I am working on a django project that requires much of the common page data be dynamic. Things that appear on every page, such as the telephone number, address, primary contact email etc all need to be editable via the admin panel, so storing them in the settings.py file isn't going to work.
To get around this, I created a custom context processor which acts as an abstract reference to my "Live Settings" model. The model looks like this:
class LiveSetting(models.Model):
id = models.AutoField(primary_key=True)
title = models.CharField(max_length=255, blank=False, null=False)
description = models.TextField(blank=True, null=True)
key = models.CharField(max_length=100, blank=False, null=False)
value = models.CharField(max_length=255, blank=True)
And the context processor like so:
from livesettings.models import LiveSetting
class LiveSettingsProcessor(object):
def __getattr__(self, request):
val = LiveSetting.objects.get(request)
setattr(self, val.key, val.value)
return val.value
l = LiveSettingsProcessor()
def livesetting_processors(request):
return {'settings':l}
It works really nicely, and in my template I can use {{ settings.primary_email }} and get the corresponding value from the database.
The problem with the above code is it handles each live setting request individually and will hit the database each time my {{ settings.*}} tag is used in a template.
Does anyone have any idea if I could make this process lazy, so rather than retrieve the value and return it, it instead updates a QuerySet then returns the results in one hit just before the page is rendered?
You are trying to invent something complex and these is no reason for that. Something as simple as this will work fork you good enough:
def livesetting_processors(request):
settings = LiveSetting.objects.get(request)
return {'settings':settings}
EDIT:
This is how you will solve your problem in current implementation:
class LiveSettingsProcessor(object):
def __getattr__(self, request):
val = getattr(self, '_settings', LiveSetting.objects.get(request))
setattr(self, val.key, val.value)
return val.value
#Hanpan, I've updated my answer to show how you can to solve your problem, but what I want to say is that things you are trying to achieve does not give any practical win, however it increase complexity ant it takes your time. It might also be harder to setup cache on all of this later. And with caching enabled this will not give any improvements in performance at all.
I don't know if you heard this before: premature optimization is the root of evil. I think this thread on SO is useful to read: https://stackoverflow.com/questions/211414/is-premature-optimization-really-the-root-of-all-evil
Maybe you could try Django's caching?
In particular, you may want to check out the low-level caching feature. It seems like it would be a lot less work than what you plan on.
Related
The below model have EditorManager,
class EditorManager(models.Manager):
def get_queryset(self):
return super().get_queryset().filter(role='E')
class Person(models.Model):
first_name = models.CharField(max_length=50)
role = models.CharField(max_length=1, choices=[('A', _('Author')), ('E', _('Editor'))])
people = models.Manager()
editors = EditorManager()
If I query Person.objects.filter(role='E') or Person.editors.all() I gets same result.
then, Why do we go for writing EditorManager() ?
The above code is from Django documentation (https://docs.djangoproject.com/en/3.0/topics/db/managers/).
As mentioned in the Documentation:
using multiple managers on the same model. You can attach as many Manager() instances to a model as you’d like. This is a non-repetitive way to define common “filters” for your models.
Since you just have one action, it may be hard for you to see the benefits. However, as your code gets larger, say:
good = Book.objects.filter(author="PersonA", stars=5).order_by("-date_created").exclude(outdated=True)
normal = Book.objects.filter(author="PersonA", stars=3).order_by("-date_created").exclude(outdated=True)
bad = Book.objects.filter(author="PersonA", stars=1).order_by("-date_created").exclude(outdated=True)
You can see that's an awful lot of code. With managers, you can do something like this:
class AuthorAManager(models.Manager):
def get_queryset(self):
return super().get_queryset().filter(author="PersonA").order_by("-date_created").exclude(outdated=True)
class Book(models.Model):
# ...
author_a = AuthorAManager()
good = Book.author_a.filter(stars=5)
normal = Book.author_a.filter(stars=3)
bad = Book.author_a.filter(stars=1)
Overall, it can make your code look a lot cleaner and understandable. As you said, you can't see the difference right now as you haven't gone into complex/repeating handles, but as your project expands, I'd say it's a worthwhile investment.
I have a database containing a list of ingredients. I'd like to avoid duplicate entries in this table. I don't want to use the unique keyword for 2 reasons :
My uniqueness constraints are a bit more sophisticated than a mere =
I don't want to raise an exception when a pre-existing ingredient model is created, instead I just want to return that model, so that I can write Ingredient(ingredient_name='tomato') and just go on with my day rather than encapsulating all of that in a try clause. This will allow me to easily add ingredients to my recipe table on the fly.
One solution is simply to have a wrapper function like create_ingredient, but I don't find that to be particularly elegant and more specifically it's not robust to some other developer down the line simply forgetting to use the wrapper. So instead, I'm playing around with the pre_init and post_init signals.
Here's what I have so far :
class Ingredient(models.Model):
ingredient_name = models.CharField(max_length=200)
recipes = models.ManyToManyField(Recipe,related_name='ingredients')
def __str__(self):
return self.ingredient_name
class Name(models.Model):
main_name = models.CharField(max_length=200, default=None)
equivalent_name = models.CharField(max_length=200, primary_key=True, default=None)
def _add_ingredient(sender, args, **kwargs):
if 'ingredient_name' not in kwargs['kwargs'] :
return
kwargs['kwargs']['ingredient_name'] = kwargs['kwargs']['ingredient_name'].lower()
# check if equivalent name exists, make this one the main one otherwise
try:
kwargs['kwargs']['ingredient_name'] = Name.objects.filter(
equivalent_name=kwargs['kwargs']['ingredient_name']
)[0].main_name
except IndexError:
name = Name(main_name=kwargs['kwargs']['ingredient_name'],
equivalent_name=kwargs['kwargs']['ingredient_name'])
name.save()
pre_init.connect(_add_ingredient, Ingredient)
So far so good. This actually works and will replace ingredient_name when needed before the model is initialized. Now what I'd like is to check if the ingredient in question already exists and have the initializer return it if it does. I think I need to play around with post_init to do this but I don't know how to modify the particular instance that's being created. Here's what I mean by that :
def _finalize_ingredient(sender, instance, **kwargs):
try:
# doesn't work because of python's "pass arguments in python's super unique way of doing things" thing
instance = Ingredient.objects.filter(ingredient_name=instance.ingredient_name)[0]
except IndexError:
pass
post_init.connect(_finalize_ingredient, Ingredient)
As I've commented, I don't expect this to work because instance = ... doesn't actually modify instance, it just reassigns the variable name (incidentally if you try to run this all sorts of terrible things happen which I don't care to understand because I know this is flat out wrong). So how do I actually do this ? I really hope wrapper functions aren't the cleanest option here. I'm a big fan of OOP and gosh darn it I want an OOP solution to this (which, as I've said, I think in the long run would be much more robust and safer than wrappers).
I realize of course that I can add an add_ingredient method to Recipe which will do all of this for me, but I really like the idea of containing all of this in my Ingredient class as it will guarantee the proper database behavior under any circumstance. I'm also curious as to know if/how the post_init method can be used to completely override the created object for a given circumstance.
By the way, some of you may be wondering why I don't have a ForeignKey entry in my Name class that would connect the Name table to the Ingredient table. After all, isn't this what my check is essentially accomplishing in my _add_ingredient method ? One of the reasons is that if I do this then I end up with the same problem I'm trying to solve here : If I want to create an ingredient on the fly to add it to my recipe, I could simply create a Name object when creating an Ingredient object, but that would raise an exception if it corresponds to a main_name that is already in use (rather than simply returning the object I need).
I believe you are looking for get_or_create(), which is already a built-in in Django.
You mention:
One solution is simply to have a wrapper function like create_ingredient, but I don't find that to be particularly elegant and more specifically it's not robust to some other developer down the line simply forgetting to use the wrapper.
Well, look at it the other way around. What if you actually need to create a "duplicate" ingredient? Then it is nice to have the possibility.
I've come up with something that is as elegant and robust as I think it's possible to be given what I'm after. I've still had to define an add_ingredient method, but I still have the robustness that I need. I've made it so that it can be generalized to any class with a primary key, and the Name table will contain the info that will define the name uniqueness of any table :
class Name(models.Model):
main_name = models.CharField(max_length=200, default=None)
equivalent_name = models.CharField(max_length=200, primary_key=True, default=None)
def _pre_init_unique_fetcher(sender, args, **kwargs):
pk_name = sender._meta.pk.name
if pk_name not in kwargs['kwargs'] :
return
kwargs['kwargs'][pk_name] = kwargs['kwargs'][pk_name].lower()
# check if equivalent name exists, make this one the main one otherwise
try:
kwargs['kwargs'][pk_name] = Name.objects.filter(
equivalent_name=kwargs['kwargs'][pk_name]
)[0].main_name
except IndexError:
name = Name(main_name=kwargs['kwargs'][pk_name],
equivalent_name=kwargs['kwargs'][pk_name])
name.save()
sender._input_dict = kwargs['kwargs']
def _post_init_unique_fetcher(sender, instance, **kwargs):
pk_name = sender._meta.pk.name
pk_instance = instance.__dict__[pk_name]
filter_dict = {}
filter_dict[pk_name] = pk_instance
try:
post_init.disconnect(_post_init_unique_fetcher,sender)
instance.__dict__ = sender.objects.filter(**filter_dict)[0].__dict__
post_init.connect(_post_init_unique_fetcher, sender)
for key in sender._input_dict:
instance.__dict__[key] = sender._input_dict[key]
del sender._input_dict
except IndexError:
post_init.connect(_post_init_unique_fetcher, sender)
except:
post_init.connect(_post_init_unique_fetcher, sender)
raise
unique_fetch_models = [Ingredient, Recipe, WeekPlan]
for unique_fetch_model in unique_fetch_models :
pre_init.connect(_pre_init_unique_fetcher, unique_fetch_model)
post_init.connect(_post_init_unique_fetcher, unique_fetch_model)
Now what this will do is load up any new model with the pre-existing data of the previous model (rather than the default values) if one with the same name exists. The reason I still need an add_ingredient method in my Recipe class is because I can't call Ingredient.objects.create() for a pre-existing ingredient without raising an exception despite the fact that I can create the model and immediately save it. This has to do with how Django handles the primary_key designation : if you create the model then save it, it assumes you're just updating the entry if it already exists with that key, and yet if you create it, it tries to add another entry and that conflicts with the primary_key designation. So now I can do things like recipe.add_ingredient(Ingredient(ingredient_name='tomato', vegetarian=True)).
I have two basic models, a Command and a Flow. Flows can contain a series of commands or other nested Flows. So any given Flow can have a list of children that are either Step or Flow types. (This is similar to Files and Directories you might model in a file system.)
I've tried to model this using ContentTypes, Generic relations, and mptt (which doesn't allow for generic content types AFAIK) but have had no success. Here are my basic models:
class Step(models.Model):
parent = models.ForeignKey('Step', null=True)
name = models.CharField( max_length=100 )
start_time = models.DateTimeField(null=True)
end_time = models.DateTimeField(null=True)
state = models.CharField( max_length=1, default='u' )
class Flow(Step):
type = models.CharField( max_length=1 )
def getChildren(self):
# todo: the steps returned here need to be sorted by their order in the flow
return Step.objects.filter(parent_id=self.parent_id)
def run(self):
for child in self.getChildren():
print("DEBUG: run method processing a {0}".format(child.__class__.__name__) )
# if this is a flow, run it
# else if it's a command, execute it
class Command(Step):
exec_string = models.TextField()
I want to be able to create Flows in my app, query the children, then process each child differently depending on its type (commands get executed, flows get recursively processed.)
I would appreciate any correction of my code above which would make this possible or even comments that I'm approaching this problem the complete wrong way for Django.
Edit: I should add that I'm using Python 3.3 and Django dev (to be named 1.6)
I finally found an answer via some great help on IRC here and wanted to share it in case anyone else had the same problem.
The only thing I had to ultimately change was Flow.getChildren().
def getChildren(self):
# Get a list of all the attrs relating to Child models.
child_attrs = dict(
(rel.var_name, rel.get_cache_name())
for rel in Step._meta.get_all_related_objects()
if issubclass(rel.field.model, Step) and isinstance(rel.field, models.OneToOneField)
)
objs = []
for obj in self.children.all().select_related(*child_attrs.keys()):
# Try to find any children...
for child in child_attrs.values():
sobj = obj.__dict__.get(child)
if sobj is not None:
break
objs.append(sobj)
return objs
If anyone has a cleaner solution I'd love to see it, especially since this seems like a lot of work for something it seems like the framework should handle more directly.
The thing that jumps out at me is "return Step.objects.filter(parent_id=self.parent_id)". I believe it should be "return Step.objects.filter(parent__pk=self.parent.pk)"
I am sure that someone has a pluggable app (or tutorial) out there that approximates this, but I have having trouble finding it: I want to be able to track the number of "views" a particular object has (just like a question here on stackoverflow has a "view count").
If the user isn't logged in, I wouldn't mind attempting to place a cookie (or log an IP) so they can't inadvertently run up the view count by refreshing the page; and if a user is logged in, only allow them one "view" across sessions/browsers/IP addresses. I don't think I need it any fancier than that.
I figure the best way to do this is with Middleware that is decoupled from the various models I want to track and using an F expression (of sorts) -- other questions on StackOverflow have alluded to this (1), (2), (3).
But I wonder if this code exists out in the wild already -- because I am not the savviest coder and I'm sure someone could do it better. Smile.
Have you seen it?
I am not sure if it's in the best taste to answer my own question but, after a bit of work, I put together an app that solves the problems in earnest: django-hitcount.
You can read about how to use it at the documentation page.
The ideas for django-hitcount came came from both of my two original answers (Teebes -and- vikingosegundo), which really got me started thinking about the whole thing.
This is my first attempt at sharing a pluggable app with the community and hope someone else finds it useful. Thanks!
You should use the django built-in session framework, it already does a lot of this for you. I implemented this in the following way with a Q&A app where I wanted to track views:
in models.py:
class QuestionView(models.Model):
question = models.ForeignKey(Question, related_name='questionviews', on_delete=models.CASCADE)
ip = models.CharField(max_length=40)
session = models.CharField(max_length=40)
created = models.DateTimeField(default=datetime.datetime.now())
in views.py:
def record_view(request, question_id):
question = get_object_or_404(Question, pk=question_id)
if not QuestionView.objects.filter(
question=question,
session=request.session.session_key):
view = QuestionView(question=question,
ip=request.META['REMOTE_ADDR'],
created=datetime.datetime.now(),
session=request.session.session_key)
view.save()
return HttpResponse(u"%s" % QuestionView.objects.filter(question=question).count())
Vikingosegundo is probably right though that using content-type is probably the more reusable solution but definitely don't reinvent the wheel in terms of tracking sessions, Django already does that!
Last thing, you should probably have the view that records the hit be either called via Ajax or a css link so that search engines don't rev up your counts.
Hope that helps!
You could create a generic Hit model
class Hit(models.Model):
date = models.DateTimeField(auto_now=True)
content_type = models.ForeignKey(ContentType)
object_id = models.PositiveIntegerField()
content_object = generic.GenericForeignKey('content_type', 'object_id')
In your view.py you write this function:
def render_to_response_hit_count(request,template_path,keys,response):
for key in keys:
for i in response[key]:
Hit(content_object=i).save()
return render_to_response(template_path, response)
and the views that you are interested in return
return render_to_response_hit_count(request, 'map/list.html',['list',],
{
'list': l,
})
This approach gives you the power, not only to count the hit, but to filter the hit-history by time, contenttype and so on...
As the hit-table might be growing fast, you should think about a deletion strategy.
I know this question is an old one and also thornomad has put an app to solve the problem and inspire me with me solution. I would like to share this solution since I didn't find much information about this topic and it may help someone else.
My approach is to make a generic model can be used with any view based on the view path (url).
models.py
class UrlHit(models.Model):
url = models.URLField()
hits = models.PositiveIntegerField(default=0)
def __str__(self):
return str(self.url)
def increase(self):
self.hits += 1
self.save()
class HitCount(models.Model):
url_hit = models.ForeignKey(UrlHit, editable=False, on_delete=models.CASCADE)
ip = models.CharField(max_length=40)
session = models.CharField(max_length=40)
date = models.DateTimeField(auto_now=True)
views.py
def get_client_ip(request):
x_forwarded_for = request.META.get('HTTP_X_FORWARDED_FOR')
if x_forwarded_for:
ip = x_forwarded_for.split(',')[0]
else:
ip = request.META.get('REMOTE_ADDR')
return ip
def hit_count(request):
if not request.session.session_key:
request.session.save()
s_key = request.session.session_key
ip = get_client_ip(request)
url, url_created = UrlHit.objects.get_or_create(url=request.path)
if url_created:
track, created = HitCount.objects.get_or_create(url_hit=url, ip=ip, session=s_key)
if created:
url.increase()
request.session[ip] = ip
request.session[request.path] = request.path
else:
if ip and request.path not in request.session:
track, created = HitCount.objects.get_or_create(url_hit=url, ip=ip, session=s_key)
if created:
url.increase()
request.session[ip] = ip
request.session[request.path] = request.path
return url.hits
I did this by creating a model PageViews and making a column "Hits" in it. Every time when Homepage url is hit. I increment the first and only row of column Hit and render it to the template. Here how it looks.
Views.py
def Home(request):
if(PageView.objects.count()<=0):
x=PageView.objects.create()
x.save()
else:
x=PageView.objects.all()[0]
x.hits=x.hits+1
x.save()
context={'page':x.hits}
return render(request,'home.html',context=context)
Models.py
class PageView(models.Model):
hits=models.IntegerField(default=0)
I did it using cookies. Don't know if it's a good idea to do that or not. The following code looks for an already set cookie first if it exists it increases the total_view counter if it is not there the it increases both total_views and unique_views. Both total_views and unique_views are a field of a Django model.
def view(request):
...
cookie_state = request.COOKIES.get('viewed_post_%s' % post_name_slug)
response = render_to_response('community/post.html',context_instance=RequestContext(request, context_dict))
if cookie_state:
Post.objects.filter(id=post.id).update(total_views=F('total_views') + 1)
else:
Post.objects.filter(id=post.id).update(unique_views=F('unique_views') + 1)
Post.objects.filter(id=post.id).update(total_views=F('total_views') + 1)
response.set_cookie('viewed_post_%s' % post_name_slug , True, max_age=2678400)
return response
I'm going to post some incomplete code to make the example simple. I'm running a recursive function to compute some metrics on a hierarchical structure.
class Category(models.Model):
parent = models.ForeignKey('self', null=True, blank=True, related_name='children', default=1)
def compute_metrics(self, shop_object, metric_queryset=None, rating_queryset=None)
if(metric_queryset == None):
metric_queryset = Metric.objects.all()
if(rating_queryset == None):
rating_queryset = Rating.objects.filter(shop_object=shop_object)
for child in self.children.all():
do stuff
child_score = child.compute_metrics(shop_object, metric_queryset, rating_queryset)
metrics_in_cat = metric_queryset.filter(category=self)
for metric in metrics_in_cat
do stuff
I hope that's enough code to see what's going on. What I'm after here is a recursive function that is only going to run those queries once each, then pass the results down. That doesn't seem to be happening right now and it's killing performance. Were this PHP/MySQL (as much as I dislike them after working with Django!) I could just run the queries once and pass them down.
From what I understand of Django's querysets, they aren't going to be evaluated in my if queryset == None then queryset=stuff part. How can I force this? Will it be re-evaluated when I do things like metric_queryset.filter(category=self)?
I don't care about data freshness. I just want to read from the DB once for each of metrics and rating, then filter on them later without hitting the DB again. It's a frustrating problem that feels like it should have a very simple answer. Pickling looks like it could work but it's not very well explained in the Django documentation.
I think the problem here is you are not evaluating the queryset until after your recursive call. If you use list() to force the evaluation of the queryset then it should only hit the database once. Note you will have to change the metrics_in_cat line to a python level filter rather than using queryset filters.
parent = models.ForeignKey('self', null=True, blank=True, related_name='children', default=1)
def compute_metrics(self, shop_object, metric_queryset=None, rating_queryset=None)
if(metric_queryset is None):
metric_queryset = list([Metric.objects.all())
if(rating_queryset is None):
rating_queryset = list(Rating.objects.filter(shop_object=shop_object))
for child in self.children.all():
# do stuff
child_score = child.compute_metrics(shop_object, metric_queryset, rating_queryset)
# metrics_in_cat = metric_queryset.filter(category=self)
metrics_in_cat = [m for m in metric_queryset if m.category==self]
for metric in metrics_in_cat
# do stuff