""" 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