As you know, model managers can be overriden in Django. It's convenient to add custom filtration method there:
But these custom methods cannot be chained:
Overriding manager doesn't allow it, because after first manager method is invoked (
publishedin this case), we receive queryset as a result, which knows nothing about custom manager methods. So we have to add custom methods to queryset. This can look like this:
class ArticleQuerySet(models.query.QuerySet): def published(self): return self.filter("...") def old(self): return self.filter("...")
Now we need to make manager user this class. In order to do this, let's override manager's
class ArticleManager(models.Manager): def get_query_set(self): return ArticleQuerySet(self.model, using=self._db) class Article(models.Model): # ... objects = ArticleManager()
This allows to make queties like:
Here we invoke
all to get queryset instance, because this time manager doesn't have custom methods -
old. To avoid this, we can make manager look for undefined methods in queryset:
class ArticleManager(models.Manager): def get_query_set(self): return ArticleQuerySet(self.model, using=self._db) def getattr(self, key): return getattr(self.get_query_set(), key)
getattris only invoked when attribute is not found by usual means.
Manager can be further improved to be more generic:
class QuerySetManager(models.Manager): def init(self, queryset_class, args, **kwargs): self.queryset_class = queryset_class super(QuerySetManager, self).init(args, **kwargs) def get_query_set(self): return self.queryset_class(self.model, using=self._db) def getattr(self, key): return getattr(self.get_query_set(), key) # Теперь можно писать просто: # objects = QuerySetManager(ArticleQuerySet) #
In my current project I had a task to use twitter API. Twitter uses OAuth for authentication, which is pretty dreary. To avoid fiddling with it all the time, I've moved authentication to decorator. If key is available - nothing happens, just view is launched as usual. It's convenient that there's no need for additional twitter settings in user profile. Code is in article.
Lead management is an important part of the marketing strategy of every company of any size. Besides automating various business processes, privately-held organizations should consider implementing an IT solution that would help them manage their leads. So, how should you make a web-based leads management system for a University in order to significantly increase sales?
There are two most popular web frameworks in Python. There is the Django with lots of intelligent defaults and the Flask micro framework with complete freedom in the choice of modules. Let’s see, what django vs flask is in 2017.
It appears that not everyone knows that in python you can create classes dynamically without metaclasses. I'll show an example of how to do it.So we've learned how to use custom QuerySet to chain requests:Article.objects.old().public()Now we need to make it work for related objects:user.articles.old().public()This is done using use_for_related_fields, but it needs a little trick.