before_first_request and url_for

[phistrom]

I used to use before_first_request to set up a sort of navigation config.

@app.before_first_request
def _setup_navigation(app):
    app.config['navigation'] = [
        {'name': 'Home', 'url': url_for('mysite.home', _external=False)},
        {'name': 'About', 'url': url_for('mysite.about', _external=False)},
        ...
    ]

and then I have a navbar.jinja2 that iterates through this creating links based on the list found in app.config.navigation like

<div class="navbar" id="main-nav">
    <ul class="nav navbar-nav">
    {% for nav in config.navigation %}
        <li><a href="{{ nav.url }}">{{ nav.name }}</a></li>
    {% endfor %}
    </ul>
</div>

But then before_first_request was deprecated. So I am trying to update to use the app factory pattern. But I cannot use url_for outside a request context unless I specify a SERVER_NAME. But then it's more difficult to do local debugging since I can't just go to localhost:8000 anymore because that doesn't match the SERVER_NAME.

To get around this, I have just added a before_request decorator and wrapped it in a test for the existence of my app.config['navigation'] key.

Perhaps url_for could be relaxed to not need a SERVER_NAME when _external=False?

[davidism]

You can set the SERVER_NAME to localhost:8000 during development.

https://flask.palletsprojects.com/en/2.2.x/appcontext/#manually-push-a-context shows how to push an app context during the factory function.

[tachyondecay]

It’s unclear to me why you aren't just generating these on each request (using before_request) or doing it in the template itself (url_for is automatically injected into the template environment for you). This should not create much of a performance impact.

[phistrom]

It probably wouldn't create much performance impact to do it every time. In most places I use url_for directly in my templates. It just felt easier to make a nice loop in the jinja2 template than to copy and paste the same HTML markup for each link I wanted to add. Regenerating the navigation data structure on every request felt wasteful, and I believe it was an argument for deprecating before_first_request in the first place. I suppose I'll just rewrite it to have just the endpoint string (i.e. 'mysite.about') and then have <a href="{{ url_for(nav.url, _external=False) }}">{{ nav.name }}</a> in the navbar.jinja2 template.

To be clear, I'm fine with the deprecation, but am I wrong for thinking that url_for doesn't need a SERVER_NAME when generating _external=False URLs?