I am using Django Rest and I need to decrease the value of an integer field by a certain quantity.
Right now I am first getting the value currently stored, then calculating the new value, and finally writing the new value back.
Is there any way to do this in a simpler way?
Tried to decide between commenting and writing long form. I think you are doing this best, if you are saying doing that server side vice like doing the calculation in javascript and then patching/ putting to update the model.
I'd probably do something like:
urls.py
...
url(r'^/descriptor/?p<model_link_pk>[\w\-]/subtract', viewsets.Subtractor.as_view(), name="subtract_thing_from_model"),
...
Then in the viewsets:
class Subtractor(APIView):
def post(self, request, format=None, model_link_pk=None):
model_link = ModelObject.objects.get(pk=model_link_pk)
model_link.integer_value -= request.data("subtract_by")
model_link.save()
return JsonResponse({"..."}) #or serializer
Let me know if this makes sense, or if a better way exists.
Related
I have a view which should accept an end point with a query parameter, as well as without a parameter.
http://localhost:8001/v1/subjects?owner_ids=62,144
and
http://localhost:8001/v1/subjects
Here's my view file...
class SubjectPagination(JsonApiPageNumberPagination):
"""
Required for frontend to retrieve full list.
"""
max_page_size = 5000
class SubjectViewSet(Subject.get_viewset()):
pagination_class = SubjectPagination
def get_queryset(self):
import pdb; pdb.set_trace()
queryset = Subject.objects.all()
if self.request.GET['owner_ids']:
owner_id_list = self.request.GET['owner_ids'].split(',')
owner_id_list_integer = []
for i in owner_id_list:
owner_id_list_integer.append(int(i))
return queryset.filter(organization__in=owner_id_list_integer)
else:
return queryset
SubjectUserRoleViewSet = Subject.get_by_user_role_viewset(
SubjectViewSet, GroupRoleMap, Role)
I am trying to figure out how to handle both the end points? Please advice what needs to be done at the view to handle a URI with or without query strings?
Here's the urls.py
router.register(r'subjects', views.SubjectViewSet)
First of all, is a good practice to send the parameters in url-form-encode, avoiding things like that, in this case for send a list you could send id as:
?owner_ids[]=62&owner_ids[]=144
the querydict its going to be like this :
<QueryDict: {'owner_ids[]': ['62', '144']}>
and you could process it easily, like this
self.request.GET.getlist('owner_ids[]', [])
remember to use the get and get list functions of the request method GET and POST, to avoid dict errors.
Second, split returns a list the for statement in owner list id is totally unnecessary, and the queryset statement __in accept array of strings, if you actually want to convert all the items to integers use list comprehensions. For example, to convert all the items in a list to integer, just have to use:
owner_ids = [int(i) for i in owner_ids ]
this is way more fast in python and way more pythonic, and also cool too see.
and last, all urls should finish in /, even django has a settings for that called append_slash
this is what i can tell about the ambiguous question you are asking, in the next times please write questions more precisely that help people help you.
So I'm new to Django...
First some background on how we do things now. We have a custom php system but I am constructing an improved inventory management system in django using only the admin interface. We store part numbers, and it is essential that we do not store duplicates. Part numbers can sometimes be entered with hypens, periods, spaces, etc. We need to be sure that duplicate parts are not added no matter what kind of formatting is entered. With our existing non-django system, we use a regex to strip anything from the string that is not a-zA-Z0-9. The actual entered part number is persisted, and the cleaned number is persisted to the db as well. Then when someone is adding a new part or even searching for a part, this cleaned version of the part number helps to avoid this ambiguity. We do the same for the manufacturer name.
My way of emulating this in django was to add the part_number_clean field along with the part_number field to the model. Then I overrode the save method to calculate the clean part number like so (manufacturer as well):
def save(self, *args, **kwargs):
self.manufacturer_clean = re.sub(r'[^a-zA-Z0-9]', '', self.manufacturer).lower()
self.part_number_clean = re.sub(r'[^a-zA-Z0-9]', '', self.part_number).lower()
super(CatalogProduct, self).save(*args, **kwargs)
The problem is, I need to unique on a combination of part number and manufacturer:
class Meta:
unique_together = ('part_number_clean ', 'manufacturer_clean ')
When I try to save a duplicate record, I get a database integrity violation. So it seems like django is evaluating the unique fields before the save function is called (which makes sense). I just need to know how or which method I should override to calculate these fields BEFORE any validation.
Additionally, I am interested in adding a third field to the unique_together mix that may or may not be filled out. If it is not filled it will just have an empty default value. I hope this will not cause any issues.
It would also be great if when the user tabbed-out of the manufacturer and part number fields, and both were not empty, some js would see if that product exists already, and offer the user the option to click a button and be whisked away to that record, before they waste their time filling out the rest of the data only to find that it already exists. I'm guessing this lies way outside the realm of the admin interface without serious hacking. Is there any way to somehow integrate this with the admin interface? Its working great for me up till now...
I figured it out. I'm posting the answer for anyone else that is curious. This was actually very simple in the end to implement in the model. All one needs to do is implement (override?) the clean() method of the model. In the method, I calculate and set my special fields, then be sure to call self.validate_unique() after. Works like a charm! No need to raise any exceptions, the form will display the error on top perfectly. Doing this in the save method will not work, as the exception cannot be thrown by your code or django at that point. Here is the code:
class CatalogProduct(models.Model):
manufacturer = models.CharField(max_length=100)
manufacturer_clean = models.CharField('Manufacturer',max_length=100,blank=True,editable=False)
part_number = models.CharField(max_length=100)
part_number_clean = models.CharField('Part number',max_length=100,blank=True,editable=False)
def clean(self):
# Calculate manufacturer_clean and part_number_clean
self.manufacturer_clean = re.sub(r'[^a-zA-Z0-9]', '', self.manufacturer).lower()
self.part_number_clean = re.sub(r'[^a-zA-Z0-9]', '', self.part_number).lower()
self.validate_unique()
The model is only responsible for describing data and how that data should be represented between your Python and database environment. It's because of this atomic role that models don't care about validation and what you've just went in there and introduced it.
You need a model form. It can clean the manufacturer and part number and also ensure that uniqueness constraints are satisfied as part of the validation process.
I'm trying to call a view directly from another (if this is at all possible). I have a view:
def product_add(request, order_id=None):
# Works. Handles a normal POST check and form submission and redirects
# to another page if the form is properly validated.
Then I have a 2nd view, that queries the DB for the product data and should call the first one.
def product_copy_from_history(request, order_id=None, product_id=None):
product = Product.objects.get(owner=request.user, pk=product_id)
# I need to somehow setup a form with the product data so that the first
# view thinks it gets a post request.
2nd_response = product_add(request, order_id)
return 2nd_response
Since the second one needs to add the product as the first view does it I was wondering if I could just call the first view from the second one.
What I'm aiming for is just passing through the request object to the second view and return the obtained response object in turn back to the client.
Any help greatly appreciated, critism as well if this is a bad way to do it. But then some pointers .. to avoid DRY-ing.
Thanx!
Gerard.
My god, what was I thinking. This would be the cleanest solution ofcourse:
def product_add_from_history(request, order_id=None, product_id=None):
""" Add existing product to current order
"""
order = get_object_or_404(Order, pk=order_id, owner=request.user)
product = Product.objects.get(owner=request.user, pk=product_id)
newproduct = Product(
owner=request.user,
order = order,
name = product.name,
amount = product.amount,
unit_price = product.unit_price,
)
newproduct.save()
return HttpResponseRedirect(reverse('order-detail', args=[order_id]) )
A view is a regular python method, you can of course call one from another giving you pass proper arguments and handle the result correctly (like 404...). Now if it is a good practice I don't know. I would myself to an utiliy method and call it from both views.
If you are fine with the overhead of calling your API through HTTP you can use urllib to post a request to your product_add request handler.
As far as I know this could add some troubles if you develop with the dev server that comes with django, as it only handles one request at a time and will block indefinitely (see trac, google groups).
We've got some clients sending a custom POST of a data blob to our django servers.
They do things in a rather funky way that I'd rather not get into - and we've since moved on from making that particular format the norm. To make further implementations of our upload protocol more streamlined, I was looking to roll a custom UploadHandler in django to make our data handling in the views a bit more streamlined.
So, moving forward, we want all code in the views to access our POSTs via the:
data = request.FILES['something']
So, for our new submissions, we're handling that dandily.
What I'd like to be able to do is get the upload handler we've made, affectionately called LegacyUploadHandler(), to populate the request.FILES dictionary with the right parts, so the code in our view can access the parts the same way.
So, my question:
How does a custom uploadhandler actually populate the request.FILES dictionary? The django documentation doesn't really give a descriptive example of doing that.
Our particular desire is that we have a singular blob of data coming in. We custom parse it and want it to appear as the request.FILES dictionary.
The current code as it stands right now does this:
def handle_raw_input(self, input_data, META, content_length, boundary, encoding=None):
files_dict = {}
files_dict = magic_parser(input_data.read())
#now what do I do?
I see examples of setting a files MultiValueDict in the http.MultiPartParser, but that seems to be outside the scope/control of where I am in my handlers.
Any ideas of how to actually do the return value? Or am I trying to populate the request.FILES object the completely wrong way?
From handle_raw_input you have to return a tuple of what will be POST and FILES on the requst. So in your case it's something like:
def handle_raw_input(self, input_data, META, content_length, boundary, encoding=None):
files_dict = magic_parser(input_data.read())
return QueryDict(), files_dict
The magic_parser should return a MultiValueDict of the form {'filename': fileobj}. A fileobj is an instance of some suitable django.core.files.File subclass (or may be that class itself).
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We just now started doing the A/B testing for our Django based project. Can I get some information on best practices or useful insights about this A/B testing.
Ideally each new testing page will be differentiated with a single parameter(just like Gmail). mysite.com/?ui=2 should give a different page. So for every view I need to write a decorator to load different templates based on the 'ui' parameter value. And I dont want to hard code any template names in decorators. So how would urls.py url pattern will be?
It's useful to take a step back and abstract what A/B testing is trying to do before diving into the code. What exactly will we need to conduct a test?
A Goal that has a Condition
At least two distinct Paths to meet the Goal's Condition
A system for sending viewers down one of the Paths
A system for recording the Results of the test
With this in mind let's think about implementation.
The Goal
When we think about a Goal on the web usually we mean that a user reaches a certain page or that they complete a specific action, for example successfully registering as a user or getting to the checkout page.
In Django we could model that in a couple of ways - perhaps naively inside a view, calling a function whenever a Goal has been reached:
def checkout(request):
a_b_goal_complete(request)
...
But that doesn't help because we'll have to add that code everywhere we need it - plus if we're using any pluggable apps we'd prefer not to edit their code to add our A/B test.
How can we introduce A/B Goals without directly editing view code? What about a Middleware?
class ABMiddleware:
def process_request(self, request):
if a_b_goal_conditions_met(request):
a_b_goal_complete(request)
That would allow us to track A/B Goals anywhere on the site.
How do we know that a Goal's conditions has been met? For ease of implementation I'll suggest that we know a Goal has had it's conditions met when a user reaches a specific URL path. As a bonus we can measure this without getting our hands dirty inside a view. To go back to our example of registering a user we could say that this goal has been met when the user reaches the URL path:
/registration/complete
So we define a_b_goal_conditions_met:
a_b_goal_conditions_met(request):
return request.path == "/registration/complete":
Paths
When thinking about Paths in Django it's natural to jump to the idea of using different templates. Whether there is another way remains to be explored. In A/B testing you make small differences between two pages and measure the results. Therefore it should be a best practice to define a single base Path template from which all Paths to the Goal should extend.
How should render these templates? A decorator is probably a good start - it's a best practice in Django to include a parameter template_name to your views a decorator could alter this parameter at runtime.
#a_b
def registration(request, extra_context=None, template_name="reg/reg.html"):
...
You could see this decorator either introspecting the wrapped function and modifying the template_name argument or looking up the correct templates from somewhere (like a Model). If we didn't want to add the decorator to every function we could implement this as part of our ABMiddleware:
class ABMiddleware:
...
def process_view(self, request, view_func, view_args, view_kwargs):
if should_do_a_b_test(...) and "template_name" in view_kwargs:
# Modify the template name to one of our Path templates
view_kwargs["template_name"] = get_a_b_path_for_view(view_func)
response = view_func(view_args, view_kwargs)
return response
We'd need also need to add some way to keep track of which views have A/B tests running etc.
A system for sending viewers down a Path
In theory this is easy but there are lot of different implementations so it's not clear which one is best. We know a good system should divide users evenly down the path - Some hash method must be used - Maybe you could use the modulus of memcache counter divided by the number of Paths - maybe there is a better way.
A system for recording the Results of the Test
We need to record how many users went down what Path - we'll also need access to this information when the user reaches the goal (we need to be able to say what Path they came down to met the Condition of the Goal) - we'll use some kind of Model(s) to record the data and either Django Sessions or Cookies to persist the Path information until the user meets the Goal condition.
Closing Thoughts
I've given a lot of pseudo code for implementing A/B testing in Django - the above is by no means a complete solution but a good start towards creating a reusable framework for A/B testing in Django.
For reference you may want to look at Paul Mar's Seven Minute A/Bs on GitHub - it's the ROR version of the above!
http://github.com/paulmars/seven_minute_abs/tree/master
Update
On further reflection and investigation of Google Website Optimizer it's apparent that there are gaping holes in the above logic. By using different templates to represent Paths you break all caching on the view (or if the view is cached it will always serve the same path!). Instead, of using Paths, I would instead steal GWO terminology and use the idea of Combinations - that is one specific part of a template changing - for instance, changing the <h1> tag of a site.
The solution would involve template tags which would render down to JavaScript. When the page is loaded in the browser the JavaScript makes a request to your server which fetches one of the possible Combinations.
This way you can test multiple combinations per page while preserving caching!
Update
There still is room for template switching - say for example you introduce an entirely new homepage and want to test it's performance against the old homepage - you'd still want to use the template switching technique. The thing to keep in mind is your going to have to figure out some way to switch between X number of cached versions of the page. To do this you'd need to override the standard cached middleware to see if their is a A/B test running on the requested URL. Then it could choose the correct cached version to show!!!
Update
Using the ideas described above I've implemented a pluggable app for basic A/B testing Django. You can get it off Github:
http://github.com/johnboxall/django-ab/tree/master
If you use the GET parameters like you suggsted (?ui=2), then you shouldn't have to touch urls.py at all. Your decorator can inspect request.GET['ui'] and find what it needs.
To avoid hardcoding template names, maybe you could wrap the return value from the view function? Instead of returning the output of render_to_response, you could return a tuple of (template_name, context) and let the decorator mangle the template name. How about something like this? WARNING: I haven't tested this code
def ab_test(view):
def wrapped_view(request, *args, **kwargs):
template_name, context = view(request, *args, **kwargs)
if 'ui' in request.GET:
template_name = '%s_%s' % (template_name, request.GET['ui'])
# ie, 'folder/template.html' becomes 'folder/template.html_2'
return render_to_response(template_name, context)
return wrapped_view
This is a really basic example, but I hope it gets the idea across. You could modify several other things about the response, such as adding information to the template context. You could use those context variables to integrate with your site analytics, like Google Analytics, for example.
As a bonus, you could refactor this decorator in the future if you decide to stop using GET parameters and move to something based on cookies, etc.
Update If you already have a lot of views written, and you don't want to modify them all, you could write your own version of render_to_response.
def render_to_response(template_list, dictionary, context_instance, mimetype):
return (template_list, dictionary, context_instance, mimetype)
def ab_test(view):
from django.shortcuts import render_to_response as old_render_to_response
def wrapped_view(request, *args, **kwargs):
template_name, context, context_instance, mimetype = view(request, *args, **kwargs)
if 'ui' in request.GET:
template_name = '%s_%s' % (template_name, request.GET['ui'])
# ie, 'folder/template.html' becomes 'folder/template.html_2'
return old_render_to_response(template_name, context, context_instance=context_instance, mimetype=mimetype)
return wrapped_view
#ab_test
def my_legacy_view(request, param):
return render_to_response('mytemplate.html', {'param': param})
Justin's response is right... I recommend you vote for that one, as he was first. His approach is particularly useful if you have multiple views that need this A/B adjustment.
Note, however, that you don't need a decorator, or alterations to urls.py, if you have just a handful of views. If you left your urls.py file as is...
(r'^foo/', my.view.here),
... you can use request.GET to determine the view variant requested:
def here(request):
variant = request.GET.get('ui', some_default)
If you want to avoid hardcoding template names for the individual A/B/C/etc views, just make them a convention in your template naming scheme (as Justin's approach also recommends):
def here(request):
variant = request.GET.get('ui', some_default)
template_name = 'heretemplates/page%s.html' % variant
try:
return render_to_response(template_name)
except TemplateDoesNotExist:
return render_to_response('oops.html')
A code based on the one by Justin Voss:
def ab_test(force = None):
def _ab_test(view):
def wrapped_view(request, *args, **kwargs):
request, template_name, cont = view(request, *args, **kwargs)
if 'ui' in request.GET:
request.session['ui'] = request.GET['ui']
if 'ui' in request.session:
cont['ui'] = request.session['ui']
else:
if force is None:
cont['ui'] = '0'
else:
return redirect_to(request, force)
return direct_to_template(request, template_name, extra_context = cont)
return wrapped_view
return _ab_test
example function using the code:
#ab_test()
def index1(request):
return (request,'website/index.html', locals())
#ab_test('?ui=33')
def index2(request):
return (request,'website/index.html', locals())
What happens here:
1. The passed UI parameter is stored in the session variable
2. The same template loads every time, but a context variable {{ui}} stores the UI id (you can use it to modify the template)
3. If user enters the page without ?ui=xx then in case of index2 he's redirected to '?ui=33', in case of index1 the UI variable is set to 0.
I use 3 to redirect from the main page to Google Website Optimizer which in turn redirects back to the main page with a proper ?ui parameter.
You can also A/B test using Google Optimize. To do so you'll have to add Google Analytics to your site and then when you create a Google Optimize experiment each user will get a cookie with a different experiment variant (according to the weight for each variant). You can then extract the variant from the cookie and display various versions of your application. You can use the following snippet to extract the variant:
ga_exp = self.request.COOKIES.get("_gaexp")
parts = ga_exp.split(".")
experiments_part = ".".join(parts[2:])
experiments = experiments_part.split("!")
for experiment_str in experiments:
experiment_parts = experiment_str.split(".")
experiment_id = experiment_parts[0]
variation_id = int(experiment_parts[2])
experiment_variations[experiment_id] = variation_id
However there is a django package that integrates well with Google Optimize: https://github.com/adinhodovic/django-google-optimize/.
And here is a blog post on how to use the package and how Google Optimize works: https://hodovi.cc/blog/django-b-testing-google-optimize/.