Нужна помощь по jsontextwriter

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Я новичок в Json и застрял на создании файла данных JSon для Ext.Net древесная панель.

Вот данные, которые я вручную набираю, и это работает для меня. И я хочу сгенерировать аналогичный формат данных из таблицы данных в VB.Net.

{
  "partcode": "",
  "threadid": "",
  "description": "",
  "specification": "",
  "parentId": null,
  "leaf": false,
  "children": [
    {
      "partcode": "609",
      "threadid": "",
      "description": "This is code 609",
      "specification": "Code 609 Spec",
      "parentId": "root",
      "leaf": false,
      "children": [
        {
          "partcode": "609B",
          "threadid": "",
          "description": "This is code 609B",
          "specification": "Code 609B Spec",
          "parentId": "609",
          "leaf": false,
          "children": [
            {
              "partcode": "609BLevel2",
              "threadid": "",
              "description": "This is code 609B Level 2",
              "specification": "Code 609BLevel2 Spec",
              "parentId": "609B",
              "leaf": false,
              "children": [
                {
                  "partcode": "609BLevel3",
                  "threadid": "",
                  "description": "This is code 609BLevel3",
                  "specification": "Code 609BLevel3 Spec",
                  "parentId": "609BLevel2",
                  "leaf": true
                }
              ]
            }
          ]
        },
        {
          "partcode": "B609/3",
          "threadid": "",
          "description": "This is code B609/3",
          "specification": "Code B609/3 Spec",
          "parentId": "609",
          "leaf": false,
          "children": [
            {
              "children": [
                {
                  "partcode": "B609/3 Level2",
                  "threadid": "",
                  "description": "This is code B609/3 Level 2",
                  "specification": "Code B609/3 Spec",
                  "parentId": "B609/3",
                  "leaf": false,
                  "children": [
                    {
                      "partcode": "B609/3 Level3",
                      "threadid": "",
                      "description": "This is code 609BLevel3",
                      "specification": "Code B609/3 Level3 Spec",
                      "parentId": "B609/3 Level2",
                      "leaf": true
                    }
                  ]
                }
              ]
            }
          ]
        }
      ]
    }
  ]
}

In my data table, 
NoIdx partcode     parent     description             specification
0     609          0_         This is code 609        Code 609 Spec
1     609B         609        This is code 609B       Code 609B Spec
2     609BLevel2   609B       This is code 609BLevel2 Code 609BLevel2 Spec
3     609BLevel3   609BLevel2 This is code 609BLevel3 Code 609BLevel3 Spec
1     B609/3       609        blah blah blah
2     B609/3Level2 B609/3     blah blah blah
3     B609/3Level3 B609/3Level2 blah blah...   

Что я уже пробовал:

Здесь ниже было то, что я пытался сделать, но это не работает. Кто-нибудь может помочь?

Dim dt As New DataTable
        'dt = oSQLClass.GetSQLTable("SELECT * FROM get_BomTree ('609', '609', 1 )")

        Try
            Dim dc As New myDataConnection
            Dim cn As New SqlClient.SqlConnection(dc.ConStringForSQLCommand)
            cn.Open()

            Dim sa As New SqlClient.SqlDataAdapter("SELECT * FROM get_BomTree ('609', '609', 1 )", cn)

            cn.Close() 'connection close here , that is disconnected from data source

            sa.Fill(dt)

        Catch ex As Exception

        End Try

        If dt.Rows.Count = 0 Then
            Exit Sub
        End If

     Using writer As Newtonsoft.Json.JsonWriter = New JsonTextWriter(sw)
            writer.Formatting = Formatting.Indented

            ''This is a root mark up
            ''-----------------------
            writer.WriteStartObject()
            writer.WritePropertyName("partcode")
            writer.WriteValue("")
            writer.WritePropertyName("description")
            writer.WriteValue("")
            writer.WritePropertyName("specification")
            writer.WriteValue("")
            writer.WritePropertyName("parentId")
            writer.WriteValue("root")
            writer.WritePropertyName("leaf")
            writer.WriteValue(False)

            Dim r As DataRow
            Dim rNext As DataRow = Nothing

            ''
            For i As Int16 = 0 To dt.Rows.Count - 1
                r = dt.Rows(i)
                If i + 1 <= dt.Rows.Count Then
                    rNext = dt.Rows(i + 1)
                Else
                    rNext = Nothing
                End If

                If r("NoIdx") = 0 Then
                    ''This is a FATHER
                    ''-----------------------
                    writer.WritePropertyName("children")
                    writer.WriteStartArray()
                    writer.WriteStartObject()
                    writer.WritePropertyName("partcode")
                    writer.WriteValue(Trim(r("partcode")))
                    writer.WritePropertyName("description")
                    writer.WriteValue(Trim(r("description")))
                    writer.WritePropertyName("specification")
                    writer.WriteValue(Trim(r("specification")))
                    writer.WritePropertyName("parentId")
                    writer.WriteValue(Trim(r("parent")))
                    writer.WritePropertyName("leaf")
                    writer.WriteValue(False) '' if have child then leaf=false
                    writer.WritePropertyName("children")
                    writer.WriteStartArray()
                Else
                    writer.WriteStartObject()
                    writer.WritePropertyName("partcode")
                    writer.WriteValue(Trim(r("partcode")))
                    writer.WritePropertyName("description")
                    writer.WriteValue(Trim(r("description")))
                    writer.WritePropertyName("specification")
                    writer.WriteValue(Trim(r("specification")))
                    writer.WritePropertyName("parentId")
                    writer.WriteValue(Trim(r("parent")))
                    writer.WritePropertyName("leaf")

                    If rNext IsNot Nothing Then
                        ''it has sub level
                        If CInt(rNext("NoIdx")) > r("NoIdx") Then
                            writer.WriteValue(False) '' continue add node in same level leaf=false
                            writer.WritePropertyName("children")
                            writer.WriteStartArray()
                        Else
                            If CInt(rNext("NoIdx")) = r("NoIdx") Then
                                writer.WriteValue(True) '' continue add node in same level leaf=false
                                writer.WriteEndObject()
                            Else
                                ''no more sub level
                                writer.WriteValue(True) '' cut off and add new level leaf= true

                                writer.WriteEndConstructor()

                            End If
                        End If
                    End If
                End If

            Next

            writer.WriteEnd()
            writer.WriteEndObject()
        End Using

     Dim file As System.IO.StreamWriter
        file = My.Computer.FileSystem.OpenTextFileWriter("C:\Users\User\Documents\File\TestData.Json", False)
        file.WriteLine(sb.ToString)
        file.Close()

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