django template system, calling a function inside a model

I want to call a function from my model at a template such as:

class ChannelStatus(models.Model):
 ..............................
 ..............................

    def get_related_deltas(self,epk):
        mystring = ""
        if not self.get_error_code_delta(epk):
            return mystring
        else:
            for i in self.get_listof_outage():
                item = i.error_code.all()
                for x in item:
                    if epk == x.id:
                        mystring= mystring +" "+str(i.delta())
        return mystring         

And when I want to call this from the template: assume while rendering, I pass channel_status_list as

channel_status_list = ChannelStatus.objects.all()

{% for i in channel_status_list %}
  {{ i.get_related_deltas(3) }}
{% endfor %}

This doesn't work, I am able to call a function that consumes nothing, but couln't find what to do if it has parameter(s)

Cheers

Solution 1:

You can't call a function with parameters from the template. You can only do this in the view. Alternatively you could write a custom template filter, which might look like this:

@register.filter
def related_deltas(obj, epk):
    return obj.get_related_deltas(epk)

So now you can do this in the template:

{% for i in channel_status_list %}
  {{ i|related_deltas:3 }}
{% endfor %}

Solution 2:

If the method doesn't require any arguments, you can use the @property decorator and access it normally in the template.

class ChannelStatus(models.Model):
    ...
    @property
    def function_you_want_as_property(self):
        mystring = ""
        ...

Solution 3:

For > 1 argument, use simple tags:

@register.simple_tag
def related_deltas(obj, epk, second_arg):
    return obj.get_related_deltas(epk, second_arg)

Template:

{% for i in channel_status_list %}
  {% related_deltas i 3 4 %}
{% endfor %}

(Note the change of syntax from {{ to {%)

Can take positional parameters (e.g. related_deltas i 3 second_arg=4 debug=true).

Solution 4:

If you find that there are too many properties running around everywhere or you have a template filter for every other method that you write, another solution was suggested on IRC thanks @FunkyBob. It's a little well, erm, funky but it is nice in certain cases.

  class MethodProxy(object):
        """For consolidating into 1 method the calling of methods with various single args
        (suitable dictionary keys)

        class MyModel(models.Model):
            ...

            def magic(self, value):
                # Free the ponies

            def thing(self):
                return MethodProxy(self.magic)

        # Usage
        >>> m = MyModel()
        ...
        >>> m.thing['value'] == m.magic('value')

        # template
        {{ m.thing.value }}

        """

        def __init__(self, method):
            self.method = method
        def __getitem__(self, key):
            return self.method(key)