Stateful Operations

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Stateful Operations
Sharing data between rule runs
Alongside user-defined inputs and parameters for Custom Logic Blocks, the implicit event property called state is provided. Using the state allows users to persist and share data between different rule runs ("memory"). This can be achieved by the emitting state which will be accessible in the next rule run. The state property is shared only between runs of the same rule, regardless of the source that triggered a rule execution.
Accessing the rule state property from a Custom Logic Block script: 
function consume(event) { 
    var ruleState = event.state || {};
    //your implementation goes here...
}
 Initially event.state property is an empty object!
An example of updating a rule state property from Custom Logic Block script:
function consume(event) { 
    var ruleState = event.state || {};
    //your implementation goes here...
    ruleState["numOfSamples"] = numOfSamples;
    emit('state', ruleState);
}
or
function consume(event) { 
    //your implementation goes here...
    emit('state', { "numOfSamples":  numOfSamples });
}
An example of a Custom Logic Block script that makes use of the state property:
function consume(event) { 
    var temperature = event.inputs["temp1"]; 
    var threshold = event.properties["tempT"]; 
    var ruleState = event.state;
    if (temperature > threshold) {
        var numOfSamples = ruleState.numOfSamples;
        if (typeof numOfSamples !== "undefined") {
            numOfSamples = numOfSamples + 1;
        } else {
            numOfSamples = 1;
        }
        emit('state', { "numOfSamples":  numOfSamples });
        //Emitting action when numOfSamples is an even number
        if (numOfSamples % 2 === 0) {
            emit('action', { "message": "Rule has triggered the action!", "addedTemp": threshold + temperature }); 
        }
    } 
}
The rule state will be reset on rule deactivation or deletion. Once a rule is activated again, the rule state property will be set to a default value.
A more advanced example of using rule state:
// rule that adaptively changes the threshold based on the average temperature
function consume(event) {
  const alpha = 0.2;
  const initialThreshold = event.properties.initialThreshold;
  const currentTemperature = event.inputs.temperature;
​
  let state = event.state || {};
  let movingAverage = state.movingAverage || 0;
  let threshold = state.threshold || initialThreshold;
​
  let numberOfSamples = state.numberOfSamples || 0;
​
  //compute a moving average
  movingAverage =
    (currentTemperature + numberOfSamples * movingAverage) /
    (numberOfSamples + 1);
​
  // let's define the threshold by 20% above the average
  const currentThreshold = movingAverage * 1.2;
​
  // exponentially smooth the threshold in order to account
  // for the phase where not much data is present
  threshold = alpha * currentThreshold + (1 - alpha) * threshold;
  if (currentTemperature > threshold) {
    emit("action", {
      message: `temperature (${currentTemperature}°C) is above threshold (${threshold})`,
    });
  }
​
  numberOfSamples += 1;
  state = { threshold, numberOfSamples, movingAverage };
  emit("state", state);
}
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
​
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