FIWARE Core Context Management NGSI LD JSON LD

Description: This tutorial teaches NGSI-LD users about CRUD Operations. The tutorial outlines example usage of the various ways of amending context as detailed within the NGSI-LD specification. A series of entities representing temperature sensors are created, modified and deleted based on the temperature sensor model defined in an earlier tutorial.

The tutorial uses cUrl commands throughout, but is also available as Postman documentation.

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NGSI-LD CRUD Operations

“Ninety-percent of everything is crud.”

― Theodore Sturgeon, Venture Science Fiction Magazine

CRUD Operations (Create, Read, Update and Delete) are the four basic functions of persistent storage. For a smart system based on NGSI-LD, CRUD actions allow the developer to manipulate the context data within the system. Every CRUD operation is clearly defined within the NGSI-LD specification, so all NGSI-LD compliant context brokers offer the same interface with the same NGSI-LD operations.

This tutorial will describe the rational behind each operation, when to use it and how to execute the various CRUD operations. Since NGSI-LD is based on JSON-LD passing of @context as part of each request in mandatory. For CRUD operations this is typically passed as a Link header, although as we have seen is also possible to pass an @context attribute as part of the body of the request if Content-Type: application/ld+json. However for GET requests, the @context cannot be placed in the payload body technique as GET requests have no body.

Context Entity CRUD Operations

There are four endpoints used for CRUD operations on an individual data entity. These follow the usual rules for hierarchical entities within RESTful applications.

For operations where the <entity-id> is not yet known within the context, or is unspecified, the /ngsi-ld/v1/entities endpoint is used. As an example, this is used for creating new entities.

Once an <entity-id> is known within the context, individual data entities can be manipulated using the /ngsi-ld/v1/entities/<entity-id> endpoint.

General Attribute operations on a known entity occur on the /ngsi-ld/v1/entities/<entity-id>/attrs endpoint and operations on individual attributes occur on the /ngsi-ld/v1/entities/<entity-id>/attrs/<attr-id>.

When requesting data or modifying individual entities, the various CRUD operations map naturally to HTTP verbs.

  • GET - for reading data
  • POST - for creating new entities and attributes
  • PATCH - for amending entities and attributes
  • DELETE - for deleting entities and attributes

Context Entity Batch Operations

Batch operations allow users to modify multiple data entities with a single request. All batch operations are mapped to the POST HTTP verb.

  • /entityOperations/create
  • /entityOperations/update
  • /entityOperations/upsert
  • /entityOperations/delete

Architecture

The demo application will send and receive NGSI-LD calls to a compliant context broker. Since the standardized NGSI-LD interface is available across multiple context brokers, so we only need to pick one - for example the Orion Context Broker. The application will therefore only make use of one FIWARE component.

Currently, the Orion Context Broker relies on open source MongoDB technology to keep persistence of the context data it holds.

To promote interoperability of data exchange, NGSI-LD context brokers explicitly expose a JSON-LD @context file to define the data held within the context entities. This defines a unique URI for every entity type and every attribute so that other services outside of the NGSI domain are able to pick and choose the names of their data structures. Every @context file must be available on the network. In our case the tutorial application will be used to host a series of static files.

Therefore, the architecture will consist of three elements:

  • The Orion Context Broker which will receive requests using NGSI-LD
  • The underlying MongoDB database :
    • Used by the Orion Context Broker to hold context data information such as data entities, subscriptions and registrations
  • The Tutorial Application does the following:
    • Offers static @context files defining the context entities within the system.

Since all interactions between the three elements are initiated by HTTP requests, the elements can be containerized and run from exposed ports.

The necessary configuration information can be seen in the services section of the associated orion-ld.yml file:

Orion-LD Configuration

orion:
    image: fiware/orion-ld
    hostname: orion
    container_name: fiware-orion
    depends_on:
        - mongo-db
    networks:
        - default
    ports:
        - "1026:1026"
    command: -dbhost mongo-db -logLevel DEBUG
    healthcheck:
        test: curl --fail -s http://orion:1026/version || exit 1
mongo-db:
    image: mongo:3.6
    hostname: mongo-db
    container_name: db-mongo
    expose:
        - "27017"
    ports:
        - "27017:27017"
    networks:
        - default
    command: --nojournal
tutorial:
    image: fiware/tutorials.ngsi-ld
    hostname: tutorial
    container_name: fiware-tutorial
    networks:
        default:
            aliases:
                - context
    expose:
        - 3000

The necessary configuration information can be seen in the services section of the associated docker-compose.yml file. It has been described in a previous tutorial

Start Up

All services can be initialised from the command-line by running the services Bash script provided within the repository. Please clone the repository and create the necessary images by running the commands as shown:

git clone https://github.com/FIWARE/tutorials.CRUD-Operations.git
cd tutorials.CRUD-Operations
git checkout NGSI-LD

./services orion|scorpio

Note: If you want to clean up and start over again you can do so with the following command:

./services stop


Create Operations

Create Operations map to HTTP POST.

  • The /ngsi-ld/v1/entities endpoint is used for creating new entities
  • The /ngsi-ld/v1/entities/<entity-id>/attrs endpoint is used for adding new attributes

Any newly created entity must have id and type attributes and a valid @context definition. All other attributes are optional and will depend on the system being modelled. If additional attributes are present though, each should specify both a type and a value.

The response will be 201 - Created if the operation is successful or 409 - Conflict if the operation fails.

Create a New Data Entity

This example adds a new TemperatureSensor entity to the context.

1 Request:

curl -iX POST 'http://localhost:1026/ngsi-ld/v1/entities/' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
--data-raw '{
      "id": "urn:ngsi-ld:TemperatureSensor:001",
      "type": "TemperatureSensor",
      "category": {
            "type": "Property",
            "value": "sensor"
      },
      "temperature": {
            "type": "Property",
            "value": 25,
            "unitCode": "CEL"
      }
}'

New entities can be added by making a POST request to the /ngsi-ld/v1/entities endpoint.

The request will fail if the entity already exists in the context.

2 Request:

You can check to see if the new TemperatureSensor can be found in the context by making a GET request

curl -L -X GET 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"'

Create New Attributes

This example adds a new batteryLevel Property and a controlledAsset Relationship to the existing TemperatureSensor entity with id=urn:ngsi-ld:TemperatureSensor:001.

3 Request:

curl -iX POST 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001/attrs' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
--data-raw '{
       "batteryLevel": {
            "type": "Property",
            "value": 0.9,
            "unitCode": "C62"
      },
      "controlledAsset": {
            "type": "Relationship",
            "object": "urn:ngsi-ld:Building:barn002"
      }
}'

New attributes can be added by making a POST request to the /ngsi-ld/v1/entities/<entity>/attrs endpoint.

The payload should consist of a JSON object holding the attribute names and values as shown.

All type=Property attributes must have a value associated with them. All type=Relationship attributes must have an object associated with them which holds the URN of another entity. Well-defined common metadata elements such as unitCode can be provided as strings, all other metadata should be passed as a JSON object with its own type and value attributes

Subsequent requests using the same id will update the value of the attribute in the context.

4 Request:

You can check to see if the new TemperatureSensor can be found in the context by making a GET request

curl -L -X GET 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"'

As you can see there are now two additional attributes (batteryLevel and controlledAsset) added to the entity. These attributes have been defined in the @context as part of the Device model and therefore can be read using their short names.

Batch Create New Data Entities or Attributes

This example uses the convenience batch processing endpoint to add three new TemperatureSensor entities to the context. Batch create uses the /ngsi-ld/v1/entityOperations/create endpoint.

5 Request:

curl -iX POST 'http://localhost:1026/ngsi-ld/v1/entityOperations/create' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-H 'Accept: application/ld+json' \
--data-raw '[
    {
      "id": "urn:ngsi-ld:TemperatureSensor:002",
      "type": "TemperatureSensor",
      "category": {
            "type": "Property",
            "value": "sensor"
      },
      "temperature": {
            "type": "Property",
            "value": 20,
            "unitCode": "CEL"
      }
    },
    {
      "id": "urn:ngsi-ld:TemperatureSensor:003",
      "type": "TemperatureSensor",
      "category": {
            "type": "Property",
            "value": "sensor"
      },
      "temperature": {
            "type": "Property",
            "value": 2,
            "unitCode": "CEL"
      }
    },
     {
      "id": "urn:ngsi-ld:TemperatureSensor:004",
      "type": "TemperatureSensor",
      "category": {
            "type": "Property",
            "value": "sensor"
      },
      "temperature": {
            "type": "Property",
            "value": 100,
            "unitCode": "CEL"
      }
    }
]'

The request will fail if any of the attributes already exist in the context. The response highlights which actions have been successful and the reason for failure (if any has occurred).

{
    "@context": "http://context-provider:3000/data-models/ngsi-context.jsonld",
    "success": [
        "urn:ngsi-ld:TemperatureSensor:002",
        "urn:ngsi-ld:TemperatureSensor:003",
        "urn:ngsi-ld:TemperatureSensor:004"
    ],
    "errors": []
}

Batch Create/Overwrite New Data Entities

This example uses the convenience batch processing endpoint to add or amend two TemperatureSensor entities in the context.

  • if an entity already exists, the request will update that entity's attributes.
  • if an entity does not exist, a new entity will be created.

6 Request:

curl -iX POST 'http://localhost:1026/ngsi-ld/v1/entityOperations/upsert' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-H 'Accept: application/ld+json' \
--data-raw '[
    {
      "id": "urn:ngsi-ld:TemperatureSensor:002",
      "type": "TemperatureSensor",
      "category": {
            "type": "Property",
            "value": "sensor"
      },
      "temperature": {
            "type": "Property",
            "value": 21,
            "unitCode": "CEL"
      }
    },
    {
      "id": "urn:ngsi-ld:TemperatureSensor:003",
      "type": "TemperatureSensor",
      "category": {
            "type": "Property",
            "value": "sensor"
      },
      "temperature": {
            "type": "Property",
            "value": 27,
            "unitCode": "CEL"
      }
    }
]'

Batch processing for create/overwrite uses the /ngsi-ld/v1/entityOperations/upsert endpoint.

A subsequent request containing the same data (i.e. same entities and actionType=append) will also succeed won't change the context state. The modifiedAt metadata will be amended however.

Read Operations

  • The /ngsi-ld/v1/entities endpoint is used for listing entities
  • The /ngsi-ld/v1/entities/<entity> endpoint is used for retrieving the details of a single entity.

For read operations the @context must be supplied in a Link header.

Filtering

  • The options parameter (combined with the attrs parameter) can be used to filter the returned fields
  • The q parameter can be used to filter the returned entities

Read a Data Entity (verbose)

This example reads the full context from an existing TemperatureSensor entity with a known id.

7 Request:

curl -G -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-d 'options=sysAttrs'

Response:

TemperatureSensor urn:ngsi-ld:TemperatureSensor:001 is returned as normalized NGSI-LD. Additional metadata is returned because options=sysAttrs. By default the @context is returned in the payload body (although this could be moved due to content negotiation if the Accept:application/json had been set. The full response is shown below:

{
    "@context": "http://context-provider:3000/data-models/ngsi-context.jsonld",
    "id": "urn:ngsi-ld:TemperatureSensor:001",
    "type": "TemperatureSensor",
    "createdAt": "2020-08-27T14:33:06Z",
    "modifiedAt": "2020-08-27T14:33:10Z",
    "category": {
        "type": "Property",
        "createdAt": "2020-08-27T14:33:06Z",
        "modifiedAt": "2020-08-27T14:33:06Z",
        "value": "sensor"
    },
    "temperature": {
        "type": "Property",
        "createdAt": "2020-08-27T14:33:06Z",
        "modifiedAt": "2020-08-27T14:33:06Z",
        "value": 25,
        "unitCode": "CEL"
    },
    "batteryLevel": {
        "value": 0.8,
        "type": "Property",
        "createdAt": "2020-08-27T14:33:10Z",
        "modifiedAt": "2020-08-27T14:33:10Z",
        "unitCode": "C62"
    },
    "controlledAsset": {
        "object": "urn:ngsi-ld:Building:barn002",
        "type": "Relationship",
        "createdAt": "2020-08-27T14:33:10Z",
        "modifiedAt": "2020-08-27T14:33:10Z"
    }
}

Individual context data entities can be retrieved by making a GET request to the /ngsi-ld/v1/entities/<entity> endpoint.

Read an Attribute from a Data Entity

This example reads the value of a single attribute (temperature) from an existing TemperatureSensor entity with a known id.

8 Request:

curl -G -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-d 'attrs=temperature'

Response:

The sensor urn:ngsi-ld:TemperatureSensor:001 is reading at 25°C. The response is shown below:

{
    "@context": "http://context-provider:3000/data-models/ngsi-context.jsonld",
    "id": "urn:ngsi-ld:TemperatureSensor:001",
    "type": "TemperatureSensor",
    "temperature": {
        "type": "Property",
        "value": 25,
        "unitCode": "CEL"
    }
}

Because options=keyValues was not used this is the normalized response including the metadata such as unitCode. Context data can be retrieved by making a GET request to the /ngsi-ld/v1/entities/<entity-id> endpoint and selecting the attrs using a comma separated list.

Read a Data Entity (key-value pairs)

This example reads the key-value pairs from the context of an existing TemperatureSensor entities with a known id.

9 Request:

curl -G -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001' \
-H 'Link: <http://context-provider:3000/data-models/json-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-H 'Accept: application/json' \
-d 'options=keyValues'

Response:

The sensor urn:ngsi-ld:TemperatureSensor:001 is reading at 25°C. The response is shown below:

{
    "id": "urn:ngsi-ld:TemperatureSensor:001",
    "type": "TemperatureSensor",
    "category": "sensor",
    "temperature": 25,
    "batteryLevel": 0.8,
    "controlledAsset": "urn:ngsi-ld:Building:barn002"
}

The response contains an unfiltered list of context data from an entity containing all of the attributes of the urn:ngsi-ld:TemperatureSensor:001. The payload body does not contain an @context attribute since the Accept: application/json was set.

Combine the options=keyValues parameter with the attrs parameter to retrieve a limited set of key-value pairs.

Read Multiple attributes values from a Data Entity

This example reads the value of two attributes (category and temperature) from the context of an existing TemperatureSensor entity with a known ID.

10 Request:

curl -G -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001' \
-H 'Link: <http://context-provider:3000/data-models/json-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-H 'Accept: application/json' \
-d 'options=keyValues' \
-d 'attrs=category,temperature'

Response:

The sensor urn:ngsi-ld:TemperatureSensor:001 is reading at 25°C. The response is shown below:

{
    "id": "urn:ngsi-ld:TemperatureSensor:001",
    "type": "TemperatureSensor",
    "category": "sensor",
    "temperature": 25
}

Combine the options=keyValues parameter and the attrs parameter to return a list of values.

List all Data Entities (verbose)

This example lists the full context of all TemperatureSensor entities.

11 Request:

curl -G -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-d 'type=TemperatureSensor'

Response:

On start-up the context was empty, four TemperatureSensor entities have been added by create operations so the full context will now contain four sensors.

[
    {
        "@context": "http://context-provider:3000/data-models/ngsi-context.jsonld",
        "id": "urn:ngsi-ld:TemperatureSensor:004",
        "type": "TemperatureSensor",
        "category": {
            "type": "Property",
            "value": "sensor"
        },
        "temperature": {
            "type": "Property",
            "value": 100,
            "unitCode": "CEL"
        }
    },
    {
        "@context": "http://context-provider:3000/data-models/ngsi-context.jsonld",
        "id": "urn:ngsi-ld:TemperatureSensor:002",
        "type": "TemperatureSensor",
        "category": {
            "type": "Property",
            "value": "sensor"
        },
        "temperature": {
            "type": "Property",
            "value": 21,
            "unitCode": "CEL"
        }
    },
    {
        "@context": "http://context-provider:3000/data-models/ngsi-context.jsonld",
        "id": "urn:ngsi-ld:TemperatureSensor:003",
        "type": "TemperatureSensor",
        "category": {
            "type": "Property",
            "value": "sensor"
        },
        "temperature": {
            "type": "Property",
            "value": 27,
            "unitCode": "CEL"
        }
    },
    {
        "@context": "http://context-provider:3000/data-models/ngsi-context.jsonld",
        "id": "urn:ngsi-ld:TemperatureSensor:001",
        "type": "TemperatureSensor",
        "batteryLevel": {
            "type": "Property",
            "value": 0.8,
            "unitCode": "C62"
        },
        "category": {
            "type": "Property",
            "value": "sensor"
        },
        "controlledAsset": {
            "type": "Relationship",
            "object": "urn:ngsi-ld:Building:barn002"
        },
        "temperature": {
            "type": "Property",
            "value": 25,
            "unitCode": "CEL"
        }
    }
]

List all Data Entities (key-value pairs)

This example lists the temperature attribute of all TemperatureSensor entities.

12 Request:

curl -G -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/' \
-H 'Link: <http://context-provider:3000/data-models/json-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-H 'Accept: application/json' \
-d 'type=TemperatureSensor' \
-d 'options=keyValues' \
-d 'attrs=temperature'

Response:

The full context contains four sensors, they are returned in a random order:

[
    {
        "id": "urn:ngsi-ld:TemperatureSensor:004",
        "type": "TemperatureSensor",
        "temperature": 100
    },
    {
        "id": "urn:ngsi-ld:TemperatureSensor:002",
        "type": "TemperatureSensor",
        "temperature": 21
    },
    {
        "id": "urn:ngsi-ld:TemperatureSensor:003",
        "type": "TemperatureSensor",
        "temperature": 27
    },
    {
        "id": "urn:ngsi-ld:TemperatureSensor:001",
        "type": "TemperatureSensor",
        "temperature": 25
    }
]

Full context data for a specified entity type can be retrieved by making a GET request to the /ngsi-ld/v1/entities endpoint and supplying the type parameter, combine this with the options=keyValues parameter and the attrs parameter to retrieve key-values.

Filter Data Entities by ID

This example lists selected data from two TemperatureSensor entities chosen by id. Note that every id must be unique, so type is not required for this request. To filter by id add the entries in a comma delimted list.

13 Request:

curl -G -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/'' \
-H 'Link: <http://context-provider:3000/data-models/json-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-H 'Accept: application/json' \
-d 'id=urn:ngsi-ld:TemperatureSensor:001,urn:ngsi-ld:TemperatureSensor:002' \
-d 'options=keyValues' \
-d 'attrs=temperature'

Response:

The response details the selected attributes from the selected entities.

[
    {
        "id": "urn:ngsi-ld:TemperatureSensor:002",
        "type": "TemperatureSensor",
        "temperature": 21
    },
    {
        "id": "urn:ngsi-ld:TemperatureSensor:001",
        "type": "TemperatureSensor",
        "temperature": 25
    }
]

Update Operations

Overwrite operations are mapped to HTTP PATCH:

  • The /ngsi-ld/v1/entities/<entity-id>/attrs/<attribute> endpoint is used to update an attribute
  • The /ngsi-ld/v1/entities/<entity-id>/attrs endpoint is used to update multiple attributes

Overwrite the value of an Attribute value

This example updates the value of the category attribute of the Entity with id=urn:ngsi-ld:TemperatureSensor:001

14 Request:

curl -iX PATCH 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001/attrs/category' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
--data-raw '{
    "value": ["sensor", "actuator"],
    "type": "Property"
}'

Existing attribute values can be altered by making a PATCH request to the /ngsi-ld/v1/entities/<entity-id>/attrs/<attribute> endpoint. The appropriate @context should be supplied as a Link header.

Overwrite Multiple Attributes of a Data Entity

This example simultaneously updates the values of both the category and controlledAsset attributes of the Entity with id=urn:ngsi-ld:TemperatureSensor:001.

15 Request:

curl -iX PATCH 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001/attrs' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
--data-raw '{
      "category": {
            "value": [
                  "sensor",
                  "actuator"
            ],
            "type": "Property"
      },
      "controlledAsset": {
            "type": "Relationship",
            "object": "urn:ngsi-ld:Building:barn001"
      }
}'

Batch Update Attributes of Multiple Data Entities

This example uses the convenience batch processing endpoint to update existing products.

16 Request:

curl -G -iX POST 'http://localhost:1026/ngsi-ld/v1/entityOperations/upsert' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-d 'options=update'
--data-raw '[
  {
    "id": "urn:ngsi-ld:TemperatureSensor:003",
    "type": "TemperatureSensor",
    "category": {
      "type": "Property",
      "value": [
        "actuator",
        "sensor"
      ]
    }
  },
  {
    "id": "urn:ngsi-ld:TemperatureSensor:004",
    "type": "TemperatureSensor",
    "category": {
      "type": "Property",
      "value": [
        "actuator",
        "sensor"
      ]
    }
  }
]'

Batch processing uses the /ngsi-ld/v1/entityOperations/upsert endpoint. The payload body holds an array of the entities and attributes we wish to update.The options=update parameter indicates we will not remove existing attributes if they already exist and have not been included in the payload.

An alternative would be to use the /ngsi-ld/v1/entityOperations/update endpoint. Unlike upsert, the update operation will not silently create any new entities - it fails if the entities do not already exist.

Batch Replace Entity Data

This example uses the convenience batch processing endpoint to replace entity data of existing sensors.

17 Request:

curl -G -iX POST 'http://localhost:1026/ngsi-ld/v1/entityOperations/update' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-d 'options=replace'
--data-raw '[
  {
    "id": "urn:ngsi-ld:TemperatureSensor:003",
    "type": "TemperatureSensor",
    "category": {
      "type": "Property",
      "value": [
        "actuator",
        "sensor"
      ]
    }
  },
  {
    "id": "urn:ngsi-ld:TemperatureSensor:004",
    "type": "TemperatureSensor",
    "temperature": {
      "type": "Property",
      "value": [
        "actuator",
        "sensor"
      ]
    }
  }
]'

Batch processing uses the /ngsi-ld/v1/entityOperations/update endpoint with a payload with the - options=replace parameter, this means we will overwrite existing entities. /ngsi-ld/v1/entityOperations/upsert could also be used if new entities are also to be created.

Delete Operations

Delete Operations map to HTTP DELETE.

  • The /ngsi-ld/v1/entities/<entity-id> endpoint can be used to delete an entity
  • The /ngsi-ld/v1/entities/<entity-id>/attrs/<attribute> endpoint can be used to delete an attribute

The response will be 204 - No Content if the operation is successful or 404 - Not Found if the operation fails.

Data Relationships

If there are entities within the context which relate to one another, you must be careful when deleting an entity. You will need to check that no references are left dangling once the entity has been deleted.

Organizing a cascade of deletions is beyond the scope of this tutorial, but it would be possible using a batch delete request.

Delete an Entity

This example deletes the entity with id=urn:ngsi-ld:TemperatureSensor:004 from the context.

18 Request:

curl -iX DELETE 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:004'

Entities can be deleted by making a DELETE request to the /ngsi-ld/v1/entities/<entity> endpoint.

Subsequent requests using the same id will result in an error response since the entity no longer exists in the context.

Delete an Attribute from an Entity

This example removes the batteryLevel attribute from the entity with id=urn:ngsi-ld:TemperatureSensor:001.

19 Request:

curl -L -X DELETE 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001/attrs/batteryLevel' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"'

Attributes can be deleted by making a DELETE request to the /ngsi-ld/v1/entities/<entity>/attrs/<attribute> endpoint. It is important to supply the appropriate @context in the request in the form of a Link header to ensure that the attribute name can be recognised.

If the entity does not exist within the context or the attribute cannot be found on the entity, the result will be an error response.

Batch Delete Multiple Entities

This example uses the convenience batch processing endpoint to delete some TemperatureSensor entities.

20 Request:

curl -L -X POST 'http://localhost:1026/ngsi-ld/v1/entityOperations/delete' \
-H 'Content-Type: application/json' \
--data-raw '[
  "urn:ngsi-ld:TemperatureSensor:002",
  "urn:ngsi-ld:TemperatureSensor:003"
]'

Batch processing uses the /ngsi-ld/v1/entityOperations/delete endpoint with a payload consisting of an array of elements to delete.

If an entity does not exist in the context, the result will be an error response.

Batch Delete Multiple Attributes from an Entity

This example uses the PATCH /ngsi-ld/v1/entities/<entity-id>/attrs endpoint to delete some attributes from a TemperatureSensor entity.

21 Request:

curl -L -X PATCH 'http://localhost:1026/ngsi-ld/v1/entities/urn:ngsi-ld:TemperatureSensor:001/attrs' \
-H 'Content-Type: application/json' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
--data-raw '{
      "category": {
            "value": null,
            "type": "Property"
      },
      "controlledAsset": {
            "type": "Relationship",
            "object": null
      }
}'

If a value is set to null the attribute is deleted.

Find existing data relationships

This example returns a header indicating whether any linked data relationships remain against the entity urn:ngsi-ld:Building:barn002

22 Request:

curl -iX GET 'http://localhost:1026/ngsi-ld/v1/entities/?type=TemperatureSensor&limit=0&count=true&q=controlledAsset==%22urn:ngsi-ld:Building:barn002%22' \
-H 'Link: <http://context-provider:3000/data-models/ngsi-context.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"' \
-H 'Accept: application/json'

Response:

[]

Because the limit=0 parameter has been used no entities are listed in the payload body, however the count=true means that the count is passed as a header instead:

NGSILD-Results-Count: 1

If limit was not present the payload would hold the details of every matching entity instead.