15. Merge Patch Operation

Merge Patch procedure modifies an existing NGSI-LD element by applying the set of changes found in an NGSI-LD Fragment data to the target resource. Unlike the partial update patch behaviour which replaces the complete element on the first level, e.g. a whole Attribute

This operation allows modification of an existing NGSI-LD Entity by adding new Attributes (Properties or Relationships) or modifying or deleting existing Attributes associated with an existing Entity by calling a single API.

Merge Patch Operation process:

1. append those attributes that doesnot exist in existing data.

2. updated the value if attribute exist.

3. delete those attribute whose value is “urn:ngsi-ld:null”.

15.1. Example for Merge Patch Operation

15.1.1. 1. Create Operation

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

{
    "id": "urn:ngsi-ld:smartHospital:room01",
    "type": "Room",
    "temperatureSensor": {
        "type": "Property",
        "value": "23",
        "unit": {
            "type": "Property",
            "value": "CEL"
        },
        "observedAt": "2023-06-28T13:21:00.000Z"
    },
    "humiditySensor": {
        "type": "Property",
        "value": 22
    },
    "address": {
        "type": "Property",
        "value": {
            "roomno": 2,
            "streetaddress": "luxemburg"
        }
    },
    "isPartOf": {
        "type": "Relationship",
        "object": "urn:ngsi-ld:smartHospital"
    }
}

15.1.2. 2. Merge Patch Operation

We can modify existing NGSI-LD Entity by adding new Attributes (Properties or Relationships) or modifying or deleting existing Attributes associated with an existing Entity. For that we can hit the endpoint PATCH - http://<IP Address>:<port>/ngsi-ld/v1/entities/urn:ngsi-ld:smartHospital:room01 with the given payload

{
    "temperatureSensor": {
        "type": "Property",
        "value": 32.7,
        "observedAt": "2023-06-28T14:21:00.000Z"
    },
    "humiditySensor": {
        "type": "Property",
        "value": "urn:ngsi-ld:null"
    },
    "address": {
        "type": "Property",
        "value": {
            "roomno": 13,
            "streetaddress": "luxemburg"
        }
    }
}

15.1.3. 3. Query Operation

In order to retrieve the Entity details after Merge Patch operation, make a GET request with URL http://<IP Address>:<port>/ngsi-ld/v1/entities/urn:ngsi-ld:smartHospital:room01

Response:

{
    "id": "urn:ngsi-ld:smartHospital:room01",
    "type": "Room",
    "temperatureSensor": {
        "type": "Property",
        "value": 32.7,
        "unit": {
            "type": "Property",
            "value": "CEL"
        },
        "observedAt": "2023-06-28T14:21:00.000Z"
    },
    "address": {
        "type": "Property",
        "value": {
            "roomno": 13,
            "streetaddress": "luxemburg"
        }
    },
    "isPartOf": {
        "type": "Relationship",
        "object": "urn:ngsi-ld:smartHospital"
    }
}

Here, after retrieving the entity, we can see that the attributes “temperatureSensor” and “address” have been updated, and the attribute “humiditySensor” is removed.