ModelForm¶ModelForm¶If you’re building a database-driven app, chances are you’ll have forms that
map closely to Django models. For instance, you might have a BlogComment
model, and you want to create a form that lets people submit comments. In this
case, it would be redundant to define the field types in your form, because
you’ve already defined the fields in your model.
For this reason, Django provides a helper class that lets you create a Form
class from a Django model.
For example:
>>> from django.forms import ModelForm
>>> from myapp.models import Article
# Create the form class.
>>> class ArticleForm(ModelForm):
... class Meta:
... model = Article
... fields = ['pub_date', 'headline', 'content', 'reporter']
# Creating a form to add an article.
>>> form = ArticleForm()
# Creating a form to change an existing article.
>>> article = Article.objects.get(pk=1)
>>> form = ArticleForm(instance=article)
The generated Form class will have a form field for every model field
specified, in the order specified in the fields attribute.
Each model field has a corresponding default form field. For example, a
CharField on a model is represented as a CharField on a form. A model
ManyToManyField is represented as a MultipleChoiceField. Here is the
full list of conversions:
As you might expect, the ForeignKey and ManyToManyField model field
types are special cases:
ForeignKey is represented by django.forms.ModelChoiceField,
which is a ChoiceField whose choices are a model QuerySet.ManyToManyField is represented by
django.forms.ModelMultipleChoiceField, which is a
MultipleChoiceField whose choices are a model QuerySet.In addition, each generated form field has attributes set as follows:
blank=True, then required is set to
False on the form field. Otherwise, required=True.label is set to the verbose_name of the model
field, with the first character capitalized.help_text is set to the help_text of the model
field.choices set, then the form field’s widget
will be set to Select, with choices coming from the model field’s
choices. The choices will normally include the blank choice which is
selected by default. If the field is required, this forces the user to
make a selection. The blank choice will not be included if the model
field has blank=False and an explicit default value (the
default value will be initially selected instead).Finally, note that you can override the form field used for a given model field. See Overriding the default fields below.
Consider this set of models:
from django.db import models
from django.forms import ModelForm
TITLE_CHOICES = [
('MR', 'Mr.'),
('MRS', 'Mrs.'),
('MS', 'Ms.'),
]
class Author(models.Model):
name = models.CharField(max_length=100)
title = models.CharField(max_length=3, choices=TITLE_CHOICES)
birth_date = models.DateField(blank=True, null=True)
def __str__(self):
return self.name
class Book(models.Model):
name = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
class AuthorForm(ModelForm):
class Meta:
model = Author
fields = ['name', 'title', 'birth_date']
class BookForm(ModelForm):
class Meta:
model = Book
fields = ['name', 'authors']
With these models, the ModelForm subclasses above would be roughly
equivalent to this (the only difference being the save() method, which
we’ll discuss in a moment.):
from django import forms
class AuthorForm(forms.Form):
name = forms.CharField(max_length=100)
title = forms.CharField(
max_length=3,
widget=forms.Select(choices=TITLE_CHOICES),
)
birth_date = forms.DateField(required=False)
class BookForm(forms.Form):
name = forms.CharField(max_length=100)
authors = forms.ModelMultipleChoiceField(queryset=Author.objects.all())
ModelForm¶There are two main steps involved in validating a ModelForm:
Just like normal form validation, model form validation is triggered implicitly
when calling is_valid() or accessing the
errors attribute and explicitly when calling
full_clean(), although you will typically not use the latter method in
practice.
Model validation (Model.full_clean()) is triggered from within the form
validation step, right after the form’s clean() method is called.
Warning
The cleaning process modifies the model instance passed to the
ModelForm constructor in various ways. For instance, any date fields on
the model are converted into actual date objects. Failed validation may
leave the underlying model instance in an inconsistent state and therefore
it’s not recommended to reuse it.
You can override the clean() method on a model form to provide additional
validation in the same way you can on a normal form.
A model form instance attached to a model object will contain an instance
attribute that gives its methods access to that specific model instance.
Warning
The ModelForm.clean() method sets a flag that makes the model
validation step validate the uniqueness of model
fields that are marked as unique, unique_together or
unique_for_date|month|year.
If you would like to override the clean() method and maintain this
validation, you must call the parent class’s clean() method.
As part of the validation process, ModelForm will call the clean()
method of each field on your model that has a corresponding field on your form.
If you have excluded any model fields, validation will not be run on those
fields. See the form validation documentation
for more on how field cleaning and validation work.
The model’s clean() method will be called before any uniqueness checks are
made. See Validating objects for more information
on the model’s clean() hook.
error_messages¶Error messages defined at the
form field level or at the
form Meta level always take
precedence over the error messages defined at the
model field level.
Error messages defined on model fields are only used when the
ValidationError is raised during the model validation step and no corresponding error messages are defined at
the form level.
You can override the error messages from NON_FIELD_ERRORS raised by model
validation by adding the NON_FIELD_ERRORS key
to the error_messages dictionary of the ModelForm’s inner Meta class:
from django.core.exceptions import NON_FIELD_ERRORS
from django.forms import ModelForm
class ArticleForm(ModelForm):
class Meta:
error_messages = {
NON_FIELD_ERRORS: {
'unique_together': "%(model_name)s's %(field_labels)s are not unique.",
}
}
save() method¶Every ModelForm also has a save() method. This method creates and saves
a database object from the data bound to the form. A subclass of ModelForm
can accept an existing model instance as the keyword argument instance; if
this is supplied, save() will update that instance. If it’s not supplied,
save() will create a new instance of the specified model:
>>> from myapp.models import Article
>>> from myapp.forms import ArticleForm
# Create a form instance from POST data.
>>> f = ArticleForm(request.POST)
# Save a new Article object from the form's data.
>>> new_article = f.save()
# Create a form to edit an existing Article, but use
# POST data to populate the form.
>>> a = Article.objects.get(pk=1)
>>> f = ArticleForm(request.POST, instance=a)
>>> f.save()
Note that if the form hasn’t been validated, calling save() will do so by checking
form.errors. A ValueError will be raised if the data in the form
doesn’t validate – i.e., if form.errors evaluates to True.
If an optional field doesn’t appear in the form’s data, the resulting model
instance uses the model field default, if
there is one, for that field. This behavior doesn’t apply to fields that use
CheckboxInput,
CheckboxSelectMultiple, or
SelectMultiple (or any custom widget whose
value_omitted_from_data() method always returns
False) since an unchecked checkbox and unselected <select multiple>
don’t appear in the data of an HTML form submission. Use a custom form field or
widget if you’re designing an API and want the default fallback behavior for a
field that uses one of these widgets.
This save() method accepts an optional commit keyword argument, which
accepts either True or False. If you call save() with
commit=False, then it will return an object that hasn’t yet been saved to
the database. In this case, it’s up to you to call save() on the resulting
model instance. This is useful if you want to do custom processing on the
object before saving it, or if you want to use one of the specialized
model saving options. commit is True
by default.
Another side effect of using commit=False is seen when your model has
a many-to-many relation with another model. If your model has a many-to-many
relation and you specify commit=False when you save a form, Django cannot
immediately save the form data for the many-to-many relation. This is because
it isn’t possible to save many-to-many data for an instance until the instance
exists in the database.
To work around this problem, every time you save a form using commit=False,
Django adds a save_m2m() method to your ModelForm subclass. After
you’ve manually saved the instance produced by the form, you can invoke
save_m2m() to save the many-to-many form data. For example:
# Create a form instance with POST data.
>>> f = AuthorForm(request.POST)
# Create, but don't save the new author instance.
>>> new_author = f.save(commit=False)
# Modify the author in some way.
>>> new_author.some_field = 'some_value'
# Save the new instance.
>>> new_author.save()
# Now, save the many-to-many data for the form.
>>> f.save_m2m()
Calling save_m2m() is only required if you use save(commit=False).
When you use a save() on a form, all data – including many-to-many data –
is saved without the need for any additional method calls. For example:
# Create a form instance with POST data.
>>> a = Author()
>>> f = AuthorForm(request.POST, instance=a)
# Create and save the new author instance. There's no need to do anything else.
>>> new_author = f.save()
Other than the save() and save_m2m() methods, a ModelForm works
exactly the same way as any other forms form. For example, the
is_valid() method is used to check for validity, the is_multipart()
method is used to determine whether a form requires multipart file upload (and
hence whether request.FILES must be passed to the form), etc. See
Binding uploaded files to a form for more information.
It is strongly recommended that you explicitly set all fields that should be
edited in the form using the fields attribute. Failure to do so can easily
lead to security problems when a form unexpectedly allows a user to set certain
fields, especially when new fields are added to a model. Depending on how the
form is rendered, the problem may not even be visible on the web page.
The alternative approach would be to include all fields automatically, or remove only some. This fundamental approach is known to be much less secure and has led to serious exploits on major websites (e.g. GitHub).
There are, however, two shortcuts available for cases where you can guarantee these security concerns do not apply to you:
Set the fields attribute to the special value '__all__' to indicate
that all fields in the model should be used. For example:
from django.forms import ModelForm
class AuthorForm(ModelForm):
class Meta:
model = Author
fields = '__all__'
Set the exclude attribute of the ModelForm’s inner Meta class to
a list of fields to be excluded from the form.
For example:
class PartialAuthorForm(ModelForm):
class Meta:
model = Author
exclude = ['title']
Since the Author model has the 3 fields name, title and
birth_date, this will result in the fields name and birth_date
being present on the form.
If either of these are used, the order the fields appear in the form will be the
order the fields are defined in the model, with ManyToManyField instances
appearing last.
In addition, Django applies the following rule: if you set editable=False on
the model field, any form created from the model via ModelForm will not
include that field.
Note
Any fields not included in a form by the above logic
will not be set by the form’s save() method. Also, if you
manually add the excluded fields back to the form, they will not
be initialized from the model instance.
Django will prevent any attempt to save an incomplete model, so if
the model does not allow the missing fields to be empty, and does
not provide a default value for the missing fields, any attempt to
save() a ModelForm with missing fields will fail. To
avoid this failure, you must instantiate your model with initial
values for the missing, but required fields:
author = Author(title='Mr')
form = PartialAuthorForm(request.POST, instance=author)
form.save()
Alternatively, you can use save(commit=False) and manually set
any extra required fields:
form = PartialAuthorForm(request.POST)
author = form.save(commit=False)
author.title = 'Mr'
author.save()
See the section on saving forms for more details on using
save(commit=False).
The default field types, as described in the Field types table above, are
sensible defaults. If you have a DateField in your model, chances are you’d
want that to be represented as a DateField in your form. But ModelForm
gives you the flexibility of changing the form field for a given model.
To specify a custom widget for a field, use the widgets attribute of the
inner Meta class. This should be a dictionary mapping field names to widget
classes or instances.
For example, if you want the CharField for the name attribute of
Author to be represented by a <textarea> instead of its default
<input type="text">, you can override the field’s widget:
from django.forms import ModelForm, Textarea
from myapp.models import Author
class AuthorForm(ModelForm):
class Meta:
model = Author
fields = ('name', 'title', 'birth_date')
widgets = {
'name': Textarea(attrs={'cols': 80, 'rows': 20}),
}
The widgets dictionary accepts either widget instances (e.g.,
Textarea(...)) or classes (e.g., Textarea). Note that the widgets
dictionary is ignored for a model field with a non-empty choices attribute.
In this case, you must override the form field to use a different widget.
Similarly, you can specify the labels, help_texts and error_messages
attributes of the inner Meta class if you want to further customize a field.
For example if you wanted to customize the wording of all user facing strings for
the name field:
from django.utils.translation import gettext_lazy as _
class AuthorForm(ModelForm):
class Meta:
model = Author
fields = ('name', 'title', 'birth_date')
labels = {
'name': _('Writer'),
}
help_texts = {
'name': _('Some useful help text.'),
}
error_messages = {
'name': {
'max_length': _("This writer's name is too long."),
},
}
You can also specify field_classes to customize the type of fields
instantiated by the form.
For example, if you wanted to use MySlugFormField for the slug
field, you could do the following:
from django.forms import ModelForm
from myapp.models import Article
class ArticleForm(ModelForm):
class Meta:
model = Article
fields = ['pub_date', 'headline', 'content', 'reporter', 'slug']
field_classes = {
'slug': MySlugFormField,
}
Finally, if you want complete control over of a field – including its type,
validators, required, etc. – you can do this by declaratively specifying
fields like you would in a regular Form.
If you want to specify a field’s validators, you can do so by defining
the field declaratively and setting its validators parameter:
from django.forms import CharField, ModelForm
from myapp.models import Article
class ArticleForm(ModelForm):
slug = CharField(validators=[validate_slug])
class Meta:
model = Article
fields = ['pub_date', 'headline', 'content', 'reporter', 'slug']
Note
When you explicitly instantiate a form field like this, it is important to
understand how ModelForm and regular Form are related.
ModelForm is a regular Form which can automatically generate
certain fields. The fields that are automatically generated depend on
the content of the Meta class and on which fields have already been
defined declaratively. Basically, ModelForm will only generate fields
that are missing from the form, or in other words, fields that weren’t
defined declaratively.
Fields defined declaratively are left as-is, therefore any customizations
made to Meta attributes such as widgets, labels, help_texts,
or error_messages are ignored; these only apply to fields that are
generated automatically.
Similarly, fields defined declaratively do not draw their attributes like
max_length or required from the corresponding model. If you want to
maintain the behavior specified in the model, you must set the relevant
arguments explicitly when declaring the form field.
For example, if the Article model looks like this:
class Article(models.Model):
headline = models.CharField(
max_length=200,
null=True,
blank=True,
help_text='Use puns liberally',
)
content = models.TextField()
and you want to do some custom validation for headline, while keeping
the blank and help_text values as specified, you might define
ArticleForm like this:
class ArticleForm(ModelForm):
headline = MyFormField(
max_length=200,
required=False,
help_text='Use puns liberally',
)
class Meta:
model = Article
fields = ['headline', 'content']
You must ensure that the type of the form field can be used to set the
contents of the corresponding model field. When they are not compatible,
you will get a ValueError as no implicit conversion takes place.
See the form field documentation for more information on fields and their arguments.
By default, the fields in a ModelForm will not localize their data. To
enable localization for fields, you can use the localized_fields
attribute on the Meta class.
>>> from django.forms import ModelForm
>>> from myapp.models import Author
>>> class AuthorForm(ModelForm):
... class Meta:
... model = Author
... localized_fields = ('birth_date',)
If localized_fields is set to the special value '__all__', all fields
will be localized.
As with basic forms, you can extend and reuse ModelForms by inheriting
them. This is useful if you need to declare extra fields or extra methods on a
parent class for use in a number of forms derived from models. For example,
using the previous ArticleForm class:
>>> class EnhancedArticleForm(ArticleForm):
... def clean_pub_date(self):
... ...
This creates a form that behaves identically to ArticleForm, except there’s
some extra validation and cleaning for the pub_date field.
You can also subclass the parent’s Meta inner class if you want to change
the Meta.fields or Meta.exclude lists:
>>> class RestrictedArticleForm(EnhancedArticleForm):
... class Meta(ArticleForm.Meta):
... exclude = ('body',)
This adds the extra method from the EnhancedArticleForm and modifies
the original ArticleForm.Meta to remove one field.
There are a couple of things to note, however.
Normal Python name resolution rules apply. If you have multiple base
classes that declare a Meta inner class, only the first one will be
used. This means the child’s Meta, if it exists, otherwise the
Meta of the first parent, etc.
It’s possible to inherit from both Form and ModelForm simultaneously,
however, you must ensure that ModelForm appears first in the MRO. This is
because these classes rely on different metaclasses and a class can only have
one metaclass.
It’s possible to declaratively remove a Field inherited from a parent class by
setting the name to be None on the subclass.
You can only use this technique to opt out from a field defined declaratively
by a parent class; it won’t prevent the ModelForm metaclass from generating
a default field. To opt-out from default fields, see
Selecting the fields to use.
As with regular forms, it’s possible to specify initial data for forms by
specifying an initial parameter when instantiating the form. Initial
values provided this way will override both initial values from the form field
and values from an attached model instance. For example:
>>> article = Article.objects.get(pk=1)
>>> article.headline
'My headline'
>>> form = ArticleForm(initial={'headline': 'Initial headline'}, instance=article)
>>> form['headline'].value()
'Initial headline'
You can create forms from a given model using the standalone function
modelform_factory(), instead of using a class
definition. This may be more convenient if you do not have many customizations
to make:
>>> from django.forms import modelform_factory
>>> from myapp.models import Book
>>> BookForm = modelform_factory(Book, fields=("author", "title"))
This can also be used to make modifications to existing forms, for example by specifying the widgets to be used for a given field:
>>> from django.forms import Textarea
>>> Form = modelform_factory(Book, form=BookForm,
... widgets={"title": Textarea()})
The fields to include can be specified using the fields and exclude
keyword arguments, or the corresponding attributes on the ModelForm inner
Meta class. Please see the ModelForm Selecting the fields to use
documentation.
… or enable localization for specific fields:
>>> Form = modelform_factory(Author, form=AuthorForm, localized_fields=("birth_date",))
models.BaseModelFormSet¶Like regular formsets, Django provides a couple
of enhanced formset classes to make working with Django models more
convenient. Let’s reuse the Author model from above:
>>> from django.forms import modelformset_factory
>>> from myapp.models import Author
>>> AuthorFormSet = modelformset_factory(Author, fields=('name', 'title'))
Using fields restricts the formset to use only the given fields.
Alternatively, you can take an “opt-out” approach, specifying which fields to
exclude:
>>> AuthorFormSet = modelformset_factory(Author, exclude=('birth_date',))
This will create a formset that is capable of working with the data associated
with the Author model. It works just like a regular formset:
>>> formset = AuthorFormSet()
>>> print(formset)
<input type="hidden" name="form-TOTAL_FORMS" value="1" id="id_form-TOTAL_FORMS"><input type="hidden" name="form-INITIAL_FORMS" value="0" id="id_form-INITIAL_FORMS"><input type="hidden" name="form-MIN_NUM_FORMS" value="0" id="id_form-MIN_NUM_FORMS"><input type="hidden" name="form-MAX_NUM_FORMS" value="1000" id="id_form-MAX_NUM_FORMS">
<tr><th><label for="id_form-0-name">Name:</label></th><td><input id="id_form-0-name" type="text" name="form-0-name" maxlength="100"></td></tr>
<tr><th><label for="id_form-0-title">Title:</label></th><td><select name="form-0-title" id="id_form-0-title">
<option value="" selected>---------</option>
<option value="MR">Mr.</option>
<option value="MRS">Mrs.</option>
<option value="MS">Ms.</option>
</select><input type="hidden" name="form-0-id" id="id_form-0-id"></td></tr>
Note
modelformset_factory() uses
formset_factory() to generate formsets. This
means that a model formset is an extension of a basic formset that knows
how to interact with a particular model.
Note
When using multi-table inheritance, forms
generated by a formset factory will contain a parent link field (by default
<parent_model_name>_ptr) instead of an id field.
By default, when you create a formset from a model, the formset will use a
queryset that includes all objects in the model (e.g.,
Author.objects.all()). You can override this behavior by using the
queryset argument:
>>> formset = AuthorFormSet(queryset=Author.objects.filter(name__startswith='O'))
Alternatively, you can create a subclass that sets self.queryset in
__init__:
from django.forms import BaseModelFormSet
from myapp.models import Author
class BaseAuthorFormSet(BaseModelFormSet):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.queryset = Author.objects.filter(name__startswith='O')
Then, pass your BaseAuthorFormSet class to the factory function:
>>> AuthorFormSet = modelformset_factory(
... Author, fields=('name', 'title'), formset=BaseAuthorFormSet)
If you want to return a formset that doesn’t include any pre-existing instances of the model, you can specify an empty QuerySet:
>>> AuthorFormSet(queryset=Author.objects.none())
By default, when you use modelformset_factory, a model form will
be created using modelform_factory().
Often, it can be useful to specify a custom model form. For example,
you can create a custom model form that has custom validation:
class AuthorForm(forms.ModelForm):
class Meta:
model = Author
fields = ('name', 'title')
def clean_name(self):
# custom validation for the name field
...
Then, pass your model form to the factory function:
AuthorFormSet = modelformset_factory(Author, form=AuthorForm)
It is not always necessary to define a custom model form. The
modelformset_factory function has several arguments which are
passed through to modelform_factory, which are described below.
widgets¶Using the widgets parameter, you can specify a dictionary of values to
customize the ModelForm’s widget class for a particular field. This
works the same way as the widgets dictionary on the inner Meta
class of a ModelForm works:
>>> AuthorFormSet = modelformset_factory(
... Author, fields=('name', 'title'),
... widgets={'name': Textarea(attrs={'cols': 80, 'rows': 20})})
localized_fields¶Using the localized_fields parameter, you can enable localization for
fields in the form.
>>> AuthorFormSet = modelformset_factory(
... Author, fields=('name', 'title', 'birth_date'),
... localized_fields=('birth_date',))
If localized_fields is set to the special value '__all__', all fields
will be localized.
As with regular formsets, it’s possible to specify initial data for forms in the formset by specifying an initial
parameter when instantiating the model formset class returned by
modelformset_factory(). However, with model
formsets, the initial values only apply to extra forms, those that aren’t
attached to an existing model instance. If the length of initial exceeds
the number of extra forms, the excess initial data is ignored. If the extra
forms with initial data aren’t changed by the user, they won’t be validated or
saved.
As with a ModelForm, you can save the data as a model object. This is done
with the formset’s save() method:
# Create a formset instance with POST data.
>>> formset = AuthorFormSet(request.POST)
# Assuming all is valid, save the data.
>>> instances = formset.save()
The save() method returns the instances that have been saved to the
database. If a given instance’s data didn’t change in the bound data, the
instance won’t be saved to the database and won’t be included in the return
value (instances, in the above example).
When fields are missing from the form (for example because they have been
excluded), these fields will not be set by the save() method. You can find
more information about this restriction, which also holds for regular
ModelForms, in Selecting the fields to use.
Pass commit=False to return the unsaved model instances:
# don't save to the database
>>> instances = formset.save(commit=False)
>>> for instance in instances:
... # do something with instance
... instance.save()
This gives you the ability to attach data to the instances before saving them
to the database. If your formset contains a ManyToManyField, you’ll also
need to call formset.save_m2m() to ensure the many-to-many relationships
are saved properly.
After calling save(), your model formset will have three new attributes
containing the formset’s changes:
models.BaseModelFormSet.changed_objects¶models.BaseModelFormSet.deleted_objects¶models.BaseModelFormSet.new_objects¶As with regular formsets, you can use the max_num and extra parameters
to modelformset_factory() to limit the number of
extra forms displayed.
max_num does not prevent existing objects from being displayed:
>>> Author.objects.order_by('name')
<QuerySet [<Author: Charles Baudelaire>, <Author: Paul Verlaine>, <Author: Walt Whitman>]>
>>> AuthorFormSet = modelformset_factory(Author, fields=('name',), max_num=1)
>>> formset = AuthorFormSet(queryset=Author.objects.order_by('name'))
>>> [x.name for x in formset.get_queryset()]
['Charles Baudelaire', 'Paul Verlaine', 'Walt Whitman']
Also, extra=0 doesn’t prevent creation of new model instances as you can
add additional forms with JavaScript
or send additional POST data. Formsets don’t yet provide functionality for an “edit only” view that prevents creation of new instances.
If the value of max_num is greater 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:
>>> AuthorFormSet = modelformset_factory(Author, fields=('name',), max_num=4, extra=2)
>>> formset = AuthorFormSet(queryset=Author.objects.order_by('name'))
>>> for form in formset:
... print(form.as_table())
<tr><th><label for="id_form-0-name">Name:</label></th><td><input id="id_form-0-name" type="text" name="form-0-name" value="Charles Baudelaire" maxlength="100"><input type="hidden" name="form-0-id" value="1" id="id_form-0-id"></td></tr>
<tr><th><label for="id_form-1-name">Name:</label></th><td><input id="id_form-1-name" type="text" name="form-1-name" value="Paul Verlaine" maxlength="100"><input type="hidden" name="form-1-id" value="3" id="id_form-1-id"></td></tr>
<tr><th><label for="id_form-2-name">Name:</label></th><td><input id="id_form-2-name" type="text" name="form-2-name" value="Walt Whitman" maxlength="100"><input type="hidden" name="form-2-id" value="2" id="id_form-2-id"></td></tr>
<tr><th><label for="id_form-3-name">Name:</label></th><td><input id="id_form-3-name" type="text" name="form-3-name" maxlength="100"><input type="hidden" name="form-3-id" id="id_form-3-id"></td></tr>
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.
Model formsets are very similar to formsets. Let’s say we want to present a
formset to edit Author model instances:
from django.forms import modelformset_factory
from django.shortcuts import render
from myapp.models import Author
def manage_authors(request):
AuthorFormSet = modelformset_factory(Author, fields=('name', 'title'))
if request.method == 'POST':
formset = AuthorFormSet(request.POST, request.FILES)
if formset.is_valid():
formset.save()
# do something.
else:
formset = AuthorFormSet()
return render(request, 'manage_authors.html', {'formset': formset})
As you can see, the view logic of a model formset isn’t drastically different
than that of a “normal” formset. The only difference is that we call
formset.save() to save the data into the database. (This was described
above, in Saving objects in the formset.)
clean() on a ModelFormSet¶Just like with ModelForms, by default the clean() method of a
ModelFormSet will validate that none of the items in the formset violate
the unique constraints on your model (either unique, unique_together or
unique_for_date|month|year). If you want to override the clean() method
on a ModelFormSet and maintain this validation, you must call the parent
class’s clean method:
from django.forms import BaseModelFormSet
class MyModelFormSet(BaseModelFormSet):
def clean(self):
super().clean()
# example custom validation across forms in the formset
for form in self.forms:
# your custom formset validation
...
Also note that by the time you reach this step, individual model instances
have already been created for each Form. Modifying a value in
form.cleaned_data is not sufficient to affect the saved value. If you wish
to modify a value in ModelFormSet.clean() you must modify
form.instance:
from django.forms import BaseModelFormSet
class MyModelFormSet(BaseModelFormSet):
def clean(self):
super().clean()
for form in self.forms:
name = form.cleaned_data['name'].upper()
form.cleaned_data['name'] = name
# update the instance value.
form.instance.name = name
As stated earlier, you can override the default queryset used by the model formset:
from django.forms import modelformset_factory
from django.shortcuts import render
from myapp.models import Author
def manage_authors(request):
AuthorFormSet = modelformset_factory(Author, fields=('name', 'title'))
if request.method == "POST":
formset = AuthorFormSet(
request.POST, request.FILES,
queryset=Author.objects.filter(name__startswith='O'),
)
if formset.is_valid():
formset.save()
# Do something.
else:
formset = AuthorFormSet(queryset=Author.objects.filter(name__startswith='O'))
return render(request, 'manage_authors.html', {'formset': formset})
Note that we pass the queryset argument in both the POST and GET
cases in this example.
There are three ways to render a formset in a Django template.
First, you can let the formset do most of the work:
<form method="post">
{{ formset }}
</form>
Second, you can manually render the formset, but let the form deal with itself:
<form method="post">
{{ formset.management_form }}
{% for form in formset %}
{{ form }}
{% endfor %}
</form>
When you manually render the forms yourself, be sure to render the management form as shown above. See the management form documentation.
Third, you can manually render each field:
<form method="post">
{{ formset.management_form }}
{% for form in formset %}
{% for field in form %}
{{ field.label_tag }} {{ field }}
{% endfor %}
{% endfor %}
</form>
If you opt to use this third method and you don’t iterate over the fields with
a {% for %} loop, you’ll need to render the primary key field. For example,
if you were rendering the name and age fields of a model:
<form method="post">
{{ formset.management_form }}
{% for form in formset %}
{{ form.id }}
<ul>
<li>{{ form.name }}</li>
<li>{{ form.age }}</li>
</ul>
{% endfor %}
</form>
Notice how we need to explicitly render {{ form.id }}. This ensures that
the model formset, in the POST case, will work correctly. (This example
assumes a primary key named id. If you’ve explicitly defined your own
primary key that isn’t called id, make sure it gets rendered.)
models.BaseInlineFormSet¶Inline formsets is a small abstraction layer on top of model formsets. These simplify the case of working with related objects via a foreign key. Suppose you have these two models:
from django.db import models
class Author(models.Model):
name = models.CharField(max_length=100)
class Book(models.Model):
author = models.ForeignKey(Author, on_delete=models.CASCADE)
title = models.CharField(max_length=100)
If you want to create a formset that allows you to edit books belonging to a particular author, you could do this:
>>> from django.forms import inlineformset_factory
>>> BookFormSet = inlineformset_factory(Author, Book, fields=('title',))
>>> author = Author.objects.get(name='Mike Royko')
>>> formset = BookFormSet(instance=author)
BookFormSet’s prefix is 'book_set'
(<model name>_set ). If Book’s ForeignKey to Author has a
related_name, that’s used instead.
Note
inlineformset_factory() uses
modelformset_factory() and marks
can_delete=True.
InlineFormSet¶When overriding methods on InlineFormSet, you should subclass
BaseInlineFormSet rather than
BaseModelFormSet.
For example, if you want to override clean():
from django.forms import BaseInlineFormSet
class CustomInlineFormSet(BaseInlineFormSet):
def clean(self):
super().clean()
# example custom validation across forms in the formset
for form in self.forms:
# your custom formset validation
...
See also Overriding clean() on a ModelFormSet.
Then when you create your inline formset, pass in the optional argument
formset:
>>> from django.forms import inlineformset_factory
>>> BookFormSet = inlineformset_factory(Author, Book, fields=('title',),
... formset=CustomInlineFormSet)
>>> author = Author.objects.get(name='Mike Royko')
>>> formset = BookFormSet(instance=author)
If your model contains more than one foreign key to the same model, you’ll
need to resolve the ambiguity manually using fk_name. For example, consider
the following model:
class Friendship(models.Model):
from_friend = models.ForeignKey(
Friend,
on_delete=models.CASCADE,
related_name='from_friends',
)
to_friend = models.ForeignKey(
Friend,
on_delete=models.CASCADE,
related_name='friends',
)
length_in_months = models.IntegerField()
To resolve this, you can use fk_name to
inlineformset_factory():
>>> FriendshipFormSet = inlineformset_factory(Friend, Friendship, fk_name='from_friend',
... fields=('to_friend', 'length_in_months'))
You may want to provide a view that allows a user to edit the related objects of a model. Here’s how you can do that:
def manage_books(request, author_id):
author = Author.objects.get(pk=author_id)
BookInlineFormSet = inlineformset_factory(Author, Book, fields=('title',))
if request.method == "POST":
formset = BookInlineFormSet(request.POST, request.FILES, instance=author)
if formset.is_valid():
formset.save()
# Do something. Should generally end with a redirect. For example:
return HttpResponseRedirect(author.get_absolute_url())
else:
formset = BookInlineFormSet(instance=author)
return render(request, 'manage_books.html', {'formset': formset})
Notice how we pass instance in both the POST and GET cases.
inlineformset_factory uses modelformset_factory and passes most
of its arguments to modelformset_factory. This means you can use
the widgets parameter in much the same way as passing it to
modelformset_factory. See Specifying widgets to use in the form with
widgets above.
Jul 28, 2023