How to invalidate or delete a redis cache object if an error in Flask view

Question

I am facing an issue where I am using the Flask cache module and in the case I have a runtime error I don't want the view cached.

Can anyone advise how to do this?

Here is what I would like to achieve.

from flask import Flask    
from flask.ext.cache import Cache

app = Flask(__name__)
mycache = Cache()
mycache.init_app(app)

@mycache.cached()
@app.route('/myview')
def process_view():
    try:
        return get_something()
    except:
        return print_error_and_no_cache_this_view()

Any thoughts on how I stop this view being cached if I have an error?

score 2 · Accepted Answer · edited May 09 '18 at 12:20

You can call cache.delete_memoized in an after_this_request handler:

# @cached needs to be invoked before @route
# because @route registers the handler with Flask
# and @cached returns a different function.
# If you @route first and then @cache Flask will
# always execute the *uncached* version.

@app.route('/myview')
@mycache.cached()
def process_view():
    try:
        return get_something()
    except:

        @app.after_this_request
        def clear_cache(response):
            mycache.delete_memoized('process_view')
            return response

        return print_error_and_no_cache_this_view()

Alternately, looking at the code for Flask-Cache it appears it does not handle errors thrown by the view. So you could simply raise the error yourself and handle the exception with a separate handler:

@app.route('/myview')
@mycache.cached()
def process_view():
    try:
        return get_something()
    except Exception as e:
        raise ProcessViewIssue(e)

@app.errorhandler(ProcessViewIssue)
def handle_process_view_error(e):
    return print_error()

What do you mean in the comment about \@cached needs to come before \@route but then in your example they are the other way around? — Andrew, Apr 25 '14 at 11:29
@Andrew - sorry, what I meant was that `@cached` needs to come before `@route` in the *execution* order, not source order. Decorators are executed inmost to outermost, so the one closest to the function is executed, then the one above that, then the one above that, and so on. Basically, you want to ensure that your code is doing this: `process_view = app.route(mycache.cached(process_view -> code))` rather than `process_view = mycache.cached(app.route(process_view -> code))` — Sean Vieira, Apr 25 '14 at 15:08

How to invalidate or delete a redis cache object if an error in Flask view

1 Answers1