django add filters in template is not working expectedly

Question

I am a Django and Python beginner, and I encountered a problem while using Django. I hope to use a filter in the template to get the string I need, but the result below is not what I expected.

# filter definition

@register.filter
def to_class_name(obj):
    return obj.__class__.__name__

# HTML template for UpdateView (This template will be used by multiple models.)
# object = Order()

{{ object|to_class_name }} #reulst: Order

{{ 'wms'|add:object|to_class_name }} #result: str, expect: object

I roughly understand that the issue lies with the order, but it seems I can't add parentheses to modify it.

{{ 'wms'|add:(object|to_class_name) }} #cause SyntaxError

Is there any way to solve this problem? Or is there a better way to determine the page data I need to output based on the model class when multiple models share one template? Thank you all.

Answer 1

I roughly understand that the issue lies with the order, but it seems I can't add parentheses to modify it.

You can use variables. link

One way is to use with tag.

it caches a complex variable under a simpler name. The variable is available until the {% endwith %} tag appears.

eg.

{% with firstname="Tobias" %}
<h1>Hello {{ firstname }}, how are you?</h1>
{% endwith %}

In your case, something like this

{% with class_name=object|to_class_name %}
   {{ 'wms'|add:class_name }}
{% endwith %}

Another approach is to use firstof tag. link

{% firstof object|to_class_name as class_name %}
{{ 'wms'|add:class_name }}