Structured values for attributes
Apart from simple values such as 22.5 or "yellow", you can use complex structures as attribute values. In particular, an attribute can be set to a vector or to a key-value map (usually referred to as an "object") at creation/update time. These values are retrieved at query and notification time.
Vector or key-map values correspond directly to JSON vectors and JSON objects, respectively. Thus, the following create entity request sets the value of attribute "A" to a vector and the value of attribute B to a key-map object (we show it in an entity creation operation, but the same applies to attribute updates).
In NGSIv2:
curl localhost:1026/v2/entities -s -S --header 'Content-Type: application/json' \
-d @- <<EOF
{
"id": "E1",
"type": "T",
"A": {
"type": "T",
"value": [
"22",
{
"x": [
"x1",
"x2"
],
"y": "3"
},
[
"z1",
"z2"
]
]
},
"B": {
"type": "T",
"value": {
"x": {
"x1": "a",
"x2": "b"
},
"y": [
"y1",
"y2"
]
}
}
}
EOF
In NGSIv1:
(curl localhost:1026/v1/updateContext -s -S --header 'Content-Type: application/json' \
--header 'Accept: application/json' -d @- | python -mjson.tool) <<EOF
{
"contextElements": [
{
"type": "T1",
"isPattern": "false",
"id": "E1",
"attributes": [
{
"name": "A",
"type": "T",
"value": [
"22",
{
"x": [
"x1",
"x2"
],
"y": "3"
},
[
"z1",
"z2"
]
]
},
{
"name": "B",
"type": "T",
"value": {
"x": {
"x1": "a",
"x2": "b"
},
"y": [
"y1",
"y2"
]
}
}
]
}
],
"updateAction": "UPDATE"
}
EOF
The value of the attribute is stored internally by Orion Context Broker in a format-independent representation.
Note that for NGSIv1 in order to align JSON representations, the final "leaf"
elements of the structured attribute values after traversing all vectors
and key-maps are always considered as strings. Thus, take into account that
although you can use for instance a JSON number as a field value in updates
(such as {"x": 3.2 }
), you will retrieve a string in queries and notifications
(i.e. { "x": "3.2"}
).
In NGSIv2, the final "leaf" elements of the structured attribute values after traversing
all vectors and key-maps uses the right native JSON type (number, boolean, etc.).
Thus, if you use for instance a JSON number as a field value in updates
(such as {"x": 3.2 }
), you will get also a number in queries
and notifications (i.e. { "x": 3.2}
).