13. Implicit Attribute by q

According to the new specifications we can use “ngsi-ld/v1/entities?q=attrX” for querying the data which we called as Implicit Attribute by q.

• For the GET API to add the /ngsi-ld/v1/entities?q=attrX and based on q to identify this request and get response data.

• The NGSI-LD query language allows filtering entities according to the existence of attributes.

• For example: GET “/entities?q=attrX” will return only those entities that have an attribute called attrX. Regardless of the value of said attribute, if you instead want to filter on a value of an attribute: GET “/entities?q=attrX==12”

13.1. Example for Implicit Attribute by q

13.1.1. 1. Create Operation

In order to create an entity, we can hit the endpoint POST http://<IP Address>:<port>/ngsi-ld/v1/entities/ with the given payload.

{
    "id": "urn:ngsi-ld:Vehicle:A100",
    "type": "Vehicle",
    "brandName": {
        "type": "Property",
        "value": "Swift"
    },
    "isParked": {
        "type": "Relationship",
        "providedBy": {
            "type": "Relationship",
            "object": "urn:ngsi-ld:Person:Bob"
        },
        "object": "urn:ngsi-ld:OffStreetParking:Downtown1"
    },
    "speed": {
        "type": "Property",
        "value": 27
    },
    "temperature": {
        "type": "Property",
        "value": 25,
        "unitCode": "CEL"
    },
    "location": {
        "type": "GeoProperty",
        "value": {
            "type": "Point",
            "coordinates": [
                -8.6,
                41.6
            ]
        }
    }
}

13.1.2. 2. Query Operation

To retrieve entity with implicit attribute by q, you can send an HTTP GET to - http://<IP Address>:<port>/ngsi-ld/v1/entities?q={attrX} and we will get all the entities that have an attribute called attrX.

EXAMPLE: Give back the Entities whose speed is equals to 27

GET - http://localhost:9090/ngsi-ld/v1/entities?q=speed==27

Response:

[
    {
        "id": "urn:ngsi-ld:Vehicle:A100",
        "type": "Vehicle",
        "brandName": {
            "type": "Property",
            "value": "Swift"
        },
        "isParked": {
            "type": "Relationship",
            "providedBy": {
                "type": "Relationship",
                "object": "urn:ngsi-ld:Person:Bob"
            },
            "object": "urn:ngsi-ld:OffStreetParking:Downtown1"
        },
        "speed": {
            "type": "Property",
            "value": 27
        },
        "temperature": {
            "type": "Property",
            "value": 25,
            "unitCode": "CEL"
        },
        "location": {
            "type": "GeoProperty",
            "value": {
                "type": "Point",
                "coordinates": [
                    -8.6,
                    41.6
                ]
            }
        }
    }
]