Microsoft Foundry: How does it recognize the different fields of a json schema.

Question

So I am uploading the Json to agent(Inside workflow) and I want to check if some fields were missing or not in that Json from the user request. now I want to check this using if/else branching but I am unable to write the power function inside the condition block. How can we write the Custom Power Function for this query.
For e.g. I have defined one local variable named "request" and field to check is "missing_information" then how can we write the power query for the same to check if this was present or not in user's input?

Answer 1

Hi @Brijdeep Goyal ,

Two pieces are needed here — parsing first, then the condition.

1. Parse the JSON into a record (do this before the if/else). The if/else Condition box uses Power Fx, and you can only reference sub-fields (request.missing_information) if request is a structured record, not a raw JSON string. So make the JSON typed first, either way:

• Recommended – set the agent's output format to a JSON Schema: open the Invoke agent node → Details → the parameter icon → set Text format = JSON Schema, and paste your schema. The agent's saved output then becomes a record you can dot-access.
• Or add a Data transformation → Parse value node to parse the string into a typed value and save it to your request variable.

In your schema, declare the field you want to test as nullable so it can legitimately be absent (Foundry/structured outputs require every property to be required, so emulate "optional" with a null union):

{
  "missing_information": { "type": ["string", "null"] }
}

2. Write the condition with Power Fx. Local variables need the Local. scope prefix. To branch on whether the field is missing:

IsBlank(Local.request.missing_information)

• true → the field is missing/blank → route to your "missing" branch.
• To test the opposite (field is present), use:

!IsBlank(Local.request.missing_information)

IsBlank() returns true for blank/null/empty-string, which is exactly the "is this field there?" check. (If you needed to test an array/table field instead, use IsEmpty().)

Common gotchas

• "Name isn't valid" → missing scope prefix. Use Local. (local vars) or System. (system vars).
• "Type mismatch" → the value is still a string; parse it first (step 1), or wrap with Text() / Value().
• Remember to click Save in the visualizer — Foundry doesn't autosave.

Docs:

• Build a workflow in Microsoft Foundry – if/else with Power Fx & Configure a JSON Schema output
• IsBlank / IsEmpty / Coalesce (Power Fx)
• If function (Power Fx)

Hope this unblocks you!

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