Custom template filter syntax in django

Question

So i have created a custom filter:

@register.filter(name='field_values')
def field_values(model, field):
    return model.objects.values_list(field, flat=True)

that takes model class value and a field for an argument and returns a list of model objects for that particular field. Here is the template where I try to call it.

<tr>
    {% for field in fields %}
            <td>{{ model_class|field_values: field }} </td>
     {% endfor %}
</tr>

model_class is a dynamically created model in the views as such

views.py
...
if form.is_valid(): # All validation rules pass
    model_classes_field = form.cleaned_data['model_classes_field']
    model_class = get_model('Directories', model_classes_field)

I was expecting everything to run smoothly but instead I get a "*field_values requires 1 arguments, 0 provided*" error. Why does this happen when i have already inserted an argument?? is it a problem with the filter syntax?

Answer 1

You have a space after the colon which is confusing the parser. Use it like this instead:

{{ model_class|field_values:field }}

(Note that your code is pretty inefficient: it's querying the database over and over again, once for each field. Rather than doing this, you should probably query it once in the view and group the output by field.)