Rule Logic - Custom Logic Blocks

This page describes the Custom Logic Blocks in more detail

Custom Logic Blocks allow the implementation of more complex business logic with the akenza Rule Engine. They enable simple stateless and stateful operations upon rule trigger using custom scripts in Javascript. Custom Logic Blocks are created on organization-level and are therefore available in all workspaces and can be selected when creating a rule.

This webinar explains how to create Custom Rules:

Webinar about how to create Custom Rules

A set of examples for logic blocks can be found here:

GitHub - akenza-io/akenza-logic-block-examples: A set of examples for using custom logic blocks in the akenza Rule Engine. Topics ResourcesGitHub

A Custom Logic Block consists of a definition of:

• Inputs: the dynamic data that is evaluated during script execution (sensor data)

• Parameters: constant values like thresholds

• A script used to run the logic

In order to keep its usage consistent, it is not possible to edit custom logic inputs and parameters if the Custom Logic Block is assigned to an active rule.

Inputs

Inputs specify the input data sources for a Custom Logic Block and contain the dynamic data of a device. At least one input needs to be defined in order to create a Custom Logic Block.

Field	Description
Input display/ label name	The input name
Input description	An optional description
Input variable name	A variable name used to access the value inside the script
Default topic	An optional default topic that is preselected when using the logic block
Default data key	An optional default data key that is preselected when using the logic block

Parameters

Parameters represent static properties that are available during script runtime.

Field	Description
Parameter display/label name	The parameter name
Parameter variable name	A variable name used to access the parameter inside the script
Parameter Type	The data type of the parameter; Numerical, String, or Boolean
Default value	A default value for the parameter

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.

function consume(event) { 
  let time = new Date();
  time = new Date(time.setDate(time.getDate() + 1));
  time = time.setHours(0,0,0,0);
  emit("timer", {runAt: new Date(time), meta: {"foo": "bar"}});
}

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