========
Formsets
========

.. currentmodule:: django.forms.formsets

.. class:: BaseFormSet

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,
:func:`~django.forms.formsets.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.

.. _formsets-initial-data:

Using initial data with a formset
=================================

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=[...])``.

.. seealso::

    :ref:`Creating formsets from models with model formsets <model-formsets>`.

.. _formsets-max-num:

Limiting the maximum number of forms
====================================

The ``max_num`` parameter to :func:`~django.forms.formsets.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
:func:`~django.forms.formsets.formset_factory`, then ``max_num`` will affect
validation.  See :ref:`validate_max`.

.. _formsets-absolute-max:

Limiting the maximum number of instantiated forms
=================================================

.. versionadded:: 3.2

The ``absolute_max`` parameter to :func:`.formset_factory` allows limiting the
number of forms that can be instantiated when supplying ``POST`` data. This
protects against memory exhaustion attacks using forged ``POST`` requests::

    >>> from django.forms.formsets import formset_factory
    >>> from myapp.forms import ArticleForm
    >>> ArticleFormSet = formset_factory(ArticleForm, absolute_max=1500)
    >>> data = {
    ...     'form-TOTAL_FORMS': '1501',
    ...     'form-INITIAL_FORMS': '0',
    ...     'form-MAX_NUM_FORMS': '',
    ... }
    >>> formset = ArticleFormSet(data)
    >>> len(formset.forms)
    1500
    >>> formset.is_valid()
    False
    >>> formset.non_form_errors()
    ['Please submit 1000 or fewer forms.']

When ``absolute_max`` is None, it defaults to ``max_num + 1000``. (If
``max_num`` is ``None``, it defaults to ``2000``).

If ``absolute_max`` is less than ``max_num``, a ``ValueError`` will be raised.

Formset validation
==================

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.

.. method:: BaseFormSet.total_error_count()

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

.. _understanding-the-managementform:

Understanding the ``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.core.exceptions.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:

``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.

Custom formset validation
-------------------------

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.core.exceptions import ValidationError
    >>> 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 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.

Validating the number of forms in a 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:

``validate_max``
----------------

If ``validate_max=True`` is passed to
:func:`~django.forms.formsets.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 ``absolute_max``, then the form will fail to validate as if
    ``validate_max`` were set, and additionally only the first ``absolute_max``
    forms will be validated. The remainder will be truncated entirely. This is
    to protect against memory exhaustion attacks using forged POST requests.
    See :ref:`formsets-absolute-max`.

``validate_min``
----------------

If ``validate_min=True`` is passed to
:func:`~django.forms.formsets.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.']

Dealing with ordering and deletion of forms
===========================================

The :func:`~django.forms.formsets.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``
-------------

.. attribute:: 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'}

:class:`~django.forms.formsets.BaseFormSet` also provides an
:attr:`~django.forms.formsets.BaseFormSet.ordering_widget` attribute and
:meth:`~django.forms.formsets.BaseFormSet.get_ordering_widget` method that
control the widget used with
:attr:`~django.forms.formsets.BaseFormSet.can_order`.

``ordering_widget``
^^^^^^^^^^^^^^^^^^^

.. attribute:: BaseFormSet.ordering_widget

Default: :class:`~django.forms.NumberInput`

Set ``ordering_widget`` to specify the widget class to be used with
``can_order``::

    >>> from django.forms import BaseFormSet, formset_factory
    >>> from myapp.forms import ArticleForm
    >>> class BaseArticleFormSet(BaseFormSet):
    ...     ordering_widget = HiddenInput

    >>> ArticleFormSet = formset_factory(ArticleForm, formset=BaseArticleFormSet, can_order=True)

``get_ordering_widget``
^^^^^^^^^^^^^^^^^^^^^^^

.. method:: BaseFormSet.get_ordering_widget()

Override ``get_ordering_widget()`` if you need to provide a widget instance for
use with ``can_order``::

    >>> from django.forms import BaseFormSet, formset_factory
    >>> from myapp.forms import ArticleForm
    >>> class BaseArticleFormSet(BaseFormSet):
    ...     def get_ordering_widget(self):
    ...         return HiddenInput(attrs={'class': 'ordering'})

    >>> ArticleFormSet = formset_factory(ArticleForm, formset=BaseArticleFormSet, can_order=True)

``can_delete``
--------------

.. attribute:: 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 :class:`ModelFormSet<django.forms.models.BaseModelFormSet>`,
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
:attr:`formset.deleted_objects
<django.forms.models.BaseModelFormSet.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.

``can_delete_extra``
--------------------

.. versionadded:: 3.2

.. attribute:: BaseFormSet.can_delete_extra

Default: ``True``

While setting ``can_delete=True``, specifying ``can_delete_extra=False`` will
remove the option to delete extra forms.

Adding additional fields to a formset
=====================================

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 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>

.. _custom-formset-form-kwargs:

Passing custom parameters to formset forms
==========================================

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
:ref:`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

.. _formset-prefix:

Customizing a formset's prefix
==============================

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:

.. code-block:: html

    <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:

.. code-block:: html

    <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 :ref:`use more than one formset in a view
<multiple-formsets-in-view>`.

Using a formset in views and templates
======================================

Using a formset inside a view is not very different from 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:

.. code-block:: html+django

    <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:

.. code-block:: html+django

    <form method="post">
        <table>
            {{ formset }}
        </table>
    </form>

The above ends up calling the ``as_table`` method on the formset class.

.. _manually-rendered-can-delete-and-can-order:

Manually rendered ``can_delete`` and ``can_order``
--------------------------------------------------

If you manually render fields in the template, you can render
``can_delete`` parameter with ``{{ form.DELETE }}``:

.. code-block:: html+django

    <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 }}``.

.. _multiple-formsets-in-view:

Using more than one formset in a view
-------------------------------------

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 :ref:`prefix <formset-prefix>` replaces the default ``form``
prefix that's added to each field's ``name`` and ``id`` HTML attributes.
