SolarNode DataSource Expressions

SolarNode Data Source Expressions

Many Data Source plugins for SolarNode support a general expressions framework that can be used to derive property values out of the raw values captured from the device the data source captures data from. In the SolarNode UI a typical data source might present a configurable list of expression settings like this:

In this example screen shot, each time the data source captures data from the device it is communicating with it will derive a new watts property by multiplying the captured amps and volts properties. In essence the expression is like this code:

watts = amps × volts

Expression root object

When the expression is evaluated, it is evaluated against a so-called root object. The root object is what holds the captured property values and allows the expression to refer to them.

A basic data source will provide a root object which has the following properties available to expressions:

Property	Type	Description
datum	GeneralNodeDatum	A GeneralNodeDatum object, populated with the property values read from the device.
props	Map<String,Object>	Simple map based access to all properties in datum, to simplify expressions.

Expression examples

Let's assume a captured datum like this, expressed as JSON:

{
	"i" : {
		"amps" 		: 4.2,
		"volts" 	: 240.0, 
	},
	"a" : {
		"reading" 	: 38009138
	},
	"s" : {
		"state" 	: "Ok"
	}
}

Then here are some example SpEL expressions and the results they would produce:

Expression	Result	Comment
datum.s['status]	Ok	Returns the state status property directly, which is Ok.
props['status']	Ok	Same result as datum.s['status'] but using the short-cut props accessor.
props['amps'] * props['volts']	1008.0	Returns the result of multiplying the amps and volts properties together: 4.2 × 240.0 = 1008.0.