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, 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.

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=[...]) . See also Creating formsets from models with model formsets.

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 . 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 formset_factory() , then max_num will affect validation. See validate_max.

Limiting the maximum number of instantiated forms¶ New in Django Development version. 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' , ... '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. 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 ¶ 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 ¶ 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.

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 . 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'} BaseFormSet also provides an ordering_widget attribute and get_ordering_widget() method that control the widget used with can_order . ordering_widget ¶ BaseFormSet. ordering_widget ¶ Default: 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 ¶ 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 ¶ 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 ModelFormSet , 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 formset.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 ¶ New in Django Development version. 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>

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 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

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: < 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: < 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 use more than one formset in a view.