Using a form in a view

The standard pattern for processing a form in a view looks like this:

from django.shortcuts import render

from django.http import HttpResponseRedirect

def contact(request):

    if request.method == 'POST': # If the form has been submitted...

        form = ContactForm(request.POST) # A form bound to the POST data

        if form.is_valid(): # All validation rules pass

            # Process the data in form.cleaned_data

            # ...

            return HttpResponseRedirect('/thanks/') # Redirect after POST

    else:

        form = ContactForm() # An unbound form

    return render(request, 'contact.html', {

        'form': form,

    })

There are three possible code paths here:

The distinction between Bound and unbound forms is important:

• An unbound form has no data associated with it. When rendered to the user, it will be empty or will contain default values.
• A bound form has submitted data, and hence can be used to tell if that data is valid. If an invalid bound form is rendered, it can include inline error messages telling the user what data to correct.

★讲了form的两种状态：未绑定和绑定

Handling file uploads with a form

To see how to handle file uploads with your form, see Binding uploaded files to a form.

★用form上传文件，有特殊的规则

Processing the data from a form

Once is_valid() returns True, the successfully validated form data will be in the form.cleaned_data dictionary. This data will have been converted nicely into Python types for you.

★当 form 验证合格（is_valid() == True）时，用 form.cleaned_data 字典来取得数据。

In the above example, cc_myself will be a boolean value. Likewise, fields such as IntegerField andFloatField convert values to a Python int and float respectively.

Read-only fields are not available in form.cleaned_data (and setting a value in a custom clean() method won’t have any effect). These fields are displayed as text rather than as input elements, and thus are not posted back to the server.

Extending the earlier example, here’s how the form data could be processed:

if form.is_valid():

    subject = form.cleaned_data['subject']

    message = form.cleaned_data['message']

    sender = form.cleaned_data['sender']

    cc_myself = form.cleaned_data['cc_myself']

    recipients = ['info@example.com']

    if cc_myself:

        recipients.append(sender)

    from django.core.mail import send_mail

    send_mail(subject, message, sender, recipients)

    return HttpResponseRedirect('/thanks/') # Redirect after POST

Displaying a form using a template

Forms are designed to work with the Django template language. In the above example, we passed ourContactForm instance to the template using the context variable form. Here’s a simple example template:

<form action="/contact/" method="post">{% csrf_token %}

{{ form.as_p }}

<input type="submit" value="Submit" />

</form>

The form only outputs its own fields; it is up to you to provide the surrounding <form> tags and the submit button.

If your form includes uploaded files, be sure to include enctype="multipart/form-data" in the formelement. If you wish to write a generic template that will work whether or not the form has files, you can use the is_multipart() attribute on the form:

<form action="/contact/" method="post"

    {% if form.is_multipart %}enctype="multipart/form-data"{% endif %}>

form.as_p will output the form with each form field and accompanying label wrapped in a paragraph. Here’s the output for our example template:

<form action="/contact/" method="post">

<p><label for="id_subject">Subject:</label>

    <input id="id_subject" type="text" name="subject" maxlength="100" /></p>

<p><label for="id_message">Message:</label>

    <input type="text" name="message" id="id_message" /></p>

<p><label for="id_sender">Sender:</label>

    <input type="text" name="sender" id="id_sender" /></p>

<p><label for="id_cc_myself">Cc myself:</label>

    <input type="checkbox" name="cc_myself" id="id_cc_myself" /></p>

<input type="submit" value="Submit" />

</form>

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 customize the way in which labels and ids are generated.

★生成的form field有默认的ID为 id_<field-name> , 也可以定制ID的样式。

You can also use form.as_table to output table rows (you’ll need to provide your own <table> tags) andform.as_ul to output list items.

Customizing the form template

If the default generated HTML is not to your taste, you can completely customize the way a form is presented using the Django template language. Extending the above example:

<form action="/contact/" method="post">

    {{ form.non_field_errors }}

    <div class="fieldWrapper">

        {{ form.subject.errors }}

        <label for="id_subject">Email subject:</label>

        {{ form.subject }}

    </div>

    <div class="fieldWrapper">

        {{ form.message.errors }}

        <label for="id_message">Your message:</label>

        {{ form.message }}

    </div>

    <div class="fieldWrapper">

        {{ form.sender.errors }}

        <label for="id_sender">Your email address:</label>

        {{ form.sender }}

    </div>

    <div class="fieldWrapper">

        {{ form.cc_myself.errors }}

        <label for="id_cc_myself">CC yourself?</label>

        {{ form.cc_myself }}

    </div>

    <p><input type="submit" value="Send message" /></p>

</form>

Each named form-field can be output to the template using {{ form.name_of_field }}, which will produce the HTML needed to display the form widget. Using {{ form.name_of_field.errors }} displays a list of form errors, rendered as an unordered list. This might look like:

<ul class="errorlist">

    <li>Sender is required.</li>

</ul>

The list has a CSS class of errorlist to allow you to style its appearance. If you wish to further customize the display of errors you can do so by looping over them:

{% if form.subject.errors %}

    <ol>

    {% for error in form.subject.errors %}

        <li><strong>{{ error|escape }}</strong></li>

    {% endfor %}

    </ol>

{% endif %}

Looping over the form’s fields

If you’re using the same HTML for each of your form fields, you can reduce duplicate code by looping through each field in turn using a {% for %} loop:

<form action="/contact/" method="post">

    {% for field in form %}

        <div class="fieldWrapper">

            {{ field.errors }}

            {{ field.label_tag }}: {{ field }}

        </div>

    {% endfor %}

    <p><input type="submit" value="Send message" /></p>

</form>

Within this loop, {{ field }} is an instance of BoundField. BoundField also has the following attributes, which can be useful in your templates:

{{ field.label }}

The label of the field, e.g. Email address.

{{ field.label_tag }}

The field’s label wrapped in the appropriate HTML <label> tag, e.g.<label for="id_email">Email address</label>

{{ 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 some inline JavaScript and want to avoid hardcoding the field’s ID.

{{ field.value }}

The value of the field. e.g someone@example.com

{{ field.html_name }}

The name of the field that will be used in the input element’s name field. This takes the form prefix into account, if it has been set.

{{ field.help_text }}

Any help text that has been associated with the field.

{{ field.errors }}

Outputs a <ul class="errorlist"> containing any validation errors corresponding to this field. You can customize the presentation of the errors with a {% for error in field.errors %} loop. In this case, each object in the loop is a simple string containing the error message.

{{ field.is_hidden }}

This attribute is True if the form field is a hidden field and False otherwise. It’s not particularly useful as a template variable, but could be useful in conditional tests such as:

{% if field.is_hidden %}

   {# Do something special #}

{% endif %}

{{ field.field }}

The Field instance from the form class that this BoundField wraps. You can use it to access Fieldattributes , e.g. {{ char_field.field.max_length }}.

<form action="/contact/" method="post">

    {# Include the hidden fields #}

    {% for hidden in form.hidden_fields %}

    {{ hidden }}

    {% endfor %}

    {# Include the visible fields #}

    {% for field in form.visible_fields %}

        <div class="fieldWrapper">

            {{ field.errors }}

            {{ field.label_tag }}: {{ field }}

        </div>

    {% endfor %}

    <p><input type="submit" value="Send message" /></p>

</form>

Reusable form templates

If your site uses the same rendering logic for forms in multiple places, you can reduce duplication by saving the form’s loop in a standalone template and using the include tag to reuse it in other templates:

<form action="/contact/" method="post">

    {% include "form_snippet.html" %}

    <p><input type="submit" value="Send message" /></p>

</form>

# In form_snippet.html:

{% for field in form %}

    <div class="fieldWrapper">

        {{ field.errors }}

        {{ field.label_tag }}: {{ field }}

    </div>

{% endfor %}

If the form object passed to a template has a different name within the context, you can alias it using thewith argument of the include tag:

<form action="/comments/add/" method="post">

    {% include "form_snippet.html" with form=comment_form %}

    <p><input type="submit" value="Submit comment" /></p>

</form>

★在 include 语句中使用用 with 参数可以重命名。

If you find yourself doing this often, you might consider creating a custom inclusion tag.