ISO8601 string unpickle gives unable to cast object of type 'DateTime' to type 'String'.

[philderbeast]

#r "../packages/FsPickler/lib/net45/FsPickler.dll"
#r "../packages/FsPickler.Json/lib/net45/FsPickler.Json.dll"

fsi.PrintLength <- 1000
fsi.PrintWidth <- 1000

open System
open Nessos.FsPickler.Json

let json = FsPickler.CreateJsonSerializer(indent = true)

type GenericRecord<'T> = { GValue : 'T }
type GenericRecordAsString = GenericRecord<string>

let a0 = json.PickleToString<string>("a")
let a0' = json.UnPickleOfString<string>(a0)

let a1 = json.PickleToString<GenericRecordAsString>({ GValue = "a" })
let a1' = json.UnPickleOfString<GenericRecordAsString>(a1)

let b0 = json.PickleToString<string>("2013-10-30T16:00:00")
let b0' = json.UnPickleOfString<string>(b0)

let b1 = json.PickleToString<GenericRecordAsString>({ GValue = "2013-10-30T16:00:00" })
let b1' = json.UnPickleOfString<GenericRecordAsString>(b1)

In the above, the string -> a -> a' pickle (string -> a) and unpickle (a -> a') conversions work as does the ISO 8601 string -> b pickle but the b -> b' unpickle fails with the exception ...

Nessos.FsPickler.FsPicklerException: Error deserializing object of type 'System.String'. ---> System.InvalidCastException: Unable to cast object of type 'System.DateTime' to type 'System.String'

The ISO 8601 string -> b0 pickle looks good as does the ISO 8601 string -> b1 ..

val b0 : string = "{
  "FsPickler": "1.4.0",
  "type": "System.String",
  "value": "2013-10-30T16:00:00"
}"

val b1 : string = "{
  "FsPickler": "1.4.0",
  "type": "FSI_0004+GenericRecord`1[System.String]",
  "value": {
    "GValue": "2013-10-30T16:00:00"
  }
}"

[eiriktsarpalis]

I think this happens because JsonReader from Json.NET proactively parses the entry as DateTime based on the string content. This is further indication that we should move away from Json.NET altogether.

[philderbeast]

When using the JsonReader from Json.NET, after calling .Read() the .Value is of type DateTime. Is there the option of calling .ReadString() instead when reading a primitive as a string?

[eiriktsarpalis]

There is ReadAsString(), but for reasons that I cannot entirely remember, I chose to go for the .Value approach. I'll have a go at re-evaluating that choice.

[philderbeast]

Snappy turnaround time on this and good to be able to opt out of date parse handling.