.. _formsets: Formsets ======== .. class:: django.forms.formsets.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.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: ... print(form.as_table()) 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) Iterating over the ``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. 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: ... print(form.as_table()) 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 `. .. _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: ... print(form.as_table()) 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 a high limit on the number of forms displayed (1000). In practice this is equivalent to no limit. 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) >>> data = { ... 'form-TOTAL_FORMS': u'1', ... 'form-INITIAL_FORMS': u'0', ... 'form-MAX_NUM_FORMS': u'', ... } >>> 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': u'2', ... 'form-INITIAL_FORMS': u'0', ... 'form-MAX_NUM_FORMS': u'', ... 'form-0-title': u'Test', ... 'form-0-pub_date': u'1904-06-16', ... '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. .. versionadded:: 1.4 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': u'1', ... 'form-INITIAL_FORMS': u'0', ... 'form-MAX_NUM_FORMS': u'', ... 'form-0-title': u'', ... 'form-0-pub_date': u'', ... } >>> 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': 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. 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. 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'1904-06-16', ... 'form-1-title': u'Test', ... 'form-1-pub_date': u'1912-06-23', ... } >>> 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 you 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: ... print(form.as_table()) 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': 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 you create a formset with the ability to select forms for deletion:: >>> 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: .... print(form.as_table()) 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'}] If you are using a :class:`ModelFormSet`, model instances for deleted forms will be deleted when you call ``formset.save()``. 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. 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: ... print(form.as_table()) 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
{{ formset.management_form }} {% for form in formset %} {{ form }} {% endfor %}
However the above can be slightly shortcutted and let the formset itself deal with the management form: .. code-block:: html+django
{{ formset }}
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
{{ formset.management_form }} {% for form in formset %} {{ form.id }}
  • {{ form.title }}
  • {% if formset.can_delete %}
  • {{ form.DELETE }}
  • {% endif %}
{% endfor %}
Similarly, if the formset has the ability to order (``can_order=True``), it is possible to render it with ``{{ form.ORDER }}``. 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.