Question

Here’s another question about Django.

I have this code:

views.py

cursor = connections['cdr'].cursor()
calls = cursor.execute("SELECT * FROM cdr where calldate > '%s'" %(start_date))
result = [SQLRow(cursor, r) for r in cursor.fetchall()]
return render_to_response("cdr_user.html",
    {'calls':result }, context_instance=RequestContext(request))

I use a MySQL query like that because the database is not part of a django project.

My cdr table has a field called duration, I need to divide that by 60 and multiply the result by a float number like 0.16.

Is there a way to multiply this values using the template tags? If not, is there a good way to do it in my views?

My template is like this:

{% for call in calls %}
    <tr class="{% cycle 'odd' 'even' %}"><h3>
        <td valign="middle" align="center"><h3>{{ call.calldate }}</h3></td>
        <td valign="middle" align="center"><h3>{{ call.disposition }}</h3></td>
        <td valign="middle" align="center"><h3>{{ call.dst }}</h3></td>
        <td valign="middle" align="center"><h3>{{ call.billsec }}</h3></td>
        <td valign="middle" align="center">{{ (call.billsec/60)*0.16 }}</td></h3>
    </tr>
{% endfor %}

The last is where I need to show the value, I know the “(call.billsec/60)*0.16” is impossible to be done there. I wrote it just to represent what I need to show.

Answer 1

You can do it on three different layers:

• Database level. SQL is a powerful language capable of mathematics. You could write your equation in the select part of your query. In your case, that should be along the lines SELECT (duration/60*0.16) FROM cdr;. Examples can be found here and on Google. Note that in this case, stress (algorithm complexity) is put on the MySQL server process and not the Python process.
• View level. In your example, just before your return, you could loop over every element of your result variable to modify its value. You can follow the example that was given by Lie Ryan for this level.
• Template level. This is done by a custom filter. You can write your custom filter as written in the documentation and pipe your template variable through this filter in order to get the desired value.

Something along these lines would represent a custom filter applicable on your template(s):

@register.filter
def customFilter(value):
    return value / 60.0 * 0.16

You would then use it this way in your template, after {% load %}-ing the custom filter (read the documentation for more implementation information):

{{ billsec|customFilter }}