"get_context_data" should follow MRO
|Reported by:||linovia||Owned by:||nobody|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
Description (last modified by )
Actually, mixins do not allow to cumulate the context building.
class CommentMixin(FormMixin, SingleObjectMixin): pass
In that case, we expect both FormMixin and SingleObjectMixin to build their context.
However, as none of them use super in their get_context_data do use super, we only get the FormMixin context.
The reason to use super here is not to call the parent get_context_data but the next class in MRO.
class A(object): def a(self): print "A" if hasattr(super(A, self), 'a'): super(A, self).a() class B(object): def a(self): print "B" if hasattr(super(B, self), 'a'): super(B, self).a() class C(object): def a(self): print "C" class D(B, A): pass class E(C, A): pass print "MRO:", [x.__name__ for x in D.__mro__] d = D() d.a() print "MRO:", [x.__name__ for x in E.__mro__] e = E() e.a()
With that example, one can see that d calls both B then A while e only calls C.
While this might usually be unnoticed, it prevents Mixin to be chained.
For example, mixing a single object item with a list (for a shop: one category with the associated products, for a bug tracker: a milestone with the associated tickets) or a single item with a form such as a post with a comment form.