Formsets | Django documentation (original) (raw)

class BaseFormSet[source]

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) ...

Title:
Pub date:

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)

Formsets can be iterated and indexed, accessing forms in the order they were created. You can reorder the forms by overriding the defaultiteration andindexing behavior if needed.

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) ...

Title:
Pub date:
Title:
Pub date:
Title:
Pub date:

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 sameinitial 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=[...]).

Limiting the maximum number of forms

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) ...

Title:
Pub date:

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=1and 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 theformset_factory(), then max_num will affect validation. See validate_max.

Limiting the maximum number of instantiated forms

The absolute_max parameter to 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", ... } formset = ArticleFormSet(data) len(formset.forms) 1500 formset.is_valid() False formset.non_form_errors() ['Please submit at most 1000 forms.']

When absolute_max is None, it defaults to max_num + 1000. (Ifmax_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", ... } 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-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.

BaseFormSet.total_error_count()[source]

To check how many errors there are in the formset, we can use thetotal_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-0-title": "", ... "form-0-pub_date": "", ... } formset = ArticleFormSet(data) formset.has_changed() False

Understanding the ManagementForm

You may have noticed the additional data (form-TOTAL_FORMS,form-INITIAL_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, the formset will be invalid:

data = { ... "form-0-title": "Test", ... "form-0-pub_date": "", ... } formset = ArticleFormSet(data) formset.is_valid() False

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 POSTdata. 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).

Note

As well as the form-TOTAL_FORMS and form-INITIAL_FORMS fields shown in the examples here, the management form also includesform-MIN_NUM_FORMS and form-MAX_NUM_FORMS fields. They are output with the rest of the management form, but only for the convenience of client-side code. These fields are not required and so are not shown in the example POST data.

total_form_count and initial_form_count

BaseFormSet has a couple of methods that are closely related to theManagementForm, 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.

error_messages

The error_messages argument lets you override the default messages that the formset will raise. Pass in a dictionary with keys matching the error messages you want to override. Error message keys include 'too_few_forms','too_many_forms', and 'missing_management_form'. The'too_few_forms' and 'too_many_forms' error messages may contain%(num)d, which will be replaced with min_num and max_num, respectively.

For example, here is the default error message when the management form is missing:

formset = ArticleFormSet({}) formset.is_valid() False formset.non_form_errors() ['ManagementForm data is missing or has been tampered with. Missing fields: form-TOTAL_FORMS, form-INITIAL_FORMS. You may need to file a bug report if the issue persists.']

And here is a custom error message:

formset = ArticleFormSet( ... {}, error_messages={"missing_management_form": "Sorry, something went wrong."} ... ) formset.is_valid() False formset.non_form_errors() ['Sorry, something went wrong.']

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 = set() ... 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.add(title) ...

ArticleFormSet = formset_factory(ArticleForm, formset=BaseArticleFormSet) data = { ... "form-TOTAL_FORMS": "2", ... "form-INITIAL_FORMS": "0", ... "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.

Non-form errors will be rendered with an additional class of nonform to help distinguish them from form-specific errors. For example,{{ formset.non_form_errors }} would look like:

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

If validate_max=True is passed toformset_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-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 at most 1 form.']

validate_max=True validates against max_num strictly even ifmax_num was exceeded because the amount of initial data supplied was excessive.

The error message can be customized by passing the 'too_many_forms' message to the error_messages argument.

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 ifvalidate_max were set, and additionally only the first absolute_maxforms will be validated. The remainder will be truncated entirely. This is to protect against memory exhaustion attacks using forged POST requests. See Limiting the maximum number of instantiated forms.

validate_min

If validate_min=True is passed toformset_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-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 at least 3 forms.']

The error message can be customized by passing the 'too_few_forms' message to the error_messages argument.

Note

Regardless of validate_min, if a formset contains no data, thenextra + min_num empty forms will be displayed.

Dealing with ordering and deletion of 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) ...

Title:
Pub date:
Order:
Title:
Pub date:
Order:
Title:
Pub date:
Order:

This adds an additional field to each form. This new field is named ORDERand 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-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)}, ... ], ... ) for form in formset.ordered_forms: ... print(form.cleaned_data) ... {'title': 'Article #3', 'pub_date': datetime.date(2008, 5, 1), 'ORDER': 0} {'title': 'Article #2', 'pub_date': datetime.date(2008, 5, 11), 'ORDER': 1} {'title': 'Article #1', 'pub_date': datetime.date(2008, 5, 10), 'ORDER': 2}

BaseFormSet also provides anordering_widget attribute andget_ordering_widget() method that control the widget used withcan_order.

ordering_widget

BaseFormSet.ordering_widget

Default: NumberInput

Set ordering_widget to specify the widget class to be used withcan_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

BaseFormSet.get_ordering_widget()[source]

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

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) ...

Title:
Pub date:
Delete:
Title:
Pub date:
Delete:
Title:
Pub date:
Delete:

Similar to can_order this adds a new field to each form named DELETEand 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-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] [{'title': 'Article #1', 'pub_date': datetime.date(2008, 5, 10), 'DELETE': True}]

If you are using a ModelFormSet, model instances for deleted forms will be deleted when you callformset.save().

If you call formset.save(commit=False), objects will not be deleted automatically. You’ll need to call delete() on each of theformset.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.

BaseFormSet also provides adeletion_widget attribute andget_deletion_widget() method that control the widget used withcan_delete.

deletion_widget

BaseFormSet.deletion_widget

Default: CheckboxInput

Set deletion_widget to specify the widget class to be used withcan_delete:

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

ArticleFormSet = formset_factory( ... ArticleForm, formset=BaseArticleFormSet, can_delete=True ... )

get_deletion_widget

BaseFormSet.get_deletion_widget()[source]

Override get_deletion_widget() if you need to provide a widget instance for use with can_delete:

from django.forms import BaseFormSet, formset_factory from myapp.forms import ArticleForm class BaseArticleFormSet(BaseFormSet): ... def get_deletion_widget(self): ... return HiddenInput(attrs={"class": "deletion"}) ...

ArticleFormSet = formset_factory( ... ArticleForm, formset=BaseArticleFormSet, can_delete=True ... )

can_delete_extra

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) ...

Title:
Pub date:
My field:

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 theempty_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 ...

ArticleFormSet = formset_factory(MyArticleForm, formset=BaseArticleFormSet) formset = ArticleFormSet()

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’sprefix argument.

For example, in the default case, you might see:

Title:

But with ArticleFormset(prefix='article') that becomes:

Title:

This is useful if you want to use more than one formset in a view.

Using a formset in views and templates

Formsets have the following attributes and methods associated with rendering:

BaseFormSet.renderer

Specifies the renderer to use for the formset. Defaults to the renderer specified by the FORM_RENDERERsetting.

BaseFormSet.template_name[source]

The name of the template rendered if the formset is cast into a string, e.g. via print(formset) or in a template via {{ formset }}.

By default, a property returning the value of the renderer’sformset_template_name. You may set it as a string template name in order to override that for a particular formset class.

This template will be used to render the formset’s management form, and then each form in the formset as per the template defined by the form’stemplate_name.

BaseFormSet.template_name_div

The name of the template used when calling as_div(). By default this is "django/forms/formsets/div.html". This template renders the formset’s management form and then each form in the formset as per the form’s as_div() method.

BaseFormSet.template_name_p

The name of the template used when calling as_p(). By default this is "django/forms/formsets/p.html". This template renders the formset’s management form and then each form in the formset as per the form’sas_p() method.

BaseFormSet.template_name_table

The name of the template used when calling as_table(). By default this is "django/forms/formsets/table.html". This template renders the formset’s management form and then each form in the formset as per the form’s as_table() method.

BaseFormSet.template_name_ul

The name of the template used when calling as_ul(). By default this is "django/forms/formsets/ul.html". This template renders the formset’s management form and then each form in the formset as per the form’sas_ul() method.

BaseFormSet.get_context()[source]

Returns the context for rendering a formset in a template.

The available context is:

BaseFormSet.render(template_name=None, context=None, renderer=None)

The render method is called by __str__ as well as the as_div(),as_p(), as_ul(), and as_table() methods. All arguments are optional and will default to:

BaseFormSet.as_div()

Renders the formset with the template_name_div template.

BaseFormSet.as_p()

Renders the formset with the template_name_p template.

BaseFormSet.as_table()

Renders the formset with the template_name_table template.

BaseFormSet.as_ul()

Renders the formset with the template_name_ul template.

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

{{ formset.management_form }} {% for form in formset %} {{ form }} {% endfor %}

However there’s a slight shortcut for the above by letting the formset itself deal with the management form:

{{ formset }}

The above ends up calling the BaseFormSet.render() method on the formset class. This renders the formset using the template specified by thetemplate_name attribute. Similar to forms, by default the formset will be rendered as_div, with other helper methods of as_p,as_ul, and as_table being available. The rendering of the formset can be customized by specifying the template_name attribute, or more generally by overriding the default template.

Manually rendered can_delete and can_order

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

{{ formset.management_form }} {% for form in formset %} {% 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 useprefix 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 formprefix that’s added to each field’s name and id HTML attributes.