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 let you create a Form class from a Django model.
For example:
>>> from django.forms import ModelForm
# Create the form class.
>>> class ArticleForm(ModelForm):
... class Meta:
... model = Article
# 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. 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:
| Model field | Form field |
|---|---|
| AutoField | Not represented in the form |
| BigIntegerField | IntegerField with min_value set to -9223372036854775808 and max_value set to 9223372036854775807. |
| BooleanField | BooleanField |
| CharField | CharField with max_length set to the model field’s max_length |
| CommaSeparatedIntegerField | CharField |
| DateField | DateField |
| DateTimeField | DateTimeField |
| DecimalField | DecimalField |
| EmailField | EmailField |
| FileField | FileField |
| FilePathField | CharField |
| FloatField | FloatField |
| ForeignKey | ModelChoiceField (see below) |
| ImageField | ImageField |
| IntegerField | IntegerField |
| IPAddressField | IPAddressField |
| GenericIPAddressField | GenericIPAddressField |
| ManyToManyField | ModelMultipleChoiceField (see below) |
| NullBooleanField | CharField |
| PositiveIntegerField | IntegerField |
| PositiveSmallIntegerField | IntegerField |
| SlugField | SlugField |
| SmallIntegerField | IntegerField |
| TextField | CharField with widget=forms.Textarea |
| TimeField | TimeField |
| URLField | URLField |
As you might expect, the ForeignKey and ManyToManyField model field types are special cases:
In addition, each generated form field has attributes set as follows:
Finally, note that you can override the form field used for a given model field. See Overriding the default field types or widgets 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 __unicode__(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
class BookForm(ModelForm):
class Meta:
model = Book
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())
The first time you call is_valid() or access the errors attribute of a ModelForm triggers form validation as well as model validation. This has the side-effect of cleaning the model you pass to the ModelForm constructor. For instance, calling is_valid() on your form will convert any date fields on your model to actual date objects. If form validation fails, only some of the updates may be applied. For this reason, you’ll probably want to avoid reusing the model instance passed to the form, especially if validation fails.
Every form produced by 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:
# 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.
>>> a = Article.objects.get(pk=1)
>>> f = ArticleForm(instance=a)
>>> 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.
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 simple 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.
In some cases, you may not want all the model fields to appear on the generated form. There are three ways of telling ModelForm to use only a subset of the model fields:
For example, if you want a form for the Author model (defined above) that includes only the name and birth_date fields, you would specify fields or exclude like this:
class PartialAuthorForm(ModelForm):
class Meta:
model = Author
fields = ('name', 'birth_date')
class PartialAuthorForm(ModelForm):
class Meta:
model = Author
exclude = ('title',)
Since the Author model has only 3 fields, ‘name’, ‘title’, and ‘birth_date’, the forms above will contain exactly the same fields.
Note
If you specify fields or exclude when creating a form with ModelForm, then the fields that are not in the resulting form 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 type and widget for a given model field.
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 a 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
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).
If you want to further customize a field – including its type, label, etc. – you can do this by declaratively specifying fields like you would in a regular Form. Declared fields will override the default ones generated by using the model attribute.
For example, if you wanted to use MyDateFormField for the pub_date field, you could do the following:
class ArticleForm(ModelForm):
pub_date = MyDateFormField()
class Meta:
model = Article
If you want to override a field’s default label, then specify the label parameter when declaring the form field:
>>> class ArticleForm(ModelForm):
... pub_date = DateField(label='Publication date')
...
... class Meta:
... model = Article
Note
If you explicitly instantiate a form field like this, Django assumes that you want to completely define its behavior; therefore, default attributes (such as max_length or required) are not drawn 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
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, a ModelForm will render fields in the same order that they are defined on the model, with ManyToManyField instances appearing last. If you want to change the order in which fields are rendered, you can use the fields attribute on the Meta class.
The fields attribute defines the subset of model fields that will be rendered, and the order in which they will be rendered. For example given this model:
class Book(models.Model):
author = models.ForeignKey(Author)
title = models.CharField(max_length=100)
the author field would be rendered first. If we wanted the title field to be rendered first, we could specify the following ModelForm:
>>> class BookForm(ModelForm):
... class Meta:
... model = Book
... fields = ('title', 'author')
You can override the clean() method on a model form to provide additional validation in the same way you can on a normal form.
In this regard, model forms have two specific characteristics when compared to forms:
By default the clean() method validates the uniqueness of fields that are marked as unique, unique_together or unique_for_date|month|year on the model. Therefore, if you would like to override the clean() method and maintain the default validation, you must call the parent class’s clean() method.
Also, a model form instance bound to a model object will contain a self.instance attribute that gives model form methods access to that specific model instance.
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.excludes 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.
Chances are these notes won’t affect you unless you’re trying to do something tricky with subclassing.
As part of its 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. Also, your 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.
Like regular formsets, Django provides a couple of enhanced formset classes that make it easy to work with Django models. Let’s reuse the Author model from above:
>>> from django.forms.models import modelformset_factory
>>> AuthorFormSet = modelformset_factory(Author)
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-MAX_NUM_FORMS" 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="selected">---------</option>
<option value="MR">Mr.</option>
<option value="MRS">Mrs.</option>
<option value="MS">Ms.</option>
</select></td></tr>
<tr><th><label for="id_form-0-birth_date">Birth date:</label></th><td><input type="text" name="form-0-birth_date" id="id_form-0-birth_date" /><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 just an extension of a basic formset that knows how to interact with a particular model.
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.models import BaseModelFormSet
class BaseAuthorFormSet(BaseModelFormSet):
def __init__(self, *args, **kwargs):
super(BaseAuthorFormSet, self).__init__(*args, **kwargs)
self.queryset = Author.objects.filter(name__startswith='O')
Then, pass your BaseAuthorFormSet class to the factory function:
>>> AuthorFormSet = modelformset_factory(Author, 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, a model formset uses all fields in the model that are not marked with editable=False. However, this can be overridden at the formset level:
>>> 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',))
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 bound to an existing object instance.
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 Using a subset of fields on the form.
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.
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')
[<Author: Charles Baudelaire>, <Author: Paul Verlaine>, <Author: Walt Whitman>]
>>> AuthorFormSet = modelformset_factory(Author, max_num=1)
>>> formset = AuthorFormSet(queryset=Author.objects.order_by('name'))
>>> [x.name for x in formset.get_queryset()]
[u'Charles Baudelaire', u'Paul Verlaine', u'Walt Whitman']
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, 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 no limit on the number of forms displayed.
Model formsets are very similar to formsets. Let’s say we want to present a formset to edit Author model instances:
def manage_authors(request):
AuthorFormSet = modelformset_factory(Author)
if request.method == 'POST':
formset = AuthorFormSet(request.POST, request.FILES)
if formset.is_valid():
formset.save()
# do something.
else:
formset = AuthorFormSet()
return render_to_response("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.)
Just like with ModelForms, by default the clean() method of a model_formset 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 model_formset and maintain this validation, you must call the parent class’s clean method:
class MyModelFormSet(BaseModelFormSet):
def clean(self):
super(MyModelFormSet, self).clean()
# example custom validation across forms in the formset:
for form in self.forms:
# your custom formset validation
As stated earlier, you can override the default queryset used by the model formset:
def manage_authors(request):
AuthorFormSet = modelformset_factory(Author)
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_to_response("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" action="">
{{ formset }}
</form>
Second, you can manually render the formset, but let the form deal with itself:
<form method="post" action="">
{{ 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" action="">
{{ 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" action="">
{{ 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.)
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:
class Author(models.Model):
name = models.CharField(max_length=100)
class Book(models.Model):
author = models.ForeignKey(Author)
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.models import inlineformset_factory
>>> BookFormSet = inlineformset_factory(Author, Book)
>>> author = Author.objects.get(name=u'Mike Royko')
>>> formset = BookFormSet(instance=author)
Note
inlineformset_factory uses modelformset_factory and marks can_delete=True.
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)
to_friend = models.ForeignKey(Friend)
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")
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)
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_to_response("manage_books.html", {
"formset": formset,
})
Notice how we pass instance in both the POST and GET cases.
Dec 23, 2012