Historical data

Using datalinks, any widget can expose its properties to other widgets. By reimplementing the readHistData method of BaseWgt, a widget can also provide access to the historical data of its properties.

TagMgr is the standard widget for attaching device data via device slots, abstracting away direct API calls.

Additionally, data source widgets can provide access to historical data through other mechanisms. For example, the platform offers DatasourceWgt for advanced aggregation queries and DatasourceGraphQLWgt for accessing GraphQL APIs.

Widgets that support historical data views can use the Datalink::fetchHistoricalData method as a convenient way to retrieve historical data for their linked properties, regardless of the data source.

The SDK example demonstrates how to:

• Expose a property that can be linked to a model property using a datalink.
• Fetch historical data whenever the time interval changes.

To achieve this, it:

• Overrides BaseGraphicWgt::addDatalink to obtain a reference to the source widget and property.
• Overrides BaseGraphicWgt::setPropertyValue to trigger data fetching whenever the time interval changes.
• Defines a fetch method to retrieve historical data through the datalink using readHistData.

BaseGraphic Methods

BaseGraphicWgt::addDatalink

The method addDatalink is called every time a datalink is added to the widget.

BaseGraphicWgt::setPropertyValue

The method setPropertyValue is called every time a widget property is changed.

Example

  // Override BaseGraphicWgt::addDatalink
  public addDatalink( dataLink: IDataLinkConstructorArgs )
  {
    const newDatalink = super.addDatalink(dataLink);
    switch( dataLink.tgtProp )
    {
      case "tagReference":
        this.sourceDatalink = newDatalink;
        break;
    }
    return newDatalink;
  }

  // Override BaseGraphicWgt::setPropertyValue
  public setPropertyValue( { prop, value } )
  {
      super.setPropertyValue( { prop, value } );
      switch ( prop )
      {
        case "from":
        case "to":
          this.fetchData();
          break;
      }
  }

  // Example methods to get historical data from cloud
  private async fetch( from: number, to: number ): Promise<DataValue[]>
  {
    if ( !this.dataSource || !this.tagName )
      return [];

    // Here and example to request 
    const data = await this.sourceDatalink.fetchHistoricalData({
        from,         // Start date in milliseconds
        to,           // End date in milliseconds
    });
    return data;
  }