You can use nested SELECT clauses to query for attributes within arrays and inner JSON objects. Supported by SQL version 2016-03-23 and later.
Consider the following MQTT message:
{
"e": [
{ "n": "temperature", "u": "Cel", "t": 1234, "v": 22.5 },
{ "n": "light", "u": "lm", "t": 1235, "v": 135 },
{ "n": "acidity", "u": "pH", "t": 1235, "v": 7 }
]
}Example
You can convert values to a new array with the following rule.
SELECT (SELECT VALUE n FROM e) as sensors FROM 'my/topic'
The rule generates the following output.
{
"sensors": [
"temperature",
"light",
"acidity"
]
}Example
Using the same MQTT message, you can also query a specific value within a nested object with the following rule.
SELECT (SELECT v FROM e WHERE n = 'temperature') as temperature FROM 'my/topic'
The rule generates the following output.
{
"temperature": [
{
"v": 22.5
}
]
}Example
You can also flatten the output with a more complicated rule.
SELECT get((SELECT v FROM e WHERE n = 'temperature'), 0).v as temperature FROM 'topic'
The rule generates the following output.
{
"temperature": 22.5
}