Common Needs¶

This chapter collects solutions for requirements that will often crop up once you start using Deform for real world applications.

Complex data loading, changing widgets, or validating ¶

For complex loading of data, changing widgets, or validating beyond the basic declarative schema, you can use Colander's schema binding feature. See the chapter in the Colander's documentation Schema Binding.

Changing the Default Widget Associated With a Field ¶

Let's take another look at our familiar schema:

import colander

class Person(colander.MappingSchema):
    name = colander.SchemaNode(colander.String())
    age = colander.SchemaNode(colander.Integer(),
                              validator=colander.Range(0, 200))

class People(colander.SequenceSchema):
    person = Person()

class Schema(colander.MappingSchema):
    people = People()

schema = Schema()

This schema renders as a sequence of mapping objects. Each mapping has two leaf nodes in it: a string and an integer. If you play around with the demo at https://deformdemo.pylonsproject.org/sequence_of_mappings/ you will notice that, although we do not actually specify a particular kind of widget for each of these fields, a sensible default widget is used. This is true of each of the default types in Colander. Here is how they are mapped by default. In the following list, the schema type which is the header uses the widget underneath it by default.

Note

Not just any widget can be used with any schema type; the documentation for each widget usually indicates what type it can be used against successfully. If all existing widgets provided by Deform are insufficient, you can use a custom widget. See Writing Your Own Widget for more information about writing a custom widget.

If you are creating a schema that contains a type which is not in this list, or if you would like to use a different widget for a particular field, or you want to change the settings of the default widget associated with the type, you need to associate the field with the widget "by hand". There are a number of ways to do so, as outlined in the sections below.

As an argument to a `colander.SchemaNode` constructor¶

As of Deform 0.8, you may specify the widget as part of the schema:

import colander

from deform import Form
from deform.widget import TextAreaWidget

class Person(colander.MappingSchema):
    name = colander.SchemaNode(colander.String(),
                               widget=TextAreaWidget())
    age = colander.SchemaNode(colander.Integer(),
                              validator=colander.Range(0, 200))

class People(colander.SequenceSchema):
    person = Person()

class Schema(colander.MappingSchema):
    people = People()

schema = Schema()

myform = Form(schema, buttons=('submit',))

Note above that we passed a widget argument to the name schema node in the Person class above. When a schema containing a node with a widget argument to a schema node is rendered by Deform, the widget specified in the node constructor is used as the widget which should be associated with that node's form rendering. In this case, we will use a deform.widget.TextAreaWidget as the name widget.

Note

Widget associations done in a schema are always overridden by explicit widget assignments performed via deform.Field.__setitem__() and deform.Field.set_widgets().

Using dictionary access to change the widget ¶

After the deform.Form constructor is called with the schema, you can change the widget used for a particular field by using dictionary access to get to the field in question. A deform.Form is just another kind of deform.Field, so the method works for either kind of object. For example:

from deform import Form
from deform.widget import TextInputWidget

myform = Form(schema, buttons=('submit',))
myform['people']['person']['name'].widget = TextInputWidget(size=10)

This associates the String field named name in the rendered form with an explicitly created deform.widget.TextInputWidget by finding the name field via a series of __getitem__ calls through the field structure, then by assigning an explicit widget attribute to the name field.

You might want to do this in order to pass a size argument to the explicit widget creation, indicating that the size of the name input field should be 10em rather than the default.

Although in the example above, we associated the name field with the same type of widget as its default, we could have associated the name field with a completely different widget using the same pattern. For example:

from deform import Form
from deform.widget import TextAreaWidget

myform = Form(schema, buttons=('submit',))
myform['people']['person']['name'].widget = TextAreaWidget()

The above renders an HTML textarea input element for the name field instead of an input type=text field. This probably does not make much sense for a field called name (names are not usually multiline paragraphs), but it does let us demonstrate how different widgets can be used for the same field.

Using the `deform.Field.set_widgets()` method¶

Equivalently, you can also use the deform.Field.set_widgets() method to associate multiple widgets with multiple fields in a form. For example:

from deform import Form
from deform.widget import TextAreaWidget

myform = Form(schema, buttons=('submit',))
myform.set_widgets({'people.person.name':TextAreaWidget(),
                    'people.person.age':TextAreaWidget()})

Each key in the dictionary passed to deform.Field.set_widgets() is a "dotted name" which resolves to a single field element. Each value in the dictionary is a widget instance. See deform.Field.set_widgets() for more information about this method and dotted name resolution, including special cases which involve the "splat" (*) character and the empty string as a key name.

Using arbitrary form attributes ¶

HTML5 introduced many attributes to HTML forms, most of which appear in the HTML <input> element as a type attribute. For the full specification, see https://www.w3.org/TR/2017/REC-html52-20171214/sec-forms.html#sec-forms For implementations and demos, the Mozilla Developer Network is one useful resource.

Starting with Deform 2.0.7, all of the Deform widgets support arbitrary HTML5 form attributes. They also support any arbitrary attribute, such as readonly or disabled. This is useful, for example, when you want to use any of the following new HTML5 input types.

color
date
datetime
datetime-local
email
month
number
range
search
tel
time
url
week

You can also set placeholders, use multiple file uploads, and set some client-side validation requirements without JavaScript.

The following Python code will generate the subsequent HTML and rendered HTML5 number input.

from decimal import Decimal

total_employee_hours = colander.SchemaNode(
    colander.Decimal(),
    widget=widget.TextInputWidget(
        attributes={
            "type": "number",
            "inputmode": "decimal",
            "step": "0.01",
            "min": "0",
            "max": "99.99",
        }
    ),
    validator=colander.Range(min=0, max=Decimal("99.99")),
    default=30.00,
    missing=colander.drop,
)

<input
    name="total_employee_hours"
    value="30.00"
    id="total_employee_hours"
    class=" form-control "
    type="number"
    inputmode="decimal"
    step="0.01"
    min="0"
    max="99.99">

Total employee hours

New in version 2.0.7: Arbitrary form control attributes, providing support for HTML5 forms.

Using `readonly` in HTML form control attributes ¶

Note

Naming things is hard. In Deform an unfortunate naming decision was made for readonly when rendering a form without any form controls using a "readonly" template. Oops. Looking back, we ought to have named it viewonly, static, immutable, or readable to avoid confusion with the HTML attribute readonly.

The readonly HTML form control attribute makes the element not mutable, meaning the user cannot edit the control. When "readonly": "readonly" is one of the items in a dict passed into the attributes option when creating a widget, the rendered widget both prevents the user from changing the value, and if the form does not pass validation after submitted then the field value will be displayed.

readonly is supported by most form controls, but not all. Deform adds some logic to add read-only support for a few of those form controls, as described below.

CheckboxWidget and CheckboxChoiceWidget: Due to the nature of how checkbox values are processed, the readonly attribute has no effect. To achieve a read-only behavior, pass in attributes={"onclick": "return false;"}. This will render as an inline JavaScript onclick="return false;" for each checkbox item.
MoneyInputWidget: The provided value will be displayed in the input and be not editable.
RadioChoiceWidget: For the selected value it will render an attribute in the HTML as readonly="readonly", and for all other values as disabled="disabled".
SelectWidget: For selection of single options only, the selected value will render an attribute in the HTML as readonly="readonly", and for all other values as disabled="disabled". Multiple selections, set by the multiple=True option, do not support the readonly attribute on the <select> element. For multiple selections, use the SelectizeWidget.
SelectizeWidget: For both single and multiple selections, the selected value or values will be rendered as selected, and the others will not be selectable. Selectize uses JavaScript to "lock" the form control.
TextAreaWidget: The provided value will be displayed in the input and be not editable.
TextInputWidget: The provided value will be displayed in the input and be not editable.

Warning

Regardless of using readonly, never trust user input or client-side only validation, and validate submitted data on the server side to ensure that values are not altered.

New in version 2.0.15: Enhanced readonly form control attribute.

Using Selectize Widget ¶

The Selectize widget is based on the jQuery plugin selectize.js.

Configuration options of the Selectize widget can be passed in as a dict to the keyword argument selectize_options. These options are rendered as inline JavaScript in the HTML widget. See the available configuration options at the selectize.js project.

By default, Deform treats any options with a "" value as normal by virtue of setting allowEmptyOption to True. This will render in HTML as <option value="">- Select -</option>. You can override this default value as follows.

widget=deform.widget.SelectizeWidget(
    values=choices,
    selectize_options={
        "allowEmptyOption": False,
    },
)

Using the above pattern, you can configure the Selectize widget for all of its configuration options.

Try a basic demonstration of the Selectize widget. Additional options are also demonstrated.

New in version 2.0.15.

Using Date, DateTime, and Time Inputs ¶

The deform.widget.DateInputWidget, deform.widget.DateTimeInputWidget, and deform.widget.TimeInputWidget inputs all use the jQuery plugin pickadate. This plugin is included with Deform in the directory static/pickadate.

Arbitrary options may be passed into the widget as a Python object, which will be automatically converted to a JSON object by the widget. These options are named date_options and time_options. This is useful to set a minimum or maximum date or time, and many other options. For the complete options, see date options or time options.

Use of these widgets is not a replacement for server-side validation of the field. It is purely a UI affordance. If the data must be checked at input time, a separate validator should be attached to the related schema node.

Using Text Input Masks ¶

The deform.widget.TextInputWidget and deform.widget.CheckedInputWidget widgets allow for the use of a fixed-length text input mask. Use of a text input mask causes placeholder text to be placed in the text field input, and restricts the type and length of the characters input into the text field.

For example:

form['ssn'].widget = TextInputWidget(mask='999-99-9999')

When using a text input mask:

a represents an alpha character (A-Z,a-z).
9 represents a numeric character (0-9).
* represents an alphanumeric character (A-Z,a-z,0-9).

All other characters in the mask will be considered mask literals.

By default the placeholder text for non-literal characters in the field will be _ (the underscore character). To change this for a given input field, use the mask_placeholder argument to the TextInputWidget:

form['date'].widget = TextInputWidget(mask='99/99/9999',
    mask_placeholder="-")

Example masks:

Date

99/99/9999

North American Phone Number

999-9999

United States Social Security Number

999-99-9999

When this option is used, the jquery.maskedinput library must be loaded into the page serving the form for the mask argument to have any effect. A copy of this library is available in the static/scripts directory of the deform package itself.

See https://deformdemo.pylonsproject.org/text_input_masks/ for a working example.

Use of a text input mask is not a replacement for server-side validation of the field. It is purely a UI affordance. If the data must be checked at input time, a separate validator should be attached to the related schema node.

Using the AutocompleteInputWidget ¶

The deform.widget.AutocompleteInputWidget widget allows for client side autocompletion from provided choices in a text input field. To use this you MUST ensure that jQuery and the jQuery UI plugin are available to the page where the deform.widget.AutocompleteInputWidget widget is rendered.

For convenience a version of the jQuery UI (which includes the autocomplete sublibrary) is included in the deform static directory. Additionally, the jQuery UI styles for the selection box are also included in the deform static directory. See Serving up the Rendered Form and The (High-Level) deform.Field.get_widget_resources() Method for more information about using the included libraries for your application.

A very simple example of using deform.widget.AutocompleteInputWidget follows:

form['frozznobs'].widget = AutocompleteInputWidget(
                             values=['spam', 'eggs', 'bar', 'baz'])

Instead of a list of values, a URL can be provided to values:

form['frobsnozz'].widget = AutocompleteInputWidget(
                             values='http://example.com/someapi')

In the above case, a call to the URL should provide results in a JSON-compatible format or JSONP-compatible response if on a different host than the application. Something like either of these structures in JSON are suitable.

// Items are used as both value and label
['item-one', 'item-two', 'item-three']

// Separate values and labels
[
    {'value': 'item-one', 'label': 'Item One'},
    {'value': 'item-two', 'label': 'Item Two'},
    {'value': 'item-three', 'label': 'Item Three'}
]

The autocomplete plugin will add a query string to the request URL with the variable term which contains the user's input at that moment. The server may use this to filter the returned results.

For more information, see https://api.jqueryui.com/autocomplete/#option-source — specifically, the section concerning the String type for the source option.

Some options for the jquery.autocomplete plugin are mapped and can be passed to the widget. See deform.widget.AutocompleteInputWidget for details regarding the available options. Passing options looks like:

form['nobsfrozz'].widget = AutocompleteInputWidget(
                            values=['spam, 'eggs', 'bar', 'baz'],
                            min_length=1)

See https://deformdemo.pylonsproject.org/autocomplete_input/ and https://deformdemo.pylonsproject.org/autocomplete_remote_input/ for working examples. A working example of a remote URL providing completion data can be found at https://deformdemo.pylonsproject.org/autocomplete_input_values/.

Use of deform.widget.AutocompleteInputWidget is not a replacement for server-side validation of the field. It is purely a UI affordance. If the data must be checked at input time, a separate validator should be attached to the related schema node.

Creating a New Schema Type ¶

Sometimes the default schema types offered by Colander may not be sufficient to model all the structures in your application.

If this happens, refer to the Colander documentation on Defining a New Type.

Common Needs¶

Customizing widget templates ¶

Complex data loading, changing widgets, or validating ¶

Changing the Default Widget Associated With a Field ¶

As an argument to a `colander.SchemaNode` constructor¶

Using dictionary access to change the widget ¶

Using the `deform.Field.set_widgets()` method¶

Using arbitrary form attributes ¶

Using `readonly` in HTML form control attributes ¶

Using Selectize Widget ¶

Using Date, DateTime, and Time Inputs ¶

Using Text Input Masks ¶

Using the AutocompleteInputWidget ¶

Creating a New Schema Type ¶

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Common Needs¶

As an argument to a colander.SchemaNode constructor¶

Using the deform.Field.set_widgets() method¶

As an argument to a `colander.SchemaNode` constructor¶

Using the `deform.Field.set_widgets()` method¶