[DjangoCon Europe 2015] Demystifying Mixins with Django

"Demystifying mixins with Django" is a 15 minutes talk I presented at DjangoCon 2015 in Cardiff, UK.

Transcript

1. Demystifying Mixins with Django
2. @anabalica
3. Mixins are a controlled way of adding functionality to classes.
4. Mixins are not special language constructs.
5. In fact, mixins are ordinary Python classes. 1 class SomeMixin(object): 2 """My smart mixin""" 3 4 def test_method(self): 5 pass
6. Why use mixins? to improve modularity
7. When to use mixins? want to reuse a particular feature in a lot of different classes
8. Properties • single responsibility • not meant to be extended • not meant to be instantiated
11. In Python the concept of mixins is implemented using multiple inheritance.
12. Order matters
13. 1 class Foo(BaseFoo, SomeMixin): 2 pass base class mixin
14. 1 class Foo(BaseFoo, SomeMixin): 2 pass
15. 1 class Foo(SomeMixin, BaseFoo): 2 pass
16. 1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(TemplateView): 6 template_name = "about.html"
17. 1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(SomeMixin, TemplateView): 6 template_name = "about.html"
18. My first mixin
19. 1 # some_app/views.py 2 3 4 class LoginRequiredMixin(object): 5
20. 1 # some_app/views.py 2 3 4 class LoginRequiredMixin(object): 5 6 def dispatch(self, request, *args, **kwargs): 7
21. 1 # some_app/views.py 2 from django.core.exceptions import PermissionDenied 3 4 5 class LoginRequiredMixin(object): 6 7 def dispatch(self, request, *args, **kwargs): 8 if not request.user.is_authenticated(): 9 raise PermissionDenied 10
22. 1 # some_app/views.py 2 from django.core.exceptions import PermissionDenied 3 4 5 class LoginRequiredMixin(object): 6 7 def dispatch(self, request, *args, **kwargs): 8 if not request.user.is_authenticated(): 9 raise PermissionDenied 10 11 return super(LoginRequiredMixin, self).\ 12 dispatch(request, *args, **kwargs) 13
23. 1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(LoginRequiredMixin, TemplateView): 6 template_name = "about.html"
24. LoginRequiredMixin TemplateView AboutView
25. LoginRequiredMixin DetailView AboutView
26. ListView LoginRequiredListView AboutView CreateView LoginRequiredCreateView AboutView DetailView LoginRequiredDetailView AboutView FormView LoginRequiredFormView AboutView MyView LoginRequiredMyView AboutView TemplateView LoginRequiredTemplateView AboutView
27. LoginRequiredMixin TemplateView AboutView
28. dispatch() get_context_data() get_template_names() check if user is logged in, has permission add new data to the context add more flexibility to the template names
29. 1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(TemplateView): 6 template_name = "about.html"
30. dispatch() get_context_data() get_template_names() check if user is logged in, has permission add new data to the context add more flexibility to the template names
31. docs.djangoproject.com/en/1.8/ref/ class-based-views/base/
32. docs.djangoproject.com/en/1.8/ref/ class-based-views/base/
33. docs.djangoproject.com/en/1.8/topics/ class-based-views/mixins/
34. docs.djangoproject.com/en/1.8/topics/ class-based-views/mixins/
35. ccbv.co.uk/
36. django-braces Access Mixins Form Mixins Other Mixins
37. With great power comes great responsibility
38. Recap • single responsibility • plug-in functionality • isn’t creating a subtyping relation
39. Go back to your views and start writing mixins to clean up the code.