"""
This module collects helper functions and classes that "span" multiple levels
of MVC. In other words, these functions/classes introduce controlled coupling
for convenience's sake.
"""
from django.http import (
Http404,
HttpResponse,
HttpResponsePermanentRedirect,
HttpResponseRedirect,
)
from django.template import loader
from django.urls import NoReverseMatch, reverse
from django.utils.functional import Promise
def render(
request, template_name, context=None, content_type=None, status=None, using=None
):
"""
Return an HttpResponse whose content is filled with the result of calling
django.template.loader.render_to_string() with the passed arguments.
"""
content = loader.render_to_string(template_name, context, request, using=using)
return HttpResponse(content, content_type, status)
def redirect(to, *args, permanent=False, **kwargs):
"""
Return an HttpResponseRedirect to the appropriate URL for the arguments
passed.
The arguments could be:
* A model: the model's `get_absolute_url()` function will be called.
* A view name, possibly with arguments: `urls.reverse()` will be used
to reverse-resolve the name.
* A URL, which will be used as-is for the redirect location.
Issues a temporary redirect by default; pass permanent=True to issue a
permanent redirect.
"""
redirect_class = (
HttpResponsePermanentRedirect if permanent else HttpResponseRedirect
)
return redirect_class(resolve_url(to, *args, **kwargs))
def _get_queryset(klass):
"""
Return a QuerySet or a Manager.
Duck typing in action: any class with a `get()` method (for
get_object_or_404) or a `filter()` method (for get_list_or_404) might do
the job.
"""
# If it is a model class or anything else with ._default_manager
if hasattr(klass, "_default_manager"):
return klass._default_manager.all()
return klass
def get_object_or_404(klass, *args, **kwargs):
"""
Use get() to return an object, or raise an Http404 exception if the object
does not exist.
klass may be a Model, Manager, or QuerySet object. All other passed
arguments and keyword arguments are used in the get() query.
Like with QuerySet.get(), MultipleObjectsReturned is raised if more than
one object is found.
"""
queryset = _get_queryset(klass)
if not hasattr(queryset, "get"):
klass__name = (
klass.__name__ if isinstance(klass, type) else klass.__class__.__name__
)
raise ValueError(
"First argument to get_object_or_404() must be a Model, Manager, "
"or QuerySet, not '%s'." % klass__name
)
try:
return queryset.get(*args, **kwargs)
except queryset.model.DoesNotExist:
raise Http404(
"No %s matches the given query." % queryset.model._meta.object_name
)
def get_list_or_404(klass, *args, **kwargs):
"""
Use filter() to return a list of objects, or raise an Http404 exception if
the list is empty.
klass may be a Model, Manager, or QuerySet object. All other passed
arguments and keyword arguments are used in the filter() query.
"""
queryset = _get_queryset(klass)
if not hasattr(queryset, "filter"):
klass__name = (
klass.__name__ if isinstance(klass, type) else klass.__class__.__name__
)
raise ValueError(
"First argument to get_list_or_404() must be a Model, Manager, or "
"QuerySet, not '%s'." % klass__name
)
obj_list = list(queryset.filter(*args, **kwargs))
if not obj_list:
raise Http404(
"No %s matches the given query." % queryset.model._meta.object_name
)
return obj_list
def resolve_url(to, *args, **kwargs):
"""
Return a URL appropriate for the arguments passed.
The arguments could be:
* A model: the model's `get_absolute_url()` function will be called.
* A view name, possibly with arguments: `urls.reverse()` will be used
to reverse-resolve the name.
* A URL, which will be returned as-is.
"""
# If it's a model, use get_absolute_url()
if hasattr(to, "get_absolute_url"):
return to.get_absolute_url()
if isinstance(to, Promise):
# Expand the lazy instance, as it can cause issues when it is passed
# further to some Python functions like urlparse.
to = str(to)
# Handle relative URLs
if isinstance(to, str) and to.startswith(("./", "../")):
return to
# Next try a reverse URL resolution.
try:
return reverse(to, args=args, kwargs=kwargs)
except NoReverseMatch:
# If this is a callable, re-raise.
if callable(to):
raise
# If this doesn't "feel" like a URL, re-raise.
if "/" not in to and "." not in to:
raise
# Finally, fall back and assume it's a URL
return to