Plotly dash user dependent server side caching

Question

I'm using server side caching in my dash application and I've followed example 4 in the documentation. I'm using this to query and process the "global" data, this prepared dataset is then shared between different components in the application.

I'm trying to tweak the example such that the caching also depends and reloads on some user input.

I've tried with something like below which doesn't really make sense - what is the best approach to achieve what I'm after?

app = dash.Dash(__name__)

cache = Cache(app.server, config={
    'CACHE_TYPE': 'redis',
    'CACHE_TYPE': 'filesystem',
    'CACHE_DIR': 'cache-directory',
    'CACHE_THRESHOLD': 200
})

def get_dataframe(session_id, user_input_value):
    @cache.memoize()
    def query_and_serialize_data(session_id):
        df = # Here I make my query based on user_input_value 
             # If there is no input I just return an empty df
        return df.to_json()
    return pd.read_json(query_and_serialize_data(session_id))

def serve_layout():
    session_id = str(uuid.uuid4())

    return html.Div([
        html.Div(session_id, id='session-id', style={'display': 'none'}),
        # User input            
        # My output which doesn't behave as expected
    ])

app.layout = serve_layout

# Callback related to the user input

@app.callback(
    [
        Output('my-output', 'output-component')
    ],
    [
        Input('session-id', 'children'),
        Input('user-input', 'value')
    ]
)
def generate_output(session_id, user_input_value):
    df = get_dataframe(session_id, user_input_value)
    return # Output component

if __name__ == '__main__':
    app.run_server(debug=True)

emher emher · Accepted Answer · 2020-08-06T04:45:18

In the code you have posted, the user_input_value value never reaches the memoized function. If you change your code so that it does, i.e. pass the user_input_value to the query_and_serialize_data function, it should work as intended

def get_dataframe(session_id, user_input_value):
    @cache.memoize()
    def query_and_serialize_data(session_id, user_input_value):
        df = # Here I make my query based on user_input_value 
             # If there is no input I just return an empty df
        return df.to_json()
    return pd.read_json(query_and_serialize_data(session_id, user_input_value))

Plotly dash user dependent server side caching

1 Answers