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Fixed #13997 - Added an example of constructing a MultiWidget and documented the value_from_datadict method.

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Tim Graham 2012-10-23 07:02:48 -04:00
parent ccb2b574e8
commit 04775b4598
1 changed files with 129 additions and 63 deletions
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192
docs/ref/forms/widgets.txt
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@ -214,38 +214,49 @@ foundation for custom widgets.
The 'value' given is not guaranteed to be valid input, therefore
subclass implementations should program defensively.
.. method:: value_from_datadict(self, data, files, name)
Given a dictionary of data and this widget's name, returns the value
of this widget. Returns ``None`` if a value wasn't provided.
.. class:: MultiWidget(widgets, attrs=None)
A widget that is composed of multiple widgets.
:class:`~django.forms.widgets.MultiWidget` works hand in hand with the
:class:`~django.forms.MultiValueField`.
.. method:: render(name, value, attrs=None)
:class:`MultiWidget` has one required argument:
Argument `value` is handled differently in this method from the
subclasses of :class:`~Widget`.
.. attribute:: MultiWidget.widgets
If `value` is a list, output of :meth:`~MultiWidget.render` will be a
concatenation of rendered child widgets. If `value` is not a list, it
will be first processed by the method :meth:`~MultiWidget.decompress()`
to create the list and then processed as above.
An iterable containing the widgets needed.
Unlike in the single value widgets, method :meth:`~MultiWidget.render`
need not be implemented in the subclasses.
And one required method:
.. method:: decompress(value)
Returns a list of "decompressed" values for the given value of the
multi-value field that makes use of the widget. The input value can be
assumed as valid, but not necessarily non-empty.
This method takes a single "compressed" value from the field and
returns a list of "decompressed" values. The input value can be
assumed valid, but not necessarily non-empty.
This method **must be implemented** by the subclass, and since the
value may be empty, the implementation must be defensive.
The rationale behind "decompression" is that it is necessary to "split"
the combined value of the form field into the values of the individual
field encapsulated within the multi-value field (e.g. when displaying
the partially or fully filled-out form).
the combined value of the form field into the values for each widget.
An example of this is how :class:`SplitDateTimeWidget` turns a
:class:`datetime` value into a list with date and time split into two
separate values::
class SplitDateTimeWidget(MultiWidget):
# ...
def decompress(self, value):
if value:
return [value.date(), value.time().replace(microsecond=0)]
return [None, None]
.. tip::
@ -254,6 +265,109 @@ foundation for custom widgets.
with the opposite responsibility - to combine cleaned values of
all member fields into one.
Other methods that may be useful to override include:
.. method:: render(name, value, attrs=None)
Argument ``value`` is handled differently in this method from the
subclasses of :class:`~Widget` because it has to figure out how to
split a single value for display in multiple widgets.
The ``value`` argument used when rendering can be one of two things:
* A ``list``.
* A single value (e.g., a string) that is the "compressed" representation
of a ``list`` of values.
If `value` is a list, output of :meth:`~MultiWidget.render` will be a
concatenation of rendered child widgets. If `value` is not a list, it
will be first processed by the method :meth:`~MultiWidget.decompress()`
to create the list and then processed as above.
In the second case -- i.e., if the value is *not* a list --
``render()`` will first decompress the value into a ``list`` before
rendering it. It does so by calling the ``decompress()`` method, which
:class:`MultiWidget`'s subclasses must implement (see above).
When ``render()`` executes its HTML rendering, each value in the list
is rendered with the corresponding widget -- the first value is
rendered in the first widget, the second value is rendered in the
second widget, etc.
Unlike in the single value widgets, method :meth:`~MultiWidget.render`
need not be implemented in the subclasses.
.. method:: format_output(rendered_widgets)
Given a list of rendered widgets (as strings), returns a Unicode string
representing the HTML for the whole lot.
This hook allows you to format the HTML design of the widgets any way
you'd like.
Here's an example widget which subclasses :class:`MultiWidget` to display
a date with the day, month, and year in different select boxes. This widget
is intended to be used with a :class:`~django.forms.DateField` rather than
a :class:`~django.forms.MultiValueField`, thus we have implemented
:meth:`~Widget.value_from_datadict`::
from datetime import date
from django.forms import widgets
class DateSelectorWidget(widgets.MultiWidget):
def __init__(self, attrs=None):
# create choices for days, months, years
# example below, the rest snipped for brevity.
years = [(year, year) for year in (2011, 2012, 2013)]
_widgets = (
widgets.Select(attrs=attrs, choices=days),
widgets.Select(attrs=attrs, choices=months),
widgets.Select(attrs=attrs, choices=years),
)
super(DateSelectorWidget, self).__init__(_widgets, attrs)
def decompress(self, value):
if value:
return [value.day, value.month, value.year]
return [None, None, None]
def format_output(self, rendered_widgets):
return u''.join(rendered_widgets)
def value_from_datadict(self, data, files, name):
datelist = [
widget.value_from_datadict(data, files, name + '_%s' % i)
for i, widget in enumerate(self.widgets)]
try:
D = date(day=int(datelist[0]), month=int(datelist[1]),
year=int(datelist[2]))
except ValueError:
return ''
else:
return str(D)
The constructor creates several :class:`Select` widgets in a tuple. The
``super`` class uses this tuple to setup the widget.
The :meth:`~MultiWidget.format_output` method is fairly vanilla here (in
fact, it's the same as what's been implemented as the default for
``MultiWidget``), but the idea is that you could add custom HTML between
the widgets should you wish.
The required method :meth:`~MultiWidget.decompress` breaks up a
``datetime.date`` value into the day, month, and year values corresponding
to each widget. Note how the method handles the case where ``value`` is
``None``.
The default implementation of :meth:`~Widget.value_from_datadict` returns
a list of values corresponding to each ``Widget``. This is appropriate
when using a ``MultiWidget`` with a :class:`~django.forms.MultiValueField`,
but since we want to use this widget with a :class:`~django.forms.DateField`
which takes a single value, we have overridden this method to combine the
data of all the subwidgets into a ``datetime.date``. The method extracts
data from the ``POST`` dictionary and constructs and validates the date.
If it is valid, we return the string, otherwise, we return an empty string
which will cause ``form.is_valid`` to return ``False``.
.. _built-in widgets:
@ -552,54 +666,6 @@ Composite widgets
:attr:`~Field.choices` attribute. If it does, it will override anything
you set here when the attribute is updated on the :class:`Field`.
``MultiWidget``
~~~~~~~~~~~~~~~
.. class:: MultiWidget
Wrapper around multiple other widgets. You'll probably want to use this
class with :class:`MultiValueField`.
Its ``render()`` method is different than other widgets', because it has to
figure out how to split a single value for display in multiple widgets.
Subclasses may implement ``format_output``, which takes the list of
rendered widgets and returns a string of HTML that formats them any way
you'd like.
The ``value`` argument used when rendering can be one of two things:
* A ``list``.
* A single value (e.g., a string) that is the "compressed" representation
of a ``list`` of values.
In the second case -- i.e., if the value is *not* a list -- ``render()``
will first decompress the value into a ``list`` before rendering it. It
does so by calling the ``decompress()`` method, which
:class:`MultiWidget`'s subclasses must implement. This method takes a
single "compressed" value and returns a ``list``. An example of this is how
:class:`SplitDateTimeWidget` turns a :class:`datetime` value into a list
with date and time split into two seperate values::
class SplitDateTimeWidget(MultiWidget):
# ...
def decompress(self, value):
if value:
return [value.date(), value.time().replace(microsecond=0)]
return [None, None]
When ``render()`` executes its HTML rendering, each value in the list is
rendered with the corresponding widget -- the first value is rendered in
the first widget, the second value is rendered in the second widget, etc.
:class:`MultiWidget` has one required argument:
.. attribute:: MultiWidget.widgets
An iterable containing the widgets needed.
``SplitDateTimeWidget``
~~~~~~~~~~~~~~~~~~~~~~~