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Real-Time data fetch in the REST API

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Use case

When building an embedded analytics application, you’d like to provide a real-time experience to the users. On some page, you’d like to display a chart that updates as soon as the data changes in the database.

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Configuration

When using the REST API, you can use the WebSocket transport to receive real-time updates. Using this transport enables subscriptions to real-time updates.

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Client code

JavaScript example: 
import cube from "@cubejs-client/core";
import WebSocketTransport from "@cubejs-client/ws-transport";

const cubeApi = cube({
  transport: new WebSocketTransport({
    authorization: CUBE_TOKEN,
    apiUrl: "ws://localhost:4000/",
  }),
});

// Create a subscription
const subscription = cubeApi.subscribe(
  {
    measures: ["logs.count"],
    timeDimensions: [
      {
        dimension: "logs.time",
        granularity: "hour",
        dateRange: "last 1440 minutes",
      },
    ],
  },
  options,
  (error, resultSet) => {
    if (!error) {
      // handle the update
    }
  }
);

// Later on, unsubscribe from subscription
subscription.unsubscribe();
React example: 
import { useCubeQuery } from "@cubejs-client/react";

const Chart = ({ query }) => {
  const { resultSet, error, isLoading } = useCubeQuery(query, {
    // The component will automatically unsubscribe when unmounted
    subscribe: true,
  });

  if (isLoading) {
    return <div>Loading...</div>;
  }

  if (error) {
    return <pre>{error.toString()}</pre>;
  }

  if (!resultSet) {
    return null;
  }

  return <LineChart resultSet={resultSet} />;
};

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Refresh rate

Real-time data fetch obeys the refresh_key. In order to provide a desired refresh rate, refresh_key should reflect the rate of change of the underlying data set; the querying time should also be much less than the desired refresh rate. Please use the every parameter to adjust the refresh interval.