Hi,
Proposal:
Make it possible to use the same template block name twice, if the second
one is nested within the first one. Inheriting from the template fills in
the innermost block.
----------------------
Background (why is this useful?):
Say you have one base.html template defining a {% block content %}, and ten
templates inheriting from it and defining the contents of the block. Now
you decide that five of those templates actually should have a warning
message at the top, and you decide to make a new base_with_warning.html
template. You should should now be able to just change what block five of
the templates inherit from, add the warning to your new base template, and
be done with it?
Not really. Your base_with_warning.html would have to look like this:
{% extends "base.html" %}
{% block content %}
<div class="warning">Be careful when changing these settings!</div>
{% block content %}{% endblock %}
{% endblock %}
And this doesn't work in Django because duplicate block names are not
allowed. I think making this possible would make cases like the one I'm
describing above much easier to handle.
----------------------
Alternatives (this is how you should solve it instead...):
There are other ways to solve the problem I'm describing above. Let me list
a few and talk about the problems I see with them:
1) Create a new template block in base_with_warning.html and change the
five templates to use that block instead.
Problem: This puts the burden on developers to remember all kinds of
content blocks they have in this project, and change them depending on what
template they happen to be inherit from. The interface to the developer
working on a new child template is much cleaner if they know they can
always use the content block, and that the template they inherit from with
handle the rest.
2) Make a child templates call super, and put the warning div inside the
content block in base_with_warning.html.
Problem: It's very easy to forget calling super when making a new template.
It quickly becomes repetitive to type block.super in each of the templates.
Should I call super in the five templates without a warning too? Just to be
sure it isn't forgotten if someone changes the inherited template.
3) Use an include tag in each of the child templates instead of inheriting.
Problem: This is just as repetitive as copy-pasting the div to each of the
subtemplate, it's just the {% include "warning.html" %} is a shorter string
to copy-paste. As with all copy-paste, it makes it easy miss one instance
when changing the others. Not maintainable.
4) Use a template variable to decide whether to render the warning or not.
Problem: This moves the copy-paste to the view logic. Now I need to
remember to pass the right variable in the view instead, with the same
problem as with copy-paste above.
5) Write a custom template tag that does what I want.
Problem: I really don't know how to do this, and I haven't found someone
that has written a tag like that after are plenty of googling.
----------------------
Backwards compatibility (this will not break stuff!):
Since duplicate block names are not allowed today, this change would be
100% backwards compatible. Everything would continue working as it always
has.
----------------------
FAQ:
a) How would you inherit from a template with duplicate blocks with the
same name? This proposal only deals with the case where the first block is
defined inside the second block. If this happens the child templates
content should fill the INNER block, not the outer one. There would be no
way to override the outer block, since that would be shadowed by the
redefined inner block.
b) If we allow for multiple blocks with the same name, what should happen
with two blocks side by side (not nested)? We wouldn't allow that. This
proposal is only about duplicate blocks when nested inside eachother. All
other duplication would still yield the same error.
c) I have another suggestion that solves your problem without the problems
with 1) - 5) above, that doesn't require a change in django? That really
isn't a question, but fine :) Bring it on! I'm really interested in solving
the problem described in the background section in a clean way, not a
particular tech solution.
d) Do other people have this problem? I've found a few:
http://stackoverflow.com/questions/15448211/django-template-block-overriding/
-
http://stackoverflow.com/questions/8717521/django-multi-level-template-extends-and-nested-blocks
- This could also be used to handle nicely breadcrumbs in multiple levels.
You can probably think of more use-cases.
e) Is this the same as Ticket #4529:
https://code.djangoproject.com/ticket/4529 ? No. The code in that ticket
would still not work.
----------------------
Next steps:
I'm very eager to hear your thoughts on this, and maybe, if you think this
is a good idea, start to write up a ticket.
----------------------
Thanks for reading this far! I love the work you all do on making Django
better!
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