Struggling with system.text.json

Question

I'm struggling with system.text.json. I have been using NewtonSoft for years, but I'm trying to migrate away from it to avoid dependencies on 3rd party libraries.  I'm trying to do something very simple, and I just don't get it. I am calling a web service which returns the result of a GIS query. I have previously successfully decoded these both with XML and NewtonSoft, but despite many attempts, I just don't get it. What I'm trying to do is very simple.

I want to detect case 1 where there are no results returned.
I want to detect case 2 where there are results returned and extract the "attributes"."name" field.

How hard could it be? Well, despite massive googling, I just can't work it out. I have tried both JsonDocument.Parse and JsonNode.Parse, but after the initial parse I just can't navigate to the correct field without type violations. I'm programming in VB.net, but an answer in any language should be fine.

1. No result {
   "results":[ ]
   }
2. Success result {
   "results":[
   {
   "layerId":31,
   "layerName":"Islands",
   "displayFieldName":"name",
   "value":"STEPHENS ISLAND",
   "attributes":{
   "OBJECTID":"5767",
   "featuretype":"Island",
   "name":"STEPHENS ISLAND",
   "state":"QLD",
   "featurereliability":"1/1/2004",
   "attributereliability":"9/14/2001",
   "planimetricaccuracy":"100",
   "source":"GEOSCIENCE AUSTRALIA",
   "ufi":"BC52900008",
   "creationdate":"5/9/2006",
   "retirementdate":"Null",
   "pid":"3491389",
   "symbol":"0",
   "SHAPE":"Polygon",
   "st_area(shape)":"0.000012",
   "st_perimeter(shape)":"0.016835"
   }
   }
   ]
   }

Answer 1

Hi @
I doing some tests based on the document How to serialize and deserialize (marshal and unmarshal) JSON in .NET and it works well.
Please try the following code.

Imports System.IO  
Imports System.Text.Json  
Imports System.Text.Json.Serialization  
  
Public Class Form1  
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click  
        Dim jsonString As String  
        Dim root As Root  
        jsonString = File.ReadAllText("C:\json.txt")  
        root = JsonSerializer.Deserialize(Of Root)(jsonString)  
        Console.WriteLine(root.results(0).attributes.name)  
    End Sub  
End Class  
  
  
Public Class Attributes  
    Public Property OBJECTID As String  
    Public Property featuretype As String  
    Public Property name As String  
    Public Property state As String  
    Public Property featurereliability As String  
    Public Property attributereliability As String  
    Public Property planimetricaccuracy As String  
    Public Property source As String  
    Public Property ufi As String  
    Public Property creationdate As String  
    Public Property retirementdate As String  
    Public Property pid As String  
    Public Property symbol As String  
    Public Property SHAPE As String  
    <JsonPropertyName("st_area(shape)")>  
    Public Property StAreaShape As String  
    <JsonPropertyName("st_perimeter(shape)")>  
    Public Property StPerimeterShape As String  
End Class  
  
Public Class Result  
    Public Property layerId As Integer  
    Public Property layerName As String  
    Public Property displayFieldName As String  
    Public Property value As String  
    Public Property attributes As Attributes  
End Class  
  
Public Class Root  
    Public Property results As List(Of Result)  
End Class  

Best Regards.
Jiachen Li

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