.. _topics-forms-formsets:
.. _formsets:

Formsets
========

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)

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. 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.

.. seealso::

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

Limiting the maximum number of forms
------------------------------------

The ``max_num`` parameter to ``formset_factory`` gives you the ability to
limit the maximum number of empty 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>

.. versionchanged:: 1.2

If the value of ``max_num`` is geater than the number of existing related
objects, 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``.

A ``max_num`` value of ``None`` (the default) puts no limit on the number of
forms displayed. Please note that the default value of ``max_num`` was changed
from ``0`` to ``None`` in version 1.2 to allow ``0`` as a valid value.

.. versionadded:: 1.2

The dynamic "Add Another" link in the Django admin will not appear if
``max_num`` is less than the number of currently displayed forms.

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::

    >>> 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-MAX_NUM_FORMS': u'',
    ...     '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.

.. _understanding-the-managementform:

Understanding the ManagementForm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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)
    Traceback (most recent call last):
    ...
    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.

.. versionadded:: 1.1

``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.

.. versionadded:: 1.2

``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.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-MAX_NUM_FORMS': u'',
    ...     '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.

Dealing with ordering and deletion of forms
-------------------------------------------

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.

``can_order``
~~~~~~~~~~~~~

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-MAX_NUM_FORMS': u'',
    ...     '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'}

``can_delete``
~~~~~~~~~~~~~~

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" /><input type="hidden" name="form-MAX_NUM_FORMS" id="id_form-MAX_NUM_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-MAX_NUM_FORMS': u'',
    ...     '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'}]

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 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 in views and templates
--------------------------------------

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:

.. code-block:: python

    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:

.. code-block:: html+django

    <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:

.. code-block:: html+django

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

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

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. Lets take
a look at how this might be accomplished:

.. code-block:: python

    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.
