Support more than string for Sensor.metadata

[matthijskooijman]

Reading the SensorThings 1.1 spec for Sensor, I see:

Field: metadata
Description: The detailed description of the Sensor or system. The metadata type is defined by encodingType.
Datatype: Any (depending on the value of the encodingType)

In my interpretation, this means that the metadata field can contain any valid JSON value. I wanted to put a JSON sensorml description directly in the metadata field as an object (not a string-encoded JSON), which I think the spec should allow:

{
        "name": "Si7021",
        "description": "Si7021 temperature and humidity sensor",
        "encodingType": "application/sml+json",
        "metadata": {
          "type": "PhysicalComponent",
          "name": "temp_humid_sensor",
          "definition": "http://www.w3.org/ns/sosa/System",
          "label": "Si7021 Temperature/Humidity Sensor",
          "identifiers": [
              "definition": "http://sensorml.com/ont/swe/property/ModelNumber",
              "label": "Model Number",
              "value": "Si7021"
            }
          ]
        }
 }

However, it seems FROST requires specifying a string for metadata:

{"code":400,"type":"error","message":"Cannot deserialize value of type  java.lang.String  from Object value (token  JsonToken.START_OBJECT )  at  Source: REDACTED ( StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION  disabled); line: 1, column:"}

FROST-Server/Plugins/CoreModelV2/src/main/resources/plugincoremodelv2/model/Sensor.json

Lines 73 to 74 in 785067a

	"name": "metadata",
	"type": "Edm.String",

Am I misinterpreting the spec, or is this just not implemented in FROST. Could it be implemented? It seems this would be similar to how "properties" already works, except that is always an object, and this could also be other JSON types.

[hylkevds]

Indeed, it seems you're the first one to try to put a non-string in there :)
It should not be too hard to make the field also accept JSON. The database table doesn't need to change for that.