Handling {null} in Mako?

[Han Chuang]

Hello,

I'm starting out with Mako, I've been working on a project that makes query to a local sqlite db and passes the results into a mako template to be drawn with javascript (Extjs)

def myView(request):
    response = request.db.execute("select * from myTable);
    results = [dict(name=row[0], id=row[1], start=row[2], end=row[3]) for row in response.fetchall()]
    return dict(results=results)

The results are passed into a template and handled, being passed into a javascript function to draw the results.

% if results
    <h2>RESULTS FOUND</h2>
    % for result in results:
        <script>
        myFunction(${result['name']}, ${result['id']}, ${result['start']}, ${result['end']});
        </script>
    % endfor
% else
    <h2>RESULTS LOST</h2>
% endif

However, the dbs I will be using have unexpected {null} items (in this case, end can be null, as can start.) Passing a none to a javascript method seems to break it and not execute it at all. How can I handle nulls in mako?

One method I've found so far is to create an if else statement for each field that can be null, then doing
% if result['name']:
    <Do the method that has it>
% else
    <Do a separate method that doesn't have it>
% endif

But this results in a lot of duplicated code and seems to be inefficient.

Summary: How can I change a None in mako to a null for javascript?

Thank you in advance!

[Benjamin Trofatter]

You could just write a filter that replaces "None" with "null in the output.

# in myfilters.py

def null_if_None(value):

    if value in (None, "None"):

        return "null"

    return unicode(value)

Then you could use this in your templates like so:

% if results
    <h2>RESULTS FOUND</h2>
    % for result in results:
        <script>

        myFunction(${result['name']}, ${result['id']}, ${result['start'] | null_if_None}, ${result['end'] | null_if_None});

        </script>
    % endfor
% else
    <h2>RESULTS LOST</h2>
% endif

And pass the import=["from myfilters import null_if_None"] as a keyword argument to your template renderer.

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