Parse JSON Path

Ignition
1

I need to parse a JSON path in a format similar to how it is done with the JSON functions in MSSQL. However I don’t really want to add the external library jsonpath-ng to make it happen. I know that GSON is used quite frequently, and with all of perspective being stored in JSON, is this something that a built in function already covers?

Example:

I have JSON

{
  "level1":
  {
    "level2":{
      "finalKey": "value"
    }
  },
  "otherKey":"someValue"
}

And I need to get the value for $.level1.level2.finalKey to equal “value”

My guess/hope is that there is a function that executes the jsonGet expression that I could potentially leverage to extrapolate this.

2

Probably the closest first-party would be JsonUtilities.read - but you’ll probably have to do some type coercion from your original JSON (probably raw Python dicts?) to the GSON-based classes we use internally.

3

Put together:

from com.inductiveautomation.ignition.common import TypeUtilities, JsonUtilities

d = {
  "level1":
  {
    "level2":{
      "finalKey": "value"
    }
  },
  "otherKey":"someValue"
}

def get(json, path):
	gson = TypeUtilities.pyToGson(json)
	return JsonUtilities.read(gson, path).orElse(None)
	
print get(d, "level1.level2.finalKey")
1 Like
4

You are the best Paul! This is perfect.

5

Another note, incase you wanted this to be all in python for testing purposes. You could use reduce as well to solve this, I just realized this after going through Pauls example.

from functools import reduce
import operator

def find(element, json):
    return reduce(operator.getitem, element.split('.'), json)
    
d = {
  "level1":
  {
    "level2":{
      "finalKey": "value"
    }
  },
  "otherKey":"someValue"
}

print find("level1.level2.finalKey", d)
1 Like
6

That will limit you to object keys without allowing array addressing, though. You could split the difference and just use JsonPath.parse() and then extract the elements.