Historical data

Datalinks are used also to get historical data. In this example we will see how to get historical data from them.

The example shows how to:

• expose a property that can be linked to a model property with Datalink
• every time the time interval changes fetch historical data

To do this we will:

• override BaseGraphicWgt::addDatalink to get the reference to the source widget and the source property
• override of BaseGraphicWgt::setPropertyValue to trigger the data fetching every time the time interval changes
• define the method fetch to get historical data using the api 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.dataSource = newDatalink.getDataSourceWidget();
        this.tagName = dataLink.srcProp;
        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 =  <DataValue[]>await this.dataSource.readHistData(
        this.tagName, // Name of the tag to read
        from,         // Start date in milliseconds
        to,           // End date in milliseconds
        undefined,    // Number of samples if not defined get all samples
        false,        // apply downsampling
        undefined,    // Instead of undefined you can request to the server to perform an
                      // operation of aggreagation
                      // {
                      //   type: "average",
                      //   sampling: {
                      //     extent: 5,
                      //     size: 2,
                      //     unit: "minutes"
                      //   }
                      // }
        undefined,    // specify downsampling size
    );
    return data;
  }