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Fixed and enhanced new HTML form docs.

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Matt Deacalion Stevens 2014-06-25 17:23:04 +01:00 committed by Tim Graham
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docs/topics/forms/index.txt
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@ -11,12 +11,12 @@ Working with forms
the forms API, see :doc:`/ref/forms/api`, :doc:`/ref/forms/fields`, and
:doc:`/ref/forms/validation`.
Unless you're planning to build websites and applications that do nothing but
Unless you're planning to build Web sites and applications that do nothing but
publish content, and don't accept input from your visitors, you're going to
need to understand and use forms.
Django provides a range of tools and libraries to help you build forms to
accept input from site visitors, and process and respond to the input.
accept input from site visitors, and then process and respond to the input.
HTML forms
==========
@ -39,11 +39,11 @@ As well as its ``<input>`` elements, a form must specify two things:
* *how*: the HTTP method the data should be returned by
As an example, the standard Django login form contains several ``<input>``
elements: one of ``type="text"`` for the username, one of ``type="password"``
for the password, and one of one of ``type="submit"`` for the "Log in" button.
It also contains some hidden text fields that the user doesn't see, that Django
uses to determine what to do next.
As an example, the login form for the Django admin contains several
``<input>`` elements: one of ``type="text"`` for the username, one of
``type="password"`` for the password, and one of ``type="submit"`` for the
"Log in" button. It also contains some hidden text fields that the user
doesn't see, which Django uses to determine what to do next.
It also tells the browser that the form data should be sent to the URL
specified in the ``<form>``’s ``action`` attribute - ``/admin/`` - and that it
@ -51,7 +51,7 @@ should be sent using the HTTP mechanism specified by the ``method`` attribute -
``post``.
When the ``<input type="submit" value="Log in">`` element is triggered, the
data are returned to ``/admin/``.
data is returned to ``/admin/``.
``GET`` and ``POST``
--------------------
@ -59,11 +59,11 @@ data are returned to ``/admin/``.
``GET`` and ``POST`` are the only HTTP methods to use when dealing with forms.
Django's login form is returned using the ``POST`` method, in which the browser
bundles up the form data, encodes them for transmission, sends them back to
the server, and then receives its response.
bundles up the form data, encodes it for transmission, sends it back to the
server, and then receives its response.
``GET`` by contrast bundles the submitted data into a string, and uses this to
compose a URL. The URL contains the address where the data must be sent, as
``GET``, by contrast, bundles the submitted data into a string, and uses this
to compose a URL. The URL contains the address where the data must be sent, as
well as the data keys and values. You can see this in action if you do a search
in the Django documentation, which will produce a URL of the form
``https://docs.djangoproject.com/search/?q=forms&release=1``.
@ -75,9 +75,9 @@ a request that makes changes in the database - should use ``POST``. ``GET``
should be used only for requests that do not affect the state of the system.
``GET`` would also be unsuitable for a password form, because the password
would appear in the URL, and thus also in browser history and server logs,
would appear in the URL, and thus, also in browser history and server logs,
all in plain text. Neither would it be suitable for large quantities of data,
or for binary data, such as an image. A web application that uses ``GET``
or for binary data, such as an image. A Web application that uses ``GET``
requests for admin forms is a security risk: it can be easy for an attacker to
mimic a form's request to gain access to sensitive parts of the system.
``POST``, coupled with other protections like Django's :doc:`CSRF protection
@ -91,22 +91,22 @@ Django's role in forms
======================
Handling forms is a complex business. Consider Django's admin, where numerous
items of data of various different types may need to be prepared for display in
items of data of several different types may need to be prepared for display in
a form, rendered as HTML, edited using a convenient interface, returned to the
server, validated and cleaned up, and then saved or passed on for further
processing.
Django's form functionality can simplify and automate vast portions of this
work, and also do it more safely and securely than most programmers would be
able to do in code they wrote themselves.
work, and can also do it more securely than most programmers would be able to
do in code they wrote themselves.
Django handles three distinct parts of the work involved in forms.
Django handles three distinct parts of the work involved in forms:
* preparing and restructuring data ready for rendering
* creating HTML forms for the data
* receiving and processing submitted forms and data from the client
It's *possible* to write code that does all of this manually, but Django can
It is *possible* to write code that does all of this manually, but Django can
take care of it all for you.
Forms in Django
@ -115,7 +115,7 @@ Forms in Django
We've described HTML forms briefly, but an HTML ``<form>`` is just one part of
the machinery required.
In the context of a web application, 'form' might refer to that HTML
In the context of a Web application, 'form' might refer to that HTML
``<form>``, or to the Django :class:`Form` that produces it, or to the
structured data returned when it is submitted, or to the end-to-end working
collection of these parts.
@ -134,8 +134,9 @@ maps a model class's fields to HTML form ``<input>`` elements via a
:class:`Form`; this is what the Django admin is based upon.)
A form's fields are themselves classes; they manage form data and perform
validation when a form is submitted. A ``DateField`` and a ``FileField`` handle
very different kinds of data and have to do different things with them.
validation when a form is submitted. A :class:`DateField` and a
:class:`FileField` handle very different kinds of data and have to do
different things with it.
A form field is represented to a user in the browser as a HTML "widget" - a
piece of user interface machinery. Each field type has an appropriate default
@ -145,7 +146,7 @@ required.
Instantiating, processing, and rendering forms
----------------------------------------------
When rendering an object in Django we generally:
When rendering an object in Django, we generally:
1. get hold of it in the view (fetch it from the database, for example)
2. pass it to the template context
@ -154,13 +155,13 @@ When rendering an object in Django we generally:
Rendering a form in a template involves nearly the same work as rendering any
other kind of object, but there are some key differences.
In the case of a model instance that contained no data it would rarely if ever
In the case of a model instance that contained no data, it would rarely if ever
be useful to do anything with one in a template. On the other hand, it makes
perfect sense to render an unpopulated form - that's what we do when we want
the user to populate it.
So when we handle a model instance in a view we typically retrieve it from the
database; when we're dealing with a form we typically instantiate it in the
So when we handle a model instance in a view, we typically retrieve it from the
database. When we're dealing with a form we typically instantiate it in the
view.
When we instantiate a form, we can opt to leave it empty or pre-populate it, for
@ -171,17 +172,17 @@ example with:
* data received from a previous HTML form submission
The last of these cases is the most interesting, because it's what makes it
possible for users not just to read a website, but to send information back to
it too.
possible for users not just to read a Web site, but to send information back
to it too.
Building a form
===============
The work that needs to done
---------------------------
The work that needs to be done
------------------------------
Suppose you want to create a simple form on your website, to obtain the user's
name. You'd need something like this in your template:
Suppose you want to create a simple form on your Web site, in order to obtain
the user's name. You'd need something like this in your template:
.. code-block:: html+django
@ -199,11 +200,11 @@ variable, that will be used to pre-fill the ``your_name`` field.
You'll need a view that renders the template containing the HTML form, and
that can supply the ``current_name`` field as appropriate.
When the form is submitted, the ``POST`` request sent to the server will contain
the form data.
When the form is submitted, the ``POST`` request which is sent to the server
will contain the form data.
Now you'll also need a view corresponding to that ``/your-name/`` URL which will
find the appropriate key/value pairs in the request and process them.
find the appropriate key/value pairs in the request, and then process them.
This is a very simple form. In practice, a form might contain dozens or
hundreds of fields, many of which might need to be pre-populated, and we might
@ -212,7 +213,7 @@ concluding the operation.
We might require some validation to occur in the browser, even before the form
is submitted; we might want to use much more complex fields, that allow the
user to do things like pick dates from a calendar; and so on.
user to do things like pick dates from a calendar and so on.
At this point it's much easier to get Django to do most of this work for us.
@ -233,7 +234,7 @@ it in Django is this:
your_name = forms.CharField(label='Your name', max_length=100)
This defines a :class:`Form` class with a single field (``your_name``). We've
applied a human-friendly label to the field, that will appear in the
applied a human-friendly label to the field, which will appear in the
``<label>`` when it's rendered (although in this case, the :attr:`~Field.label`
we specified is actually the same one that would be generated automatically if
we had omitted it).
@ -241,9 +242,9 @@ we had omitted it).
The field's maximum allowable length is defined by
:attr:`~CharField.max_length`. This does two things. It puts a
``maxlength="100"`` on the HTML ``<input>`` (so the browser should prevent the
user entering more than that many characters in the first place). It also means
that when Django receives the form back from the browser, it will validate the
length of the data.
user from entering more than that number of characters in the first place). It
also means that when Django receives the form back from the browser, it will
validate the length of the data.
A :class:`Form` instance has an :meth:`~Form.is_valid()` method, which runs
validation routines for all its fields. When this method is called, if all
@ -267,8 +268,8 @@ We'll have to provide those ourselves in the template.
The view
^^^^^^^^
Form data sent back to a Django website are processed by a view, generally the
same view that published the form. This allows us to reuse some of the same
Form data sent back to a Django Web site is processed by a view, generally the
same view which published the form. This allows us to reuse some of the same
logic.
To handle the form we need to instantiate it in the view for the URL where we
@ -303,7 +304,7 @@ can expect to happen the first time we visit the URL.
If the form is submitted using a ``POST`` request, the view will once again
create a form instance and populate it with data from the request: ``form =
NameForm(request.POST)`` (this is called "binding data to the form" - it is now
NameForm(request.POST)`` This is called "binding data to the form" (it is now
a *bound* form).
We call the form's ``is_valid()`` method; if it's not ``True``, we go back to
@ -312,7 +313,7 @@ so the HTML form will be populated with the data previously submitted, where it
can be edited and corrected as required.
If ``is_valid()`` is ``True``, we'll now be able to find all the validated form
data in its ``cleaned_data`` attribute. We can use these data to update the
data in its ``cleaned_data`` attribute. We can use this data to update the
database or do other processing before sending an HTTP redirect to the browser
telling it where to go next.
@ -355,9 +356,9 @@ and know a little bit about some of the underlying machinery.
More about Django :class:`Form` classes
=======================================
All form classes are created as subclasses of ``django.forms.Form``, including
the :doc:`ModelForm </topics/forms/modelforms>` you encounter in Django's
admin.
All form classes are created as subclasses of :class:`django.forms.Form`,
including the :doc:`ModelForm </topics/forms/modelforms>`, which you encounter
in Django's admin.
.. admonition:: Models and Forms
@ -384,8 +385,8 @@ it or not.
More on fields
--------------
Consider a rather more useful form than our minimal example above, that
we could use to implement "contact me" functionality on a personal Web site:
Consider a more useful form than our minimal example above, which we could use
to implement "contact me" functionality on a personal Web site:
.. code-block:: python
@ -397,8 +398,8 @@ we could use to implement "contact me" functionality on a personal Web site:
sender = forms.EmailField()
cc_myself = forms.BooleanField(required=False)
Our earlier form used a single field, ``your_name``, a ``CharField``. In this
case, our form has four fields: ``subject``, ``message``, ``sender`` and
Our earlier form used a single field, ``your_name``, a :class:`CharField`. In
this case, our form has four fields: ``subject``, ``message``, ``sender`` and
``cc_myself``. :class:`CharField`, :class:`EmailField` and
:class:`BooleanField` are just three of the available field types; a full list
can be found in :doc:`/ref/forms/fields`.
@ -411,10 +412,10 @@ which in turn corresponds to an HTML form widget such as ``<input
type="text">``.
In most cases, the field will have a sensible default widget. For example, by
default, a ``CharField`` will have a :class:`TextInput` widget, that produces an
``<input type="text">`` in the HTML. If you needed ``<input type="textarea">``
instead, you'd specify the appropriate widget when defining your form field,
as we have done for the ``message`` field.
default, a :class:`CharField` will have a :class:`TextInput` widget, that
produces an ``<input type="text">`` in the HTML. If you needed
``<input type="textarea">`` instead, you'd specify the appropriate widget when
defining your form field, as we have done for the ``message`` field.
Field data
^^^^^^^^^^
@ -422,7 +423,7 @@ Field data
Whatever the data submitted with a form, once it has been successfully
validated by calling ``is_valid()`` (and ``is_valid()`` has returned ``True``),
the validated form data will be in the ``form.cleaned_data`` dictionary. This
data will have been converted nicely into Python types for you.
data will have been nicely converted into Python types for you.
.. note::
@ -504,9 +505,9 @@ Here's the output of ``{{ form.as_p }}`` for our ``ContactForm`` instance:
<input type="checkbox" name="cc_myself" id="id_cc_myself" /></p>
Note that each form field has an ID attribute set to ``id_<field-name>``, which
is referenced by the accompanying label tag. This is important for ensuring
forms are accessible to assistive technology such as screen reader software. You
can also :ref:`customize the way in which labels and ids are generated
is referenced by the accompanying label tag. This is important in ensuring that
forms are accessible to assistive technology such as screen reader software.
You can also :ref:`customize the way in which labels and ids are generated
<ref-forms-api-configuring-label>`.
See :ref:`ref-forms-api-outputting-html` for more on this.
@ -546,7 +547,7 @@ in a Django template, will be rendered appropriately. For example:
Rendering form error messages
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The price of this flexibility of course is more work. Until now we haven't had
Of course, the price of this flexibility is more work. Until now we haven't had
to worry about how to display form errors, because that's taken care of for us.
In this example we have had to make sure we take care of any errors for each
field and any errors for the form as a whole. Note ``{{ form.non_field_errors
@ -621,8 +622,8 @@ Useful attributes on ``{{ field }}`` include:
``{{ field.id_for_label }}``
The ID that will be used for this field (``id_email`` in the example
above). You may want to use this in lieu of ``label_tag`` if you are
constructing the label manually. It's also useful, for example, if you have
above). If you are constructing the label manually, you may want to use
this in lieu of ``label_tag``. It's also useful, for example, if you have
some inline JavaScript and want to avoid hardcoding the field's ID.
``{{ field.value }}``