I am currently defining regular expressions in order to capture parameters in a URL, as described in the tutorial. How do I access parameters from the URL as part the HttpRequest object?
My HttpRequest.GET currently returns an empty QueryDict object.
I'd like to learn how to do this without a library, so I can get to know Django better.
When a URL is like domain/search/?q=haha, you would use request.GET.get('q', '').
q is the parameter you want, and '' is the default value if q isn't found.
However, if you are instead just configuring your URLconf**, then your captures from the regex are passed to the function as arguments (or named arguments).
Such as:
(r'^user/(?P<username>\w{0,50})/$', views.profile_page,),
Then in your views.py you would have
def profile_page(request, username):
# Rest of the method
To clarify camflan's explanation, let's suppose you have
the rule url(regex=r'^user/(?P<username>\w{1,50})/$', view='views.profile_page')
an incoming request for http://domain/user/thaiyoshi/?message=Hi
The URL dispatcher rule will catch parts of the URL path (here "user/thaiyoshi/") and pass them to the view function along with the request object.
The query string (here message=Hi) is parsed and parameters are stored as a QueryDict in request.GET. No further matching or processing for HTTP GET parameters is done.
This view function would use both parts extracted from the URL path and a query parameter:
def profile_page(request, username=None):
user = User.objects.get(username=username)
message = request.GET.get('message')
As a side note, you'll find the request method (in this case "GET", and for submitted forms usually "POST") in request.method. In some cases, it's useful to check that it matches what you're expecting.
Update: When deciding whether to use the URL path or the query parameters for passing information, the following may help:
use the URL path for uniquely identifying resources, e.g. /blog/post/15/ (not /blog/posts/?id=15)
use query parameters for changing the way the resource is displayed, e.g. /blog/post/15/?show_comments=1 or /blog/posts/2008/?sort_by=date&direction=desc
to make human-friendly URLs, avoid using ID numbers and use e.g. dates, categories, and/or slugs: /blog/post/2008/09/30/django-urls/
Using GET
request.GET["id"]
Using POST
request.POST["id"]
Someone would wonder how to set path in file urls.py, such as
domain/search/?q=CA
so that we could invoke query.
The fact is that it is not necessary to set such a route in file urls.py. You need to set just the route in urls.py:
urlpatterns = [
path('domain/search/', views.CityListView.as_view()),
]
And when you input http://servername:port/domain/search/?q=CA. The query part '?q=CA' will be automatically reserved in the hash table which you can reference though
request.GET.get('q', None).
Here is an example (file views.py)
class CityListView(generics.ListAPIView):
serializer_class = CityNameSerializer
def get_queryset(self):
if self.request.method == 'GET':
queryset = City.objects.all()
state_name = self.request.GET.get('q', None)
if state_name is not None:
queryset = queryset.filter(state__name=state_name)
return queryset
In addition, when you write query string in the URL:
http://servername:port/domain/search/?q=CA
Do not wrap query string in quotes. For example,
http://servername:port/domain/search/?q="CA"
def some_view(request, *args, **kwargs):
if kwargs.get('q', None):
# Do something here ..
For situations where you only have the request object you can use request.parser_context['kwargs']['your_param']
You have two common ways to do that in case your URL looks like that:
https://domain/method/?a=x&b=y
Version 1:
If a specific key is mandatory you can use:
key_a = request.GET['a']
This will return a value of a if the key exists and an exception if not.
Version 2:
If your keys are optional:
request.GET.get('a')
You can try that without any argument and this will not crash.
So you can wrap it with try: except: and return HttpResponseBadRequest() in example.
This is a simple way to make your code less complex, without using special exceptions handling.
I would like to share a tip that may save you some time.
If you plan to use something like this in your urls.py file:
url(r'^(?P<username>\w+)/$', views.profile_page,),
Which basically means www.example.com/<username>. Be sure to place it at the end of your URL entries, because otherwise, it is prone to cause conflicts with the URL entries that follow below, i.e. accessing one of them will give you the nice error: User matching query does not exist.
I've just experienced it myself; hope it helps!
These queries are currently done in two ways. If you want to access the query parameters (GET) you can query the following:
http://myserver:port/resource/?status=1
request.query_params.get('status', None) => 1
If you want to access the parameters passed by POST, you need to access this way:
request.data.get('role', None)
Accessing the dictionary (QueryDict) with 'get()', you can set a default value. In the cases above, if 'status' or 'role' are not informed, the values are None.
If you don't know the name of params and want to work with them all, you can use request.GET.keys() or dict(request.GET) functions
This is not exactly what you asked for, but this snippet is helpful for managing query_strings in templates.
If you only have access to the view object, then you can get the parameters defined in the URL path this way:
view.kwargs.get('url_param')
If you only have access to the request object, use the following:
request.resolver_match.kwargs.get('url_param')
Tested on Django 3.
views.py
from rest_framework.response import Response
def update_product(request, pk):
return Response({"pk":pk})
pk means primary_key.
urls.py
from products.views import update_product
from django.urls import path
urlpatterns = [
...,
path('update/products/<int:pk>', update_product)
]
You might as well check request.META dictionary to access many useful things like
PATH_INFO, QUERY_STRING
# for example
request.META['QUERY_STRING']
# or to avoid any exceptions provide a fallback
request.META.get('QUERY_STRING', False)
you said that it returns empty query dict
I think you need to tune your url to accept required or optional args or kwargs
Django got you all the power you need with regrex like:
url(r'^project_config/(?P<product>\w+)/$', views.foo),
more about this at django-optional-url-parameters
This is another alternate solution that can be implemented:
In the URL configuration:
urlpatterns = [path('runreport/<str:queryparams>', views.get)]
In the views:
list2 = queryparams.split("&")
url parameters may be captured by request.query_params
It seems more recommended to use request.query_params. For example,
When a URL is like domain/search/?q=haha, you would use request.query_params.get('q', None)
https://www.django-rest-framework.org/api-guide/requests/
"request.query_params is a more correctly named synonym for request.GET.
For clarity inside your code, we recommend using request.query_params instead of the Django's standard request.GET. Doing so will help keep your codebase more correct and obvious - any HTTP method type may include query parameters, not just GET requests."
I am using cache.memoize to memoize a function with Flask-Cache. How can I get the cache key which got set in the decorated function? How can I test that the function is cached during testing?
from flask import Flask
from flask.ext.cache import Cache
app = Flask(__name__)
cache = Cache(app, config={'CACHE_TYPE': 'simple'})
#cache.memoize(timeout=10)
def get_news(nid, lang=None):
return nid, lang
#app.route('/news/<str:nid>')
def news(news_id):
return 'News: ' + get_news(news_id)
When using memoize, the cache key is generated behind the scenes and should never need to be accessed manually. Flask-Cache is handling caching and retrieving the result of the function for you. But if you're interested in how Flask-Cache does it, you can look at the source. It is a hash of the function name, arguments, and a uuid.
You shouldn't need to test cache hits, because Flask-Cache is already tested. You should test your own code, not library code. But if you're interested in how Flask-Cache does it, you can look at the tests. It memoizes a function that returns the current time, then checks if the return is the same after sleeping.
If I have an object retrieved from a model, for example:
obj = Foo.objects.first()
I know that if I want to reference this object later and make sure that it has the current values from the database, I can call:
obj.refresh_from_db()
My question is, is there any advantage to using the refresh_from_db() method over simply doing?:
obj = Foo.objects.get(id=obj.id)
As far as I know, the result will be the same. refresh_from_db() seems more explicit, but in some cases it means an extra line of code. Lets say I update the value field for obj and later want to test that it has been updated to False. Compare:
obj = Foo.objects.first()
assert obj.value is True
# value of foo obj is updated somewhere to False and I want to test below
obj.refresh_from_db()
assert obj.value is False
with this:
obj = Foo.objects.first()
assert obj.value is True
# value of foo obj is updated somewhere to False and I want to test below
assert Foo.objects.get(id=obj.id).value is False
I am not interested in a discussion of which of the two is more pythonic. Rather, I am wondering if one method has a practical advantage over the other in terms of resources, performance, etc. I have read this bit of documentation, but I was not able to ascertain from that whether there is an advantage to using reload_db(). Thank you!
Django sources are usually relatively easy to follow. If we look at the refresh_from_db() implementation, at its core it is still using this same Foo.objects.get(id=obj.id) approach:
db_instance_qs = self.__class__._default_manager.using(db).filter(pk=self.pk)
...
db_instance_qs = db_instance_qs.only(*fields)
...
db_instance = db_instance_qs.get()
Only there are couple extra bells and whistles:
deferred fields are ignored
stale foreign key references are cleared (according to the comment explanation)
So for everyday usage it is safe to say that they are pretty much the same, use whatever you like.
Just to add to #serg's answer, there's a case where explicitly re-fetching from the db is helpful and refreshing from the db isn't so much useful.
This is the case when you're adding permissions to an object and checking them immediately afterwards, and you need to clear the cached permissions for the object so that your permission checks work as expected.
According to the permission caching section of the django documentation:
The ModelBackend caches permissions on the user object after the first time they need to be fetched for a permissions check. This is typically fine for the request-response cycle since permissions aren’t typically checked immediately after they are added (in the admin, for example). If you are adding permissions and checking them immediately afterward, in a test or view for example, the easiest solution is to re-fetch the user from the database...
For an example, consider this block of code inspired by the one in the documentation cited above:
from django.contrib.auth import get_user_model
from django.contrib.auth.models import Permission
from django.contrib.contenttypes.models import ContentType
from smoothies.models import Smoothie
def force_deblend(user, smoothie):
# Any permission check will cache the current set of permissions
if not user.has_perm('smoothies.deblend_smoothie'):
permission = Permission.objects.get(
codename='deblend_smoothie',
content_type=ContentType.objects.get_for_model(Smoothie)
)
user.user_permissions.add(permission)
# Subsequent permission checks hit the cached permission set
print(user.has_perm('smoothies.deblend_smoothie')) # False
# Re-fetch user (explicitly) from db to clear permissions cache
# Be aware that user.refresh_from_db() won't help here
user = get_user_model().objects.get(pk=user.pk)
# Permission cache is now repopulated from the database
print(user.has_perm('smoothies.deblend_smoothie')) # True
...
...
It seems there is a difference if you use cached properties.
See here:
p.roles[0]
<Role: 16888649>
p.refresh_from_db()
p.roles[0]
<Role: 16888649>
p = Person.objects.get(id=p.id)
p.roles[0]
<Role: 16888650>
Definition from models.py:
#cached_property
def roles(self):
return Role.objects.filter(employer__person=self).order_by("id")
I use redis cache backend and caching templates via django cache.
I create cache with template tag
{% cache 43200 object_detail object_detail.pk request.LANGUAGE_CODE %}
{% endcache %}
and in redis-cli I see smth like this
1) ":1:template.cache.object_detail.89484b14b36a8d5329426a3d944d2983"
My cache invalidation is a function that performed after saving object in UpdateView and takes this object:
def clear_cache_block(obj):
key = hashlib.md5()
obj_pk = obj.pk
key.update(str(obj))
cache.delete_pattern('*object_detail.'+str(key.hexdigest()))
but generated hash is not the same with hash in redis cache.
What should I use to clear cache only for object I update?
Function responsible for creating cache key for template tag is django.core.cache.utils.make_template_fragment_key. It takes as first argument your cache fragment name (in this case "object_detail" and as second argument all additional arguments passed to cache tag (in this case object_detail.pk and request.LANGUAGE_CODE). It will return complete key in format: template.cache.__YOUR_CACHE_FRAGMENT_NAME__.__HEX_DIGEST_OF_FRAGMENT_NAME_AND_PARAMETERS
If you want to know how that hex digest is computed, check source code
So your code should look like this:
from django.core.cache.utils import make_template_fragment_key
def clear_cache_block(obj, lang):
key = make_template_fragment_key('object_detail', (obj.id, lang))
cache.delete_pattern(key)
where key is language code for language that you're trying to clear cache. If you want to do it for all languages, you must do it in loop.
To reverse cache key you need all variables that you used to generate that key. cache template tag (here) uses function make_template_fragment_key to generate cache key.
So your cache invalidating function may look like:
from django.conf import settings
from django.core.cache.utils import make_template_fragment_key
def clear_cache_block(obj):
cache_key = make_template_fragment_key('object_detail',
(obj.id, settings.LANGUAGE_CODE))
cache.delete_pattern(cache_key)
Of course if you have more languages you need to iterate over language codes and invalidate cache for each language.
I want to have dict / list to which I can add values, just like models can be added to the admin register in django !
My attempt : (package -> __init__.py)
# Singleton object
# __init__.py (Package: pack)
class remember:
a = []
def add(data):
a.append[data]
def get():
return a
obj = remember()
# models1.py
import pack
pack.obj.add("data")
# models2.py
import pack
pack.obj.add("data2")
print pack.obj.get()
# We should get: ["data", "data2"]
# We get : ["data2"]
How to achieve the desired functionality ?
Some say that methods can do this if you don't need sub-classing, how to do this with methods ?
Update:
To be more clear :
Just like django admin register any one can import and register itself with admin, so that register is persisted between imports.
If it's a singleton you're after, have a look at this old blog post. It contains a link to a well documented implementation (here).
Don't. If you think you need a global you don't and you should reevaluate how you are approaching the problem because 99% of the time you're doing it wrong.
If you have a really good reason to do it perhaps thread_locals() will really solve the problem you're trying to solve. This allows you to set up thread level global data. Note: This is only slightly better than a true global and should in general be avoided, and it can cause you a lot of headaches.
If you're looking for a cross request "global" then you most likely want to look into storing values in memcached.