Reply to RPC call with related device telemetry

This recipe shows how to handle a client-side RPC call from a device by fetching telemetry from a related device and returning it as the RPC response.

A Controller sends a client-side RPC call with method getCurrentTemperature.

ThingsBoard:

• routes the request to a dedicated rule chain
• fetches the latest temperature from a related Thermostat device
• returns the temperature value as the RPC response

Devices

• Thermostat A with type thermostat
• Controller A with type controller

Relation

• Controller A -- Thermostat --> Thermostat A

Rule chains

• modified Root Rule Chain
• new Related thermostat temperature rule chain

Create two devices:

Device 1

• Name: Thermostat A
• Type: thermostat

Device 2

• Name: Controller A
• Type: controller

Create a relation:

• From: Controller A
• To: Thermostat A
• Relation type: Uses

You can import a ready-made rule chain or build it manually.

Option 1. Import rule chain

• Download the Related Thermostat Temperature rule chain as a JSON file and import it into your instance.

Option 2. Create manually

• Create a new rule chain named Related Thermostat Temperature, open it, and add the following nodes:

Add the Related Entity Data node and connect it to the Input node.

This node fetches the latest temperature from Thermostat A and saves it in message metadata as roomTemperature.

Fill in the fields:

• Name: Get Temperature from Related Thermostat
• Direction: From originator
• Max relation level: 1
• Relation filters:
  • Relation type: Uses
  • Entity type: Device
• Data to fetch: Latest telemetry
• Latest telemetry mapping:
  • Source attribute key: temperature
  • Target key: roomTemperature

Configure the Related Entity Data node to fetch data from related devices using the Uses relation. Set direction to From originator and limit the relation level to 1. Map the related device telemetry key temperature to roomTemperature and store it in metadata for further processing in the rule chain.

Add the Transformation Script node and connect it to the Related Entity Data node with relation type Success.

This node builds the RPC reply payload. The RPC call reply node sends the message payload as the response, so the payload must contain the temperature value.

Fill in the fields:

• Name: Build Response

Script:

return {msg: {temperature: metadata.roomTemperature}, metadata: metadata, msgType: msgType};

return {msg: {temperature: metadata.roomTemperature}, metadata: metadata, msgType: msgType};

Add the RPC call reply node and connect it to the Transformation Script node with relation type Success.

This node reads requestId from message metadata and sends the message payload as the RPC response to the originator.

Fill in the fields:

• Name: Send Response
• Request ID: requestId

• Input ⇾ Get Temperature from Related Thermostat
• Get Temperature from Related Thermostat ⇾ Success ⇾ Build Response
• Build Response ⇾ Success ⇾ Send Response

Save the rule chain.

Open the Root Rule Chain. By default, the Message Type Switch node routes RPC Request from Device messages to a Log node named Log RPC from Device.

Add the following nodes after Message Type Switch:

Add the Filter Script node and connect it to the Message Type Switch node with relation type RPC Request from Device, replacing the existing connection to Log RPC from Device.

This node passes only requests with method getCurrentTemperature.

Fill in the fields:

• Name: Filter getCurrentTemperature RPC

Script:

return msg.method == 'getCurrentTemperature';

return msg.method == 'getCurrentTemperature';

Add the Rule Chain node and connect it to the Filter Script node with relation type True.

This node forwards matched requests to the Related thermostat temperature rule chain.

Fill in the fields:

• Name: To Related Thermostat Temperature
• Rule Chain: Related Thermostat Temperature

Connect the existing Log RPC from Device node to the Filter Script node with relation type False.

Requests with an unrecognized method are logged instead of dropped.

• Message Type Switch → RPC Request from Device → Filter getCurrentTemperature RPC
• Filter getCurrentTemperature RPC → True → To Related thermostat temperature
• Filter getCurrentTemperature RPC → False → Log RPC from Device

Save the Root Rule Chain.

1. Publish temperature telemetry for Thermostat A. Go to the device Check connectivity tab, copy the curl command and execute it, or run:

   curl -v -X POST -d '{"temperature":25}' https://$THINGSBOARD_HOST/api/v1/$ACCESS_TOKEN/telemetry --header "Content-Type:application/json"

   Replace $ACCESS_TOKEN with the access token of Thermostat A.

   

2. Send an RPC request from Controller A. Go to the device Check connectivity tab and copy the curl command. Replace telemetry with rpc in the URL and use this payload:

   curl -v -X POST -d '{"method":"getCurrentTemperature","params":{}}' https://$THINGSBOARD_HOST/api/v1/$ACCESS_TOKEN/rpc --header "Content-Type:application/json"

   

   Replace $ACCESS_TOKEN with the access token of Controller A.

Expected result:

The response contains the temperature reported by Thermostat A:

{"temperature":"25"}

If an RPC call with an unknown method is sent, the Log RPC from Device node logs the request:

Incoming message:

{ "method": "getCurrentHumidity", "params": {} }

Incoming metadata:

{ "deviceName": "Controller A", "deviceType": "controller", "requestId": "0", "serviceId": "tb-http-transport-1", "sessionId": "68587996-a91b-4095-9c1a-5c6aa3f02183" }

Verify the Debug events for the Log RPC from Device node to inspect incoming RPC requests with unsupported methods. Review the RPC request payload to confirm the unsupported method (e.g., getCurrentHumidity) received by the platform. Inspect the metadata associated with the RPC request, including requestId, serviceId, and sessionId.

• RPC capabilities — for more information about how RPC works in ThingsBoard.
• Trigger related entities via relation — a related recipe using relations to trigger actions on another device.
• Related Entity Data node — node reference for fetching data from related entities.