JSONata - Application Notes - Part 2

Try these expressions in the JSONata Exerciser. Link :  http://try.jsonata.org/Sy7Qw2Qvf

Original JSON:

{

"applicationID": "1",

"applicationName": "test_ds18b20",

"deviceName": "arduino_uno",

"devEUI": "1234567890123456",

"rxInfo": [{

"mac": "aa755a0048050130",

"rssi": -57,

"loRaSNR": 10,

"name": "raspberry_pi",

"latitude": 48.466860686785175,

"longitude": 35.019478797912605,

"altitude": 0

}],

"txInfo": {

"frequency": 868100000,

"dataRate": {

"modulation": "LORA",

"bandwidth": 125,

"spreadFactor": 7

},

"adr": true,

"codeRate": "4/5"

},

"fCnt": 9,

"fPort": 1,

"data": "Z29vZGJ5ZQ==",

"object": {}

}

Expression:  $keys()

Result:

[

  "applicationID",

  "applicationName",

  "deviceName",

  "devEUI",

  "rxInfo",

  "txInfo",

  "fCnt",

  "fPort",

  "data",

  "object"

]

Expression:  **.$keys()

Result:

[

  "applicationID",

  "applicationName",

  "deviceName",

  "devEUI",

  "rxInfo",

  "txInfo",

  "fCnt",

  "fPort",

  "data",

  "object",

  "mac",

  "rssi",

  "loRaSNR",

  "name",

  "latitude",

  "longitude",

  "altitude",

  "frequency",

  "dataRate",

  "adr",

  "codeRate",

  "modulation",

  "bandwidth",

  "spreadFactor"

]

Expression:  **.$keys()[0]

Result:

[

  "applicationID",

  "mac",

  "frequency",

  "modulation"

]

Expression:  **.$keys()[1]

Result:

[

  "applicationName",

  "rssi",

  "dataRate",

  "bandwidth"

]

Expression:  **.$keys()[2]

Result:

[

  "deviceName",

  "loRaSNR",

  "adr",

  "spreadFactor"

]

Expression:  **.$keys()[14]

Result:

** no match **

Expression:  (**.$keys())[14]

Result:

"latitude"

Expression:  (**.$keys())[[14..18]]

Result:

[

  "latitude",

  "longitude",

  "altitude",

  "frequency",

  "dataRate"

]

JSONata - Application Notes - Part 1

JSONata capabilities can be used in two Node-RED nodes: Change and Switch.

Advantages of using JSONata:

• its use is optional 
• can easy the development of Node-RED flows
• results in less use of code in function nodes
• it is really powerful to handle JSON structures
• has a nice and helpful web application named "JSONata Exerciser" to test expressions

Disadvantages of using JSONata

• need to learn a specific sintax
• makes hard for someone to understand a Node-RED flow if this person is not acquainted with JSONata

Example 1 - Doing a calculation

Example 2- Transform a given JSON data set to a new structure

Original Data set:

{
  "payload": [
    {
      "description": "Text 1",
      "id": "001"
    },
    {
      "description": "Text 2",
      "id": "002"
    },
    {
      "description": "Text 3",
      "id": "003"
    },
    {
      "description": "Text 4",
      "id": "004"
    }
  ]
}

JSONata expression

payload.{description:id}

Transformed data set:

[{

"Text 1": "001"

},

{

"Text 2": "002"

},

{

"Text 3": "003"

},

{

"Text 4": "004"

}

]

JSONata expression

payload{description:id}

Transformed data set:

{

"Text 1": "001",

"Text 2": "002",

"Text 3": "003",

"Text 4": "004"

}

JSONata expression

payload.[id, description]

Transformed data set:

[

[

"001",

"Text 1"

],

[

"002",

"Text 2"

],

[

"003",

"Text 3"

],

[

"004",

"Text 4"

]

]

Example 3- Transform a given JSON data set to a new structure

Original Data set:

[{

"series": [

""

],

"data": [

[

16.8192,

18.8832,

11.2728,

9.614400000000002

]

],

"labels": [

"sáb. 30 dic.",

"dom. 31 dic.",

"lun. 01 ene.",

"mié. 03 ene."

]

}]

JSONata expression, using the map function

$map(data, function($v, $i, $a) {

   {"date":labels[$i],"value":$v}

})

Resulting structure:

[

{

"date": "sáb. 30 dic.",

"value": 16.8192

},

{

"date": "dom. 31 dic.",

"value": 18.8832

},

{

"date": "lun. 01 ene.",

"value": 11.2728

},

{

"date": "mié. 03 ene.",

"value": 9.6144

}

]