How to dynamically/programmatically subscribe to a datasource from a ThingsBoard widget?

Question

I'm working with a ThingsBoard widget and I'm looking for a way to programmatically subscribe to a data source where the field/attribute or timeseries key is not predetermined.

Currently, I can utilize the dashboard state to subscribe to entities (assets, devices) or clients dynamically. However, this approach requires prior knowledge of the attribute name, which in my case is dynamic.

Is there a method or API within ThingsBoard that allows for such dynamic attribute subscriptions within a widget? Any examples or documentation pointers would be highly appreciated.

Answer 1

To dynamically subscribe to data sources in a ThingsBoard widget, you can utilize the createSubscriptionFromInfo method provided by the subscriptionApi. This method allows you to create subscriptions based on a configuration object that can include dynamic attributes or timeseries keys determined at runtime.

Example:

self.onInit = function() {
    // Function to dynamically determine the key
    const dynamicKey = getDynamicKeySomehow();

    // Subscription configuration for the dynamic key
    let valueSubscriptionInfo = {
        type: 'timeseries',
        entityType: 'ASSET', // or DEVICE
        entityId: '00000000-0000-0000-0000-000000000000', // Replace with UUID of your entity
        timeseries: [{
            name: dynamicKey
            // You can add more options here if necessary
        }],
        attributes: []
    };
    const subscriptionOptions = {
        callbacks: {
            onDataUpdated: (subscription, detectChanges) => {
               self.onDataUpdated(subscription, detectChanges);
            },
            onDataUpdateError: (subscription, e) => console.warn,
        }
    };

    // Create the subscription
    self.ctx.myubscription = self.ctx.subscriptionApi.createSubscriptionFromInfo('timeseries', valueSubscriptionInfo, subscriptionOptions, false, true)
            .subscribe((subscription) => {
                // You now have a subscription object you can use
            });
};

self.onDataUpdated = function(subscription, update) {
    // Handle the updated data here
};

self.onDataUpdateError = function(subscription, error) {
    // Handle any errors here
};

In this example, getDynamicKeySomehow is a function that should be implemented to determine or retrieve the dynamic key. The onDataUpdated and onDataUpdateError functions are callbacks that handle data updates and errors, respectively.

Don't forget to clean up and unsubscribe when the widget is destroyed to avoid any potential memory leaks:

self.onDestroy = function() {
    if (self.ctx.mySubscription) {
        self.ctx.mySubscription.unsubscribe();
    }
};

See related GitHub issue for more info.