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?

Answer 1

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()