TemplateResponse
and SimpleTemplateResponse
¶
Standard HttpResponse
objects are static structures.
They are provided with a block of pre-rendered content at time of
construction, and while that content can be modified, it isn’t in a form that
makes it easy to perform modifications.
However, it can sometimes be beneficial to allow decorators or middleware to modify a response after it has been constructed by the view. For example, you may want to change the template that is used, or put additional data into the context.
TemplateResponse provides a way to do just that. Unlike basic
HttpResponse
objects, TemplateResponse objects retain
the details of the template and context that was provided by the view to
compute the response. The final output of the response is not computed until
it is needed, later in the response process.
SimpleTemplateResponse
objects¶
-
class
SimpleTemplateResponse
¶
Attributes¶
-
SimpleTemplateResponse.
template_name
¶ The name of the template to be rendered. Accepts a backend-dependent template object (such as those returned by
get_template()
), the name of a template, or a list of template names.Example:
['foo.html', 'path/to/bar.html']
-
SimpleTemplateResponse.
context_data
¶ The context data to be used when rendering the template. It must be a
dict
.Example:
{'foo': 123}
-
SimpleTemplateResponse.
rendered_content
¶ The current rendered value of the response content, using the current template and context data.
-
SimpleTemplateResponse.
is_rendered
¶ A boolean indicating whether the response content has been rendered.
Methods¶
-
SimpleTemplateResponse.
__init__
(template, context=None, content_type=None, status=None, charset=None, using=None, headers=None)¶ Instantiates a
SimpleTemplateResponse
object with the given template, context, content type, HTTP status, and charset.template
- A backend-dependent template object (such as those returned by
get_template()
), the name of a template, or a list of template names. context
- A
dict
of values to add to the template context. By default, this is an empty dictionary. content_type
- The value included in the HTTP
Content-Type
header, including the MIME type specification and the character set encoding. Ifcontent_type
is specified, then its value is used. Otherwise,'text/html'
is used. status
- The HTTP status code for the response.
charset
- The charset in which the response will be encoded. If not given it will
be extracted from
content_type
, and if that is unsuccessful, theDEFAULT_CHARSET
setting will be used. using
- The
NAME
of a template engine to use for loading the template. headers
- A
dict
of HTTP headers to add to the response.
Changed in Django 3.2:The
headers
parameter was added.
-
SimpleTemplateResponse.
resolve_context
(context)¶ Preprocesses context data that will be used for rendering a template. Accepts a
dict
of context data. By default, returns the samedict
.Override this method in order to customize the context.
-
SimpleTemplateResponse.
resolve_template
(template)¶ Resolves the template instance to use for rendering. Accepts a backend-dependent template object (such as those returned by
get_template()
), the name of a template, or a list of template names.Returns the backend-dependent template object instance to be rendered.
Override this method in order to customize template loading.
-
SimpleTemplateResponse.
add_post_render_callback
()¶ Add a callback that will be invoked after rendering has taken place. This hook can be used to defer certain processing operations (such as caching) until after rendering has occurred.
If the
SimpleTemplateResponse
has already been rendered, the callback will be invoked immediately.When called, callbacks will be passed a single argument – the rendered
SimpleTemplateResponse
instance.If the callback returns a value that is not
None
, this will be used as the response instead of the original response object (and will be passed to the next post rendering callback etc.)
-
SimpleTemplateResponse.
render
()¶ Sets
response.content
to the result obtained bySimpleTemplateResponse.rendered_content
, runs all post-rendering callbacks, and returns the resulting response object.render()
will only have an effect the first time it is called. On subsequent calls, it will return the result obtained from the first call.
TemplateResponse
objects¶
-
class
TemplateResponse
¶ TemplateResponse
is a subclass ofSimpleTemplateResponse
that knows about the currentHttpRequest
.
Methods¶
-
TemplateResponse.
__init__
(request, template, context=None, content_type=None, status=None, charset=None, using=None, headers=None)¶ Instantiates a
TemplateResponse
object with the given request, template, context, content type, HTTP status, and charset.request
- An
HttpRequest
instance. template
- A backend-dependent template object (such as those returned by
get_template()
), the name of a template, or a list of template names. context
- A
dict
of values to add to the template context. By default, this is an empty dictionary. content_type
- The value included in the HTTP
Content-Type
header, including the MIME type specification and the character set encoding. Ifcontent_type
is specified, then its value is used. Otherwise,'text/html'
is used. status
- The HTTP status code for the response.
charset
- The charset in which the response will be encoded. If not given it will
be extracted from
content_type
, and if that is unsuccessful, theDEFAULT_CHARSET
setting will be used. using
- The
NAME
of a template engine to use for loading the template. headers
- A
dict
of HTTP headers to add to the response.
Changed in Django 3.2:The
headers
parameter was added.
The rendering process¶
Before a TemplateResponse
instance can be
returned to the client, it must be rendered. The rendering process takes the
intermediate representation of template and context, and turns it into the
final byte stream that can be served to the client.
There are three circumstances under which a TemplateResponse
will be
rendered:
- When the
TemplateResponse
instance is explicitly rendered, using theSimpleTemplateResponse.render()
method. - When the content of the response is explicitly set by assigning
response.content
. - After passing through template response middleware, but before passing through response middleware.
A TemplateResponse
can only be rendered once. The first call to
SimpleTemplateResponse.render()
sets the content of the response;
subsequent rendering calls do not change the response content.
However, when response.content
is explicitly assigned, the
change is always applied. If you want to force the content to be
re-rendered, you can re-evaluate the rendered content, and assign
the content of the response manually:
# Set up a rendered TemplateResponse
>>> from django.template.response import TemplateResponse
>>> t = TemplateResponse(request, 'original.html', {})
>>> t.render()
>>> print(t.content)
Original content
# Re-rendering doesn't change content
>>> t.template_name = 'new.html'
>>> t.render()
>>> print(t.content)
Original content
# Assigning content does change, no render() call required
>>> t.content = t.rendered_content
>>> print(t.content)
New content
Post-render callbacks¶
Some operations – such as caching – cannot be performed on an unrendered template. They must be performed on a fully complete and rendered response.
If you’re using middleware, you can do that. Middleware provides multiple opportunities to process a response on exit from a view. If you put behavior in the response middleware, it’s guaranteed to execute after template rendering has taken place.
However, if you’re using a decorator, the same opportunities do not exist. Any behavior defined in a decorator is handled immediately.
To compensate for this (and any other analogous use cases),
TemplateResponse
allows you to register callbacks that will
be invoked when rendering has completed. Using this callback, you can
defer critical processing until a point where you can guarantee that
rendered content will be available.
To define a post-render callback, define a function that takes a single argument – response – and register that function with the template response:
from django.template.response import TemplateResponse
def my_render_callback(response):
# Do content-sensitive processing
do_post_processing()
def my_view(request):
# Create a response
response = TemplateResponse(request, 'mytemplate.html', {})
# Register the callback
response.add_post_render_callback(my_render_callback)
# Return the response
return response
my_render_callback()
will be invoked after the mytemplate.html
has been rendered, and will be provided the fully rendered
TemplateResponse
instance as an argument.
If the template has already been rendered, the callback will be invoked immediately.
Using TemplateResponse
and SimpleTemplateResponse
¶
A TemplateResponse
object can be used anywhere that a normal
django.http.HttpResponse
can be used. It can also be used as an
alternative to calling render()
.
For example, the following view returns a TemplateResponse
with a
template and a context containing a queryset:
from django.template.response import TemplateResponse
def blog_index(request):
return TemplateResponse(request, 'entry_list.html', {'entries': Entry.objects.all()})