Binding Examples

This section offers some real-life examples of dashboard bindings.

This binding will make a status panel red if a voltage alert is reported by the controller. In other cases the panel will be green.

Note that the expression and the target reference use relative context paths (".") to make the dashboard compatible with multiple similar controllers. The dashboard should be relative and valid for all "voltage controller" devices.

It's possible to modify the above binding to make the panel red if temperature reading is over 50 degrees: ({.:voltage$voltage} > 50) ? "background-color: red" : "background-color: green"

This pair of bindings will change setpoint of a controller (e.g. temperature controller) once a number field component changes its value.

First binding is used to read current setpoint value from the controller and initialize the number field:

Second binding writes new setpoint to the controller once the slider is moved:

This binding executes a server query whose text is contained in the text field queryText and puts query results into the Data Table Editor component named results.

The query is executed by calling executeQuery of the root server context. The operation is performed upon execute button click.

Note that first parameter of executeQuery function is single-quoted to make the system processing it as expression.

It's possible to use alternative syntax for the above binding's expression: callFunction("", "executeQuery", {form/queryText:text}) This expression works exactly as the above one. However, it uses callFunction() expression language function to call the server context function by explicitly specifying context path, function name and its parameters.

This example explains how to perform device or server function call from a dashboard. Assuming we have a device supporting multiply operation with two numeric arguments. We'd like to call this operation upon calculate button click by supplying numbers entered in two text fields (argument1 and argument2).

In this case our binding's target will point to the function and its expression will return a pre-build parameters data table:

Note that we're using relative context path (".") in the target to make calculation dashboard compatible with many calculation agents. To use it with just one agent, specify absolute path, e.g. users.my_user.devices.my_agent.

In this example calculation result returned by multiply operation will be discarded. But what if we want to put it into another dashboard component (such as a label)? Here is the solution:

In this case our binding expression will call the function and return its output (a Data Table). The actual calculation result (numeric result field) is extracted from this table using cell() function. This result is written into result label:

Note that relative device context path (returned by dc() function) is used. To use absolute context path change dc() to full device path, e.g. users.my_user.devices.my_agent.

There is another (more compact) style of writing the above binding expression to obtain exactly the same result. This style uses a function reference instead of callFunction() expression language function: {.:multiply('{form/argument1:text}', '{form/argument2:text}')$result}

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