Live-update from Postgres database callback

Dash Python
1

I’m attempting to create a live-update dashboard that connects to a Postgres DB on AWS. I’ve made a function that connects to the database, I initiated a connection and mapped the database. In the callback I’ve called the function. On initial load up, I get the data and it works well, however, when I update the database, the callback doesn’t update the new data. I’m not sure where my error in reasoning is, if anyone could give me a pointer. I’ve made an abbreviated example of my code below. Thanks

import plotly.graph_objs as go
import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output, State
from plotly.subplots import make_subplots
from sqlalchemy import create_engine, MetaData, Table
from sqlalchemy.ext.automap import automap_base
from sqlalchemy.orm import declarative_base
from sqlalchemy import Column, Integer, String, func, Date, ARRAY
from sqlalchemy.orm import sessionmaker

app = dash.Dash(__name__, external_stylesheets=[BS], suppress_callback_exceptions=True, update_title=None)
server=app.server


class DbConnection:
    def __init__(self, **kwargs):
        self.DB_URI = os.environ.get('DB_URI', kwargs.get('DB_URI'))
        # self.DB_URI = aws_parameter['Parameter']['Value']
        self.echo = kwargs.get('echo', True)
        self.future = kwargs.get('future', True)
        # Now create the engine
        self.engine = create_engine(self.DB_URI, echo=self.echo, future=self.future)
        # Make the session maker
        self.session_maker = sessionmaker(bind=self.engine)

    @property
    def session(self):
        """Return a session as a property"""
        return self.session_maker()

 # instantiate the database connection and map your base
my_db_connection = DbConnection()  # provide kwargs as needed
session = my_db_connection.session  # necessary to assign property to a variable

# Map the classes
Base = automap_base()
Base.prepare(my_db_connection.engine, reflect=True)
User = Base.classes.users
Datex = Base.classes.data

@lru_cache()
def get_blood_pressure(session, user_id, date):
     blood_pressure, time = [], [], 
    query = session.query(Datex) \
        .filter(Datex.user_id == user_id) \
        .filter(Datex.date_time == date)

    for instance in query:
        blood_pressure.append([instance.systolic, instance.mean, instance.diastolic])
        time.append(instance.time)
       
    return blood_pressure, time, 

app.layout = html.Div([
dcc.Store(id='time', storage_type='session'),
dcc.Store(id='blood_pressure', storage_type='session'),

html.Div(dcc.Graph(id='live-graph', animate=False), className='w-100'),
        html.Div(id= "testing"),
        dcc.Interval(
            id='graph-update-BP',
            interval=30000,
            n_intervals=0
        )]), width={"size": 10, "offset": 0.5}),
@app.callback(
    dash.dependencies.Output('live-graph', 'figure'),
    dash.dependencies.Output('blood_pressure', 'data'),
    dash.dependencies.Output('time', 'data'),
    [dash.dependencies.Input('graph-update-BP', 'n_intervals')],
)
def update_graph_scatter_1(n):
   
            trace = []
            blood_pressure = []
            time = []
           

           blood_pressure, time = get_blood_pressure(session=session, user_id=3, date='Monday,Apr:26')
     
               
            for i in range(0, len(blood_pressure)):
                trace.append(go.Box(y=blood_pressure[i],
                                    x=time[i],
                                    line=dict(color='#6a92ff'),
                                    hoverinfo='all'))
           
            fig = make_subplots(rows=1, cols=1)

            def append_trace():

                for i in range(0, len(trace)):
                    fig.append_trace(trace[i], 1, 1)

                
            append_trace()

          
            return fig, blood_pressure, time,
2

I’m with you. I have the same problem and I can’t update the charts and tables unless I restart the service.

3

In my case, the problem was solved once I removed the @lru_cache()