问题
It is my first question on SO...so do not judge strictly =)
Usually all my questions techout in chat rooms (believe me, a lot of them =)).
Recently, we are talking about the RosettaCode. And I wondered to complement some of the tasks code to F#
One of them is JSON.
One of the possible solutions is the use of "F# Data: JSON Parser". So my question is linked with it.
This code works well:
open FSharp.Data
open FSharp.Data.JsonExtensions
type Person = {ID: int; Name:string}
let json = """[ { "ID": 1, "Name": "First" }, { "ID": 2, "Name": "Second" }]"""
json |> printfn "%s"
match JsonValue.Parse(json) with
| JsonValue.Array(x) ->
x |> Array.map(fun x -> {ID = System.Int32.Parse((x?ID).ToString()); Name = (string x?Name)})
| _ -> failwith "fail json"
|> Array.iter(fun x -> printfn "%i %s" x.ID x.Name)
Print:
[ { "ID": 1, "Name": "First" }, { "ID": 2, "Name": "Second" }]
1 "First"
2 "Second"
But it
{ID = System.Int32.Parse((x?ID).ToString()); Name = (string x?Name)}
doesn't look good.
This I read about JsonExtensions,
but when I use
{ID = (x?ID.AsInteger()) ; Name = (x?Name.AsString()) }
I get compile errors:
The field, constructor or "AsInteger" is not defined
The field, constructor or "AsString" is not defined
Strangely, thing is that I see accessibility through "open FSharp.Data.JsonExtensions"
So, question: How to use JsonExtensions?
回答1:
I tried to reproduce this using a minimal example, but I do not get the error - can you try the following minimal sample?
#r "...../FSharp.Data.dll"
open FSharp.Data.JsonExtensions
open FSharp.Data
JsonValue.Parse("A").AsArray()
|> Array.map (fun a -> a?ID.AsInteger())
I do not get auto-completion on a?ID.
(which is a limitation of the editor), but it compiles fine.
The only reason why I think this could be not working is if you had another open
declaration that would import another implementation of the ?
operator that is not returning JsonValue
.
The JsonValue
API is certainly not as nice as just using the type provider - so if you can, I'd probably go for the type provider instead (the low-level API is good if you need to iterate over everything in JSON recursively).
来源:https://stackoverflow.com/questions/33056348/f-data-json-parser-using-jsonextensions