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Flumoxed by addProperty to JSON Object!

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Posted on by DaveF1

Hi all - would really appreciate some help here. The end game is to dynamically add properties and values to a simple JSON object. But I'm falling at even the proof of concept stage witht he below really simple flow.. in the below addProperty doesn't seem to be updating the object, or in not the way I assumed it would.

the addProperty expression in AddFirstProperty :

addProperty(variables('ObjJSON'), 'PropertyName', 'PropertyValue')

(AddSecondProperty is the same except different PropertyName & PropertyValue)

So I would be expect something like the below in the output from the final step that I could then parse but it just shows as empty inside the curly brackets

{

"PropertyName" : "PropertyValue",

"PropertyName-2" : "PropertyValue-2"

}

Help much appreciated,

thanks

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cchannon 4,702 Moderator on at

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You can't add a property to a json string, you can only add it to a deserialized json object. use the ParseJSON operation first, then addProperty to that (and make sure you only feed addProperty objects so it can properly infer type - if you just try to addProperty(myobj, "test", "test") it will fail).

addProperty(body('Parse_JSON'), variables('test2'), variables('test2'))

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DaveF1 11 on at

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thanhs cchannon (especially as I posted this in the wrong place).
So you can't:
1) Initialize an object {}
2) add properties to that object inside a loop
3) de-serialize the object later to access what you've added.

Instead you addProperties to the deserialized object - then Set variable to overwrite the original empty object with added properties

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cchannon 4,702 Moderator on at

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Yeah, pretty much. All of the operations in Power Automate yield output values, but aren't inherrently variable modifiers; There isn't really a native "just do this operation on that value" kind of syntax. Instead, everything is about an output and then you assign that output to a thing (or in this case, back to the original obj)

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DaveF1 11 on at

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Thanks cchannon - that's a relaly helpful explanantion - wish I'd asked a couple of days ago rather than consult chatgpt!! Cheers mate

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