"""
34. Generating HTML forms from models
Django provides shortcuts for creating Form objects from a model class and a
model instance.
The function django.newforms.form_for_model() takes a model class and returns
a Form that is tied to the model. This Form works just like any other Form,
with one additional method: create(). The create() method creates an instance
of the model and returns that newly created instance. It saves the instance to
the database if create(save=True), which is default. If you pass
create(save=False), then you'll get the object without saving it.
The function django.newforms.form_for_instance() takes a model instance and
returns a Form that is tied to the instance. This form works just like any
other Form, with one additional method: apply_changes(). The apply_changes()
method updates the model instance. It saves the changes to the database if
apply_changes(save=True), which is default. If you pass save=False, then you'll
get the object without saving it.
"""
from django.db import models
class Category(models.Model):
name = models.CharField(maxlength=20)
url = models.CharField('The URL', maxlength=40)
def __str__(self):
return self.name
class Writer(models.Model):
name = models.CharField(maxlength=50)
def __str__(self):
return self.name
class Article(models.Model):
headline = models.CharField(maxlength=50)
pub_date = models.DateField()
writer = models.ForeignKey(Writer)
categories = models.ManyToManyField(Category, blank=True)
def __str__(self):
return self.headline
__test__ = {'API_TESTS': """
>>> from django.newforms import form_for_model, form_for_instance, BaseForm
>>> import datetime
>>> Category.objects.all()
[]
>>> CategoryForm = form_for_model(Category)
>>> f = CategoryForm()
>>> print f
>>> print f.as_ul()
>>> print f['name']
>>> f = CategoryForm(auto_id=False)
>>> print f.as_ul()
Name:
The URL:
>>> f = CategoryForm({'name': 'Entertainment', 'url': 'entertainment'})
>>> f.is_valid()
True
>>> f.clean_data
{'url': u'entertainment', 'name': u'Entertainment'}
>>> obj = f.create()
>>> obj
>>> Category.objects.all()
[]
>>> f = CategoryForm({'name': "It's a test", 'url': 'test'})
>>> f.is_valid()
True
>>> f.clean_data
{'url': u'test', 'name': u"It's a test"}
>>> obj = f.create()
>>> obj
>>> Category.objects.all()
[, ]
If you call create() with save=False, then it will return an object that hasn't
yet been saved. In this case, it's up to you to save it.
>>> f = CategoryForm({'name': 'Third test', 'url': 'third'})
>>> f.is_valid()
True
>>> f.clean_data
{'url': u'third', 'name': u'Third test'}
>>> obj = f.create(save=False)
>>> obj
>>> Category.objects.all()
[, ]
>>> obj.save()
>>> Category.objects.all()
[, , ]
If you call create() with invalid data, you'll get a ValueError.
>>> f = CategoryForm({'name': '', 'url': 'foo'})
>>> f.errors
{'name': [u'This field is required.']}
>>> f.clean_data
Traceback (most recent call last):
...
AttributeError: 'CategoryForm' object has no attribute 'clean_data'
>>> f.create()
Traceback (most recent call last):
...
ValueError: The Category could not be created because the data didn't validate.
>>> f = CategoryForm({'name': '', 'url': 'foo'})
>>> f.create()
Traceback (most recent call last):
...
ValueError: The Category could not be created because the data didn't validate.
Create a couple of Writers.
>>> w = Writer(name='Mike Royko')
>>> w.save()
>>> w = Writer(name='Bob Woodward')
>>> w.save()
ManyToManyFields are represented by a MultipleChoiceField, and ForeignKeys are
represented by a ChoiceField.
>>> ArticleForm = form_for_model(Article)
>>> f = ArticleForm(auto_id=False)
>>> print f
Headline:
Pub date:
Writer:
Categories:
You can pass a custom Form class to form_for_model. Make sure it's a
subclass of BaseForm, not Form.
>>> class CustomForm(BaseForm):
... def say_hello(self):
... print 'hello'
>>> CategoryForm = form_for_model(Category, form=CustomForm)
>>> f = CategoryForm()
>>> f.say_hello()
hello
Use form_for_instance to create a Form from a model instance. There are two
differences between this Form and one created via form_for_model. First, the
object's current values are inserted as 'initial' data in each Field. Second,
the Form gets an apply_changes() method instead of a create() method.
>>> w = Writer.objects.get(name='Mike Royko')
>>> RoykoForm = form_for_instance(w)
>>> f = RoykoForm(auto_id=False)
>>> print f