.. _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 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

display two blank forms::

    >>> 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>`.

.. _formsets-max-num:

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 greater than the number of existing

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.

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 (``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': 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.

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).

.. 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

                pass

        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.

                pass

        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.