Callback on page refresh

Dash Python
1

This is probably simple, but how can I get a callback to run when someone refreshes the page?

I had a previous app that once it was deployed on Docker wouldn’t refresh the current date until I put the function as a callback with dcc.Interval. Prior to dcc.Interval, it was only showing the current date when the container was built.

Now I’m working on a new app and we are hoping that we can run the SQL query only when someone opens the app or refreshes the page. Thoughts on this?

2

Hello @bpolasek,

You can do this by having the query associated with the layout as a function, upon the layout rendering, the query will rerun.

def layout():
     df = getData() # this is your query function
     return yourLayout with df

Now, if you are trying to have the query be stored for multiple people, say it is a costly query, you could have the above query run from a cache of the table and have a time interval that would update the cache accordingly.

3

Okay that makes sense. However I’m having trouble figuring out where it goes. I can’t put it in the div at the top because it throws an error so where would it go? I haven’t used the layout as a function yet so this is unfamiliar to me.

nav = navbar.navbar()
side = sidebar.sidebar_component()
spot = spotlight.spotlight_component()


def serve_layout():
    layout = html.Div([
        nav,
        dbc.Container([
            dbc.Row([
                dbc.Col([
                    # sidebar
                    html.Div(
                        side,
                        id='sidebar'
                    )
                ],
                    width=2
                ),
                dbc.Col([
                    # main area
                    dbc.Row([
                        spot,
                        spot,
                        spot,
                        spot
                    ],
                        style={'display': 'flex', 'justify-content': 'space-around', 'margin-top': '70px'}
                    ),
                    dbc.Row([
                        dcc.Graph(
                            figure={}
                        )
                    ]),
                    dbc.Row([
                        # data table
                    ])
                ],
                    width=10
                )
            ],
                className='g-0'
            ),
        ],
            fluid=True,
            style={'margin-left': '0px'},
        )
    ])

 return layout


app.layout = serve_layout
5

Okay maybe I got it. I put it in the table. This should allow it to auto-update on page refresh?

nav = navbar.navbar()
side = sidebar.sidebar_component()
spot = spotlight.spotlight_component()
df = pod.get_water_chem_data()


def serve_layout():
    layout = html.Div([
        # df,
        nav,
        dbc.Container([
            dbc.Row([
                dbc.Col([
                    # sidebar
                    html.Div(
                        side,
                        id='sidebar'
                    )
                ],
                    width=2
                ),
                dbc.Col([
                    # main area
                    dbc.Row([
                        spot,
                        spot,
                        spot,
                        spot
                    ],
                        style={'display': 'flex', 'justify-content': 'space-around', 'margin-top': '70px'}
                    ),
                    dbc.Row([
                        dcc.Graph(
                            figure={}
                        )
                    ]),
                    dbc.Row([
                        dash_table.DataTable(df.to_dict('records'), [{'name': i, 'id': i} for i in df.columns])
                    ])
                ],
                    width=10
                )
            ],
                className='g-0'
            ),
        ],
            fluid=True,
            style={'margin-left': '0px'},
        )
    ])

    return layout

app.layout = serve_layout
6

You’ll need to requery the info (df) inside of the function as well. :slight_smile:

Have it outside of the layout =.

7

Ah yes makes sense. Thank you!

1 Like