Django + decorators: Adding context to the template based on a criteria.

Question

Hi there,

I'm not sure if decorators are the best way to do this, but I've removed the idea of using context processors and I'm not sure if a middleware is what I'd like.

My situation is as follows: We process sales and other data daily. Every month, we close the month off just like any other business. We do this on paper, but I would like to apply the same thing to our system. So basically, make data read-only if it falls within the closed off date.

I've easily figured out how to do this on the processing/backend side, but how would I pass such a context to a template without editing a ton of my view functions? I simply want to pass a decorator to my functions that will test the date of the instance that's being passed and add some context to the template so I can display a little message, letting the user know why the "Save" button is blanked out.

I hope my question makes sense. Thanks in advance.

Answer 1

I would use a custom template tag. It makes it very easy to set context variables

#yourapp/templatetags/business_tags.py

from django import template
register = template.Library()

class BusinessNode(template.Node):
  def __init__(self, instance, varName):
    self.instance, self.varName=instance, varName

  def render(self, context):
    instance=template.Variable(self.instance).render(context)
    if instance.passes_some_test():
      context[self.varName]='Some message'
    else:
      context[self.varName]="Some other message"
    return ''
@register.tag
def business_check(parser, token):
  bits=token.split_contents()
  if len(bits)==5:
    return BusinessNode(bits[2],bits[4])
  return ''

Then in your template

{% load business_tags %}

{% business_check for someVar as myMessage %}
{{myMessage}}

This works equally well for inserting other types of data into the context.