Path parameters for custom pages

[simonw]

Custom pages let you e.g. create a templates/pages/about.html page and have it automatically served at /about.

It would be useful if these pages could capture path patterns. I like the Python format string syntax for this (also used by Starlette): /foo/bar/{slug}.

So... how about embedding those patterns in the filenames themselves?

templates/pages/museums/{slug}.html

Would capture any hits to /museums/something and use that page to serve them.

[simonw]

I created a template file called templates/pages/museums/{slug}.html and used the debugger to see if Jinja could see it. This worked:

(Pdb) self.ds.jinja_env.list_templates()
['500.html', '_codemirror.html', '_codemirror_foot.html', '_description_source_license.html', '_footer.html',
'_table.html', 'allow_debug.html', 'base.html', 'database.html', 'default:500.html', 'default:_codemirror.html',
'default:_codemirror_foot.html', 'default:_description_source_license.html', 'default:_footer.html',
'default:_table.html', 'default:allow_debug.html', 'default:base.html', 'default:database.html',
'default:index.html', 'default:logout.html', 'default:messages_debug.html', 'default:patterns.html',
'default:permissions_debug.html', 'default:query.html', 'default:row.html', 'default:show_json.html',
'default:table.html', 'forbidden.html', 'index.html', 'logout.html', 'messages_debug.html',
'pages/about.html', 'pages/museums/{slug}.html', 'patterns.html', 'permissions_debug.html',
'query.html', 'row.html', 'show_json.html', 'table.html']

The pages/museums/{slug}.html template is in that list.

Here's the implementation of that list_templates() method - it does some filesystem walking so it may be a bit expensive to run it on every request: https://github.com/pallets/jinja/blob/ca8b0b0287e320fe1f4a74f36910ef7ae3303d99/src/jinja2/loaders.py#L197-L212

But caching it would be pretty easy - either until the server is restarted or as an in-memory cache for a few seconds.

[simonw]

These templates will need a way to raise a 404 - so that if the template itself is deciding if the page exists (for example using datasette-template-sql or the proposed datasette.get() method from #943 or the graphql() template function in simonw/datasette-graphql#50) it can return a regular 404 page.

This can imitate the custom_redirect() function from https://docs.datasette.io/en/stable/custom_templates.html#custom-redirects:

{{ custom_redirect("https://github.com/simonw/datasette", 301) }}

It could be as simple as this:

{{ raise_404("Museum not found") }}

[simonw]

I'm going to cache the list_templates() result in memory. If you want to add a new template-defined route you will need to restart the server. I think that's acceptable.

[simonw]

Actually don't need {{ raise_404("Museum not found") }} because we already have {{ custom_status(404) }}.

[simonw]

Having tried this out I think it does need a raise_404() mechanism - which needs to be smart enough to trigger the default 404 handler without accidentally going into an infinite loop.