add mixins notes

Author: foobacca

DjangoConEurope2015/knives.rst

@@ -0,0 +1,2 @@
+Coding with knives (part 2)
+===========================

DjangoConEurope2015/mixins.rst

@@ -2,3 +2,71 @@ Demystifying mixins with Django
 ===============================
 
 Ana Balica
+@anabalica
+
+- mixins controlled way to add to your classes
+- NOT a special python construct - just ordinary python class
+- inherit from object
+
+- single responsibility
+- not meant to be extended to another Mixin
+- not meant to be instantiated
+- implemented using multiple inheritance
+  - order matters (method resolution order)
+
+Say copy/paste a feature between classes that are otherwise different
+
+.. code-block:: python
+
+    class MyMixin(object):
+        def mymethod(self):
+            pass
+
+    class Foo(BaseFoo, MyMixin):
+        # read as MyMixin is the base class, extended by BaseFoo, extended by Foo
+        # so this is bad
+        pass
+
+    class Foo(MyMixin, BaseFoo):
+        # better
+        pass
+
+extensions goes from right to left
+
+Class Based Views example
+
+.. code-block:: python
+
+    class LoginRequiredMixin(object):
+        def dispatch(self, request, *args, **kwargs):
+            if not request.user.is_authenticated():
+                raise PermissionDenied
+            return super(LoginRequiredMixin, self).dispatch(request, *args, **kwargs)
+
+    class AboutView(LoginRequiredMixin, TemplateView):
+        template_name = "about.html"
+
+- alternative - TemplateView <- LoginRequiredTemplateView <- AboutView
+- but then DetailView needs LoginRequiredDetailView, UpdateView ... - duplicated code
+- so Mixin approach reduces duplication
+
+Useful methods in class based views
+
+- dispatch() - check permissions
+- get_context_data() - add more data to the context
+- get_template_names() - more flexible selection of template
+
+How to learn
+
+- Just read the source code
+- https://docs.djangoproject.com/en/1.8/topics/class-based-views/mixins/
+- http://ccbv.co.uk/
+
+- django-braces is a package with lots of useful mixins
+- don't do too much chaining of mixins - hard to understand execution flow
+
+Summary
+
+- single responsibility
+- plug-in functionality
+- isn't creating a subtyping relation (so not SOLID, breaks Liskov)