form-0-pub_date': '',
... }
>>> formset = ArticleFormSet(data)
>>> formset.is_valid()
Traceback (most recent call last):
...
django.forms.utils.ValidationError: ['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. On the other hand, if you are using JavaScript to allow
deletion of existing objects, then you need to ensure the ones being removed
are properly marked for deletion by including form-#-DELETE in the POST
data. It is expected that all forms are present in the POST data regardless.
The management form is available as an attribute of the formset
itself. When rendering a formset in a template, you can include all
the management data by rendering {{ my_formset.management_form }}
(substituting the name of your formset as appropriate).
total_form_count and initial_form_count¶BaseFormSet 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.
empty_form¶BaseFormSet provides an additional attribute empty_form which returns
a form instance with a prefix of __prefix__ for easier use in dynamic
forms with JavaScript.
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 import BaseFormSet
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> 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 form in self.forms:
... if self.can_delete and self._should_delete_form(form):
... continue
... title = form.cleaned_data.get('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': '2',
... 'form-INITIAL_FORMS': '0',
... 'form-MAX_NUM_FORMS': '',
... 'form-0-title': 'Test',
... 'form-0-pub_date': '1904-06-16',
... 'form-1-title': 'Test',
... 'form-1-pub_date': '1912-06-23',
... }
>>> formset = ArticleFormSet(data)
>>> formset.is_valid()
False
>>> formset.errors
[{}, {}]
>>> formset.non_form_errors()
['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.
Django provides a couple ways to validate the minimum or maximum number of submitted forms. Applications which need more customizable validation of the number of forms should use custom formset validation.
validate_max¶If validate_max=True is passed to
formset_factory(), validation will also check
that the number of forms in the data set, minus those marked for
deletion, is less than or equal to max_num.
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> ArticleFormSet = formset_factory(ArticleForm, max_num=1, validate_max=True)
>>> data = {
... 'form-TOTAL_FORMS': '2',
... 'form-INITIAL_FORMS': '0',
... 'form-MIN_NUM_FORMS': '',
... 'form-MAX_NUM_FORMS': '',
... 'form-0-title': 'Test',
... 'form-0-pub_date': '1904-06-16',
... 'form-1-title': 'Test 2',
... 'form-1-pub_date': '1912-06-23',
... }
>>> formset = ArticleFormSet(data)
>>> formset.is_valid()
False
>>> formset.errors
[{}, {}]
>>> formset.non_form_errors()
['Please submit 1 or fewer forms.']
validate_max=True validates against max_num strictly even if
max_num was exceeded because the amount of initial data supplied was
excessive.
Note
Regardless of validate_max, if the number of forms in a data set
exceeds max_num by more than 1000, then the form will fail to validate
as if validate_max were set, and additionally only the first 1000
forms above max_num will be validated. The remainder will be
truncated entirely. This is to protect against memory exhaustion attacks
using forged POST requests.
validate_min¶If validate_min=True is passed to
formset_factory(), validation will also check
that the number of forms in the data set, minus those marked for
deletion, is greater than or equal to min_num.
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> ArticleFormSet = formset_factory(ArticleForm, min_num=3, validate_min=True)
>>> data = {
... 'form-TOTAL_FORMS': '2',
... 'form-INITIAL_FORMS': '0',
... 'form-MIN_NUM_FORMS': '',
... 'form-MAX_NUM_FORMS': '',
... 'form-0-title': 'Test',
... 'form-0-pub_date': '1904-06-16',
... 'form-1-title': 'Test 2',
... 'form-1-pub_date': '1912-06-23',
... }
>>> formset = ArticleFormSet(data)
>>> formset.is_valid()
False
>>> formset.errors
[{}, {}]
>>> formset.non_form_errors()
['Please submit 3 or more forms.']
The formset_factory() provides two optional
parameters can_order and can_delete to help with ordering of forms in
formsets and deletion of forms from a formset.
can_order¶BaseFormSet.can_order¶Default: False
Lets you create a formset with the ability to order:
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> ArticleFormSet = formset_factory(ArticleForm, can_order=True)
>>> formset = ArticleFormSet(initial=[
... {'title': 'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': 'Article #2', 'pub_date': datetime.date(2008, 5, 11)},
... ])
>>> for form in formset:
... 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="number" 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="number" 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="number" 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. Let’s look at what will
happen when the user changes these values:
>>> data = {
... 'form-TOTAL_FORMS': '3',
... 'form-INITIAL_FORMS': '2',
... 'form-MAX_NUM_FORMS': '',
... 'form-0-title': 'Article #1',
... 'form-0-pub_date': '2008-05-10',
... 'form-0-ORDER': '2',
... 'form-1-title': 'Article #2',
... 'form-1-pub_date': '2008-05-11',
... 'form-1-ORDER': '1',
... 'form-2-title': 'Article #3',
... 'form-2-pub_date': '2008-05-01',
... 'form-2-ORDER': '0',
... }
>>> formset = ArticleFormSet(data, initial=[
... {'title': 'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': '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': 'Article #3'}
{'pub_date': datetime.date(2008, 5, 11), 'ORDER': 1, 'title': 'Article #2'}
{'pub_date': datetime.date(2008, 5, 10), 'ORDER': 2, 'title': 'Article #1'}
can_delete¶BaseFormSet.can_delete¶Default: False
Lets you create a formset with the ability to select forms for deletion:
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> ArticleFormSet = formset_factory(ArticleForm, can_delete=True)
>>> formset = ArticleFormSet(initial=[
... {'title': 'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': 'Article #2', 'pub_date': datetime.date(2008, 5, 11)},
... ])
>>> for form in formset:
... 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-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': '3',
... 'form-INITIAL_FORMS': '2',
... 'form-MAX_NUM_FORMS': '',
... 'form-0-title': 'Article #1',
... 'form-0-pub_date': '2008-05-10',
... 'form-0-DELETE': 'on',
... 'form-1-title': 'Article #2',
... 'form-1-pub_date': '2008-05-11',
... 'form-1-DELETE': '',
... 'form-2-title': '',
... 'form-2-pub_date': '',
... 'form-2-DELETE': '',
... }
>>> formset = ArticleFormSet(data, initial=[
... {'title': 'Article #1', 'pub_date': datetime.date(2008, 5, 10)},
... {'title': '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': 'Article #1'}]
If you are using a ModelFormSet,
model instances for deleted forms will be deleted when you call
formset.save().
If you call formset.save(commit=False), objects will not be deleted
automatically. You’ll need to call delete() on each of the
formset.deleted_objects to actually delete
them:
>>> instances = formset.save(commit=False)
>>> for obj in formset.deleted_objects:
... obj.delete()
On the other hand, if you are using a plain FormSet, it’s up to you to
handle formset.deleted_forms, perhaps in your formset’s save() method,
as there’s no general notion of what it means to delete a form.
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:
>>> from django.forms import BaseFormSet
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> class BaseArticleFormSet(BaseFormSet):
... def add_fields(self, form, index):
... super().add_fields(form, index)
... form.fields["my_field"] = forms.CharField()
>>> ArticleFormSet = formset_factory(ArticleForm, formset=BaseArticleFormSet)
>>> formset = ArticleFormSet()
>>> for form in formset:
... 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>
Sometimes your form class takes custom parameters, like MyArticleForm.
You can pass this parameter when instantiating the formset:
>>> from django.forms import BaseFormSet
>>> from django.forms import formset_factory
>>> from myapp.forms import ArticleForm
>>> class MyArticleForm(ArticleForm):
... def __init__(self, *args, user, **kwargs):
... self.user = user
... super().__init__(*args, **kwargs)
>>> ArticleFormSet = formset_factory(MyArticleForm)
>>> formset = ArticleFormSet(form_kwargs={'user': request.user})
The form_kwargs may also depend on the specific form instance. The formset
base class provides a get_form_kwargs method. The method takes a single
argument - the index of the form in the formset. The index is None for the
empty_form:
>>> from django.forms import BaseFormSet
>>> from django.forms import formset_factory
>>> class BaseArticleFormSet(BaseFormSet):
... def get_form_kwargs(self, index):
... kwargs = super().get_form_kwargs(index)
... kwargs['custom_kwarg'] = index
... return kwargs
In the rendered HTML, formsets include a prefix on each field’s name. By
default, the prefix is 'form', but it can be customized using the formset’s
prefix argument.
For example, in the default case, you might see:
<label for="id_form-0-title">Title:</label>
<input type="text" name="form-0-title" id="id_form-0-title">
But with ArticleFormset(prefix='article') that becomes:
<label for="id_article-0-title">Title:</label>
<input type="text" name="article-0-title" id="id_article-0-title">
This is useful if you want to use more than one formset in a view.
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:
from django.forms import formset_factory
from django.shortcuts import render
from myapp.forms import ArticleForm
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
pass
else:
formset = ArticleFormSet()
return render(request, 'manage_articles.html', {'formset': formset})
The manage_articles.html template might look like this:
<form method="post">
{{ formset.management_form }}
<table>
{% for form in formset %}
{{ form }}
{% endfor %}
</table>
</form>
However there’s a slight shortcut for the above by letting the formset itself deal with the management form:
<form method="post">
<table>
{{ formset }}
</table>
</form>
The above ends up calling the as_table method on the formset class.
can_delete and can_order¶If you manually render fields in the template, you can render
can_delete parameter with {{ form.DELETE }}:
<form method="post">
{{ formset.management_form }}
{% for form in formset %}
<ul>
<li>{{ form.title }}</li>
<li>{{ form.pub_date }}</li>
{% if formset.can_delete %}
<li>{{ form.DELETE }}</li>
{% endif %}
</ul>
{% endfor %}
</form>
Similarly, if the formset has the ability to order (can_order=True), it is
possible to render it with {{ form.ORDER }}.
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. Let’s take
a look at how this might be accomplished:
from django.forms import formset_factory
from django.shortcuts import render
from myapp.forms import ArticleForm, BookForm
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.
pass
else:
article_formset = ArticleFormSet(prefix='articles')
book_formset = BookFormSet(prefix='books')
return render(request, '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.
Each formset’s prefix replaces the default form
prefix that’s added to each field’s name and id HTML attributes.
Nov 02, 2020