Events and actions in Fiware NGSI entities - fiware

Question

Let assume we have an entity corresponding to an IoT controller device, let say a door controller.
We want to define an event that could cause an action (open/close). So we need to send a command to this device.
How would we make this happen? Add an attribute in the entity like for example setDoorStatus that can be written to via the NGSI API? And then have some IoT agent or command handler subscribe to this attribute?
Is there any example of a Data Model where this is done?

Answer 1

The easiest way to do this is to provision a device using any IoT Agent. IoT Agents have a standard API for device provisioning, where commands can be listed:
curl -L -X POST 'http://localhost:4041/iot/devices' \
-H 'fiware-service: openiot' \
-H 'fiware-servicepath: /' \
-H 'Content-Type: application/json' \
--data-raw '{
"devices": [
{
"device_id": "door001",
"entity_name": "urn:ngsi-ld:Door:001",
"entity_type": "Door",
"protocol": "PDI-IoTA-UltraLight",
"transport": "HTTP",
"endpoint": "http://context-provider:3001/iot/door001",
"commands": [
{"name": "unlock","type": "command"},
{"name": "open","type": "command"},
{"name": "close","type": "command"},
{"name": "lock","type": "command"}
],
"attributes": [
{"object_id": "s", "name": "state", "type":"Text"}
],
"static_attributes": [
{"name":"refStore", "type": "Relationship","value": "urn:ngsi-ld:Store:001"}
]
}
]
}
'
The IoT Agent node library defines a command paradigm for actuating devices through commands
In this case you have an attribute open which is registered on a context broker as coming from a device and you can actuate the device using the following request:
NGSI-v2
curl -L -X PATCH 'http://localhost:1026/v2/entities/urn:ngsi-ld:Door:001/attrs' \
-H 'fiware-service: openiot' \
-H 'fiware-servicepath: /' \
-H 'Content-Type: application/json' \
--data-raw '{
"open": {
"type" : "command",
"value" : ""
}
}'
NSGI-LD
curl -L -X PATCH 'http://localhost:4041/ngsi-ld/v1/entities/urn:ngsi-ld:Device:door001/attrs/open' \
-H 'NGSILD-Tenant: openiot' \
-H 'NGSILD-Path: /' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
--data-raw '{
"type": "Property",
"value": ""
}'
The relevant IoT Agent accepts the request and passes it down to the device using the appropriate device syntax. Once activated, additional special status and info attributes are added to the entity as soon as it has any information of the command progress.
Full examples can be found within the FIWARE Tutorials:
NGSI-v2
NGSI-LD