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djangodjango-templatesdjango-1.4

Django template conditional variable assignment


I want to assign a variable do different values depending on if a variable exists, is this possible? My non working example might make it clearer:

{% if username %}
    {% with menu_user=username %}
{% elif recent_users %}
    {% with sorted_users=recent_users|dictsortreversed:"timestamp" %}
    {% with menu_user=sorted_users.0.username %}
{% endif %}
{% if menu_user %}
    <div id="menu">
        <ul>
            <li><a href="/user/{{ menu_user|urlencode }}">Profile</a></li>
            <li><a href="/user/{{ menu_user|urlencode }}/products/">Products</a></li>
        </ul>
    </div>
{% endif %}
{% if recent_users %}
    {% endwith %}
{% endif %}
    {% endwith %}

Pseudocode of what I try to do:

if username:
    menu_user = username
elif recent_users:
    menu_user = sorted(recent_users)[0]['username']

if menu_user:
    <div id="menu">
        <ul>
            <li><a href="/user/{{ menu_user|urlencode }}">Profile</a></li>
            <li><a href="/user/{{ menu_user|urlencode }}/products/">Products</a></li>
        </ul>
    </div>

Solution

  • update Then its better to customize a template tag like

    @register.inclusion_tag('menu_snippet.html')  # or you could use takes_context=True and fetch values from the context
    def render_menu(username, recent_users):
        if username:
            menu_user = username
        elif recent_users:
            # sorted here could be replaced by min or QuerySet method, it depends
            # for example: 
            # menu_user = min(recent_users, key=lambda u:u.timestamp).username
            menu_user = sorted(recent_users)[0]['username']
        return {'menu_user':menu_user}
    
    # in template, it looks like
    {% render_menu username recent_users %}
    

    Putting the code in the view is much better. Just as your pseudocode, clean and readable.

    If you still want to write template, I prefer something like

    {% if username %}
        <div id="menu">
            <ul>
                <li><a href="/user/{{ username|urlencode }}">Profile</a></li>
                <li><a href="/user/{{ username|urlencode }}/products/">Products</a></li>
            </ul>
        </div>
    {% else %}
        {% if recent_users %}
        {% with sorted_users=recent_users|dictsortreversed:"timestamp" %}
        {% with menu_user=sorted_users.0.username %}
        <div id="menu">
            <ul>
                <li><a href="/user/{{ menu_user|urlencode }}">Profile</a></li>
                <li><a href="/user/{{ menu_user|urlencode }}/products/">Products</a></li>
            </ul>
        </div>
        {% endwith %}{% endwith %}
        {% endif %}
    {% endif %}
    

    Depends on your actual usage, customized template tag or the include tag are also possibly useful.