Modify attribute on device by IOT-Agent Json - fiware

Question

I am using IOT-agent JSON with MQTT binding
I have a sensor-actuator registered in orion using iot-agent and I created the subscription.
If a third party application modifies a sensor value, orion must send iot-agent information and iot-agent to the device.
for example, if I have 3 attributes inside the sensor and one of them controls a valve.
In orion that attribute is true or false.
if the attribute is modified in orion must be sent to iot-agent and iot-agent to the device to close or open the valve.
extra information:
The software is two component of Fiware Generic Enable.
iot-agent JSON: https://github.com/telefonicaid/iotagent-json
Fiware-orionCB: https://github.com/telefonicaid/fiware-orion
Is it possible?

Answer 1

There is no official tutorial connecting the JSON IoT Agent to a device over MQTT, but a very similar one exists for the Ultralight IoT Agent
IoT Devices are either:
sensors - reading measurements from the real world
actuators - altering the state of the world
or both
Your issue here is that you cannot get Orion to update the attribute/state of a sensor directly. The attributes of the entity in the Context Broker represent the incoming state of the sensor - i.e. the measurements from that sensor.
For example for the sensor reading the state of a valve it could be "open: "true"
In order to update an actuator, you will need to send a command, rather than alter the value.
You should set up the command when provisioning the device (it is assumed you have a service already):
curl -iX POST \
'http://localhost:4041/iot/devices' \
-H 'Content-Type: application/json' \
-H 'fiware-service: openiot' \
-H 'fiware-servicepath: /' \
-d '{
"devices": [
{
"device_id": "bell001",
"entity_name": "urn:ngsi-ld:Bell:001",
"entity_type": "Bell",
"protocol": "PDI-IoTA-UltraLight",
"transport": "MQTT",
"commands": [
{ "name": "ring", "type": "command" }
],
"static_attributes": [
{"name":"refStore", "type": "Relationship","value": "urn:ngsi-ld:Store:001"}
]
}
]
}
'
You can then send the command to do something (like ring a bell, open a valve etc.) by altering the state of the command attribute.
curl -iX PATCH \
'http://localhost:1026/v2/entities/urn:ngsi-ld:Bell:001/attrs' \
-H 'Content-Type: application/json' \
-H 'fiware-service: openiot' \
-H 'fiware-servicepath: /' \
-d '{
"ring": {
"type" : "command",
"value" : ""
}
}'
Depending upon how you have provisioned devices, you may also need to register the command - though this may not be necessary.