Logic Block Scripting

Documentation of logic block scripting concepts

For general scripting concepts refer to this page: Scripting

Rule logic script

The Rule logic script defines the custom logic that is evaluated during rule runs.

function consume(event) {
  var temperature = event.inputs.temperature;
  var threshold = event.properties.tempThreshold;

  if (temperature < threshold) {
    emit("action", {
      message: `it is too cold: the temperature is ${temperature}°C`,
    });
  }
}

Once a Custom Logic Block is saved, it can be selected as a logic block when creating a rule. Inputs need to be linked to an input device or tag and parameters need to be set.

Further, one or more actions need to be defined. The templating syntax can be used to access the results of a Custom Logic Block {{result.*}}. For example, {{result.message}} for the script shown above.

Custom logic timer

There is also the possibility to emit a timer inside the custom logic block.

When emitting the timer event, two params can be specified

• runAt required, a date which needs to be at least 15 seconds in the future

• meta optional, object which can contain any values

The meta object will be available when the rule is triggered by that timer and can be accessed at timer.meta during script run. This can provide useful information for the next timed run or help uniquely identify timers when running them.

Refer to Stateful Operations for more information on how to share data between runs of a rule.

Event Object

The Custom Logic Block script is invoked with the event object as param. It contains the following properties & strucutre:

• inputs object, contains the values of the specified variables

• state object, contains the user defined rule state

• type string, indicates how the rule was invoked (either timer or uplink)

• dataSources object, see data source properties

• device object, see device properties

• properties object, contains the user defined properties of the custom logic block

Note: if type has the value of timer certain properties will behave differently:

• the variable values of the inputs object will be null

• dataSources will be an empty object

• device will be undefined

Device Properties

The following properties of a device can be accessed when using template syntax.

Note: The prefix device. is always required in order to access sub properties.

• name the device name

• description the device description

• integrationId the integrationId of the device (only for LoRaWAN devices)

• workspaceId the workspaceId of the device

• dataFlowId the data flow id of the device

• connectivity the connectivity of the device

• id the akenza device id

• deviceId the unique device id

Data Source Properties

The following properties of a data source can be accessed when using template syntax.

To access a specific data source, use dataSources.X where X is the number of the data source as specified in the rule (starting at 1).

Some properties can be null in certain circumstances (e.g. the correlationId or the device) if e.g. the rule was triggered by a timer event or the data source is set to access the last sample.

Note: The prefix dataSources.X. is always required in order to access sub properties.

• correlationId the correlation id of the data source (only available if the data source was triggering the flow)

• device the complete device object. See Device Properties for sub properties

• deviceId the unique device id

• akenzaDeviceId the akenza device id

• topic the topic of the sample

• timestamp the timestamp of the sample

• data.* access any values of the sample.

• meta.* access any values of the meta object

• uplinkMeta the complete uplink meta object

• trigger boolean, indicates whether the data source has triggered the uplink

• deviceInput boolean, indicates if the data source is a device

• tagInput boolean, indicates if the data source is a tag

The values related to the sample (namely correlationId, topic, timestamp, data, meta and uplinkMeta) are resolved based on which data source triggered the rule evalution. If the data source is triggering (trigger = true) the rule, the values will be the one from the triggering uplink. Otherwise the values will correlate the most recent stored sample.

Uplink Meta Properties

The following properties of uplink meta data can be accessed when using template syntax

Note: The prefix uplinkMeta. is always required in order to access sub properties.

• dataReceived the ISO-8601 timestamp when the data was recieved

• bytesReceived the number of bytes received in the uplink request

• processingStart the ISO-8601 timestamp when the processing was started

• scriptRunUplinkStart the ISO-8601 timestamp when script run was started

• scriptRunUplinkEnd the ISO-8601 timestamp when script run ended

• processingEnd the ISO-8601 timestamp when the processing ended

• outputProduced the ISO-8601 timestamp when all output were produced

• uplinkDuration the ISO-8601 duration of the whole uplink flow

• processingDuration the IOS-8601 duration of the processing

• scriptRunningDuration the ISO-8601 duration of the script run

Emitting actions

If a condition is met, an action has to be emitted that will invoke the consecutive rule actions.

Re-invoking the rule engine

It is possible to re-invoke the rule engine by enabling the setting in the rule action. This is useful, to apply another rule to the output of a custom logic block.

Note that the emit action is expected to have a specific format (same structure as the sample output in device type scripts), see Emit Function for details. This means that properties like topic, timestamp (optional) and data should be provided and will be processed in subsequent rules.

If the topic is specified in the emit action, it will override the one specified in the custom akenza db rule action.

Rule Action - Custom Payload

When using a custom payload template in the rule action, make sure to use {{result.*}} to access data that has been emitted as part of the rule action. For example, to store the result of a rule action that has been used to re-invoke the rule engine, use {{result.data}}. Otherwise the whole result object will be stored as a sample meaning topic, timestamp, data and meta (if specified) will be contained in the data object.

Emitting a timer

By emitting a timer, you can schedule a rule to run be invoked again in the future.

meta can then be accessed using event.timer.meta.

Event examples

Logic Block uplink event

A decoded uplink that triggers a custom logic block, looks as follows. Note that the state is controlled by the script author (see Stateful Operations):

Logic Block timer event

A time-based event that triggers a custom logic block, looks as follows. Note that the state is controlled by the script author (see Stateful Operations):

Logic Block last sample timer event

A time-based event that triggers a custom logic block, looks as follows.

Note that the state is controlled by the script author (see Stateful Operations):