CODEWITHSUNDEEP
f#type-providersf#-data
Coding Edgar
Coding Edgar

Reputation: 1455

FSharp.Data.JsonProvider optional property

I'm using the FSharp.Data.TypeProvider but I have an optional property that is not rendered as such.

I have this example JSON:

[
  {
    "error": {
      "message": "Error validating access token: Session has expired on Friday, 24-Jul-20 16:00:00 PDT. The current time is Friday, 24-Jul-20 16:06:14 PDT.",
      "type": "OAuthException",
      "code": 190,
      "error_subcode": 463,
      "fbtrace_id": "A0yQG8l8ggauD5PMbYSnEyA"
    }
  },
  {
    "error": {
      "message": "Error validating access token: Session has expired on Friday, 24-Jul-20 16:00:00 PDT. The current time is Friday, 24-Jul-20 16:06:14 PDT.",
      "type": "OAuthException",
      "code": 190,
      "error_subcode": 463,
      "fbtrace_id": "A0yQG8l8ggauD5PMbYSnEyA"
    }
  },
  {
    "data": [
      {
        "id": "17841511906082530"
      }
    ]
  }
]

The field error is read as Optional<Error> meanwhile the field data is Datum [], It should be Optional<Data>, this error seems to have something to do with the array, if I change the value of data to another type, like a number, it correctly infers the type.

Maybe is some cache that's wrong? How could I reset the TypeProvider cache?

OR am I doing something else wrong?

This issue is also reported in the github project: https://github.com/fsharp/FSharp.Data/issues/1322

Upvotes: 0

Views: 348

Answers (1)

Nghia Bui
Nghia Bui

Reputation: 3784

That's expected behavior.

In your JSON string, data is an array, an empty array indicates None, thus the field Data is read as array. That makes sense.

The fact that each element of that array belongs to type Datum also makes sense because Datum is the single form of Data (plural form). Indeed, if you rename data to dogs you will see it is read as Dog [].

Update: I don’t think we can tell the type provider to infer the field data as Option<Datum[]>. To check whether it is actually an empty array or not existed, we need to examine the JsonValue field:

match node.JsonValue with
| JsonValue.Record [|("data", _)|] ->
    // yep, we have field data here
| _ ->
    // nope, field data is missed

Upvotes: 1

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