Object is nothing after json deserialization - json

Question

I want to deserialize a json file into 'Artikelstammdaten' and afterwards to a list of 'Artikelstammdaten' (don't know how to iterate over the deserialized json yet). I already tried to deserialize it into the Rootobject, but the object was also "Nothing"Here is what i have tried:
If OpenfilePath IsNot Nothing Then
Dim asd As Artikelstammdaten
Dim fileReader As StreamReader
fileReader = My.Computer.FileSystem.OpenTextFileReader(OpenfilePath)
asd = JsonConvert.DeserializeObject(Of Artikelstammdaten)(fileReader.ReadToEnd)
End If
Edit: This is what the class structure looks like now:
Public Class Artikelstammdaten
Public Property Artikel As String
Public Property BezeichnungDE As String
Public Property BezeichnungEN As String
Public Property Einheit As String
Public Property MatGrp As String
Public Property Kostenart As Integer?
Public Property Vertriebstext_DE As String
Public Property Vertriebstext_EN As String
Public Property Stueckliste As String
Public Property Status As String
Public Property Klasse As String
Public Property Mantelflaeche As Double?
Public Property Gewicht As Integer?
Public Property KlasseID As String
End Class
Public Class Stueckliste
Public Property Verkaufsartikel As String
Public Property Position As Integer?
Public Property PosArtikel As String
Public Property PosBezeichnung As String
Public Property PosKostenart As Integer?
Public Property Datum As String
Public Property Material As Double?
Public Property GMK As Double?
Public Property Lohn As Double?
Public Property Menge As Integer?
Public Property Mengeneinheit As String
End Class
Public Class Arbeitsgaenge
Public Property Verkaufsartikel As String
Public Property AGNR As Integer?
Public Property Bereich As String
Public Property Lohn As Double?
Public Property Kostenstelle As Integer?
Public Property ARBPLATZ As String
End Class
Public Class RootObject
Public Property Artikelstammdaten As List(Of Artikelstammdaten)
Public Property Stueckliste As List(Of Stueckliste)
Public Property Arbeitsgaenge As List(Of Arbeitsgaenge)
End Class
Edit: I also changed the names from "ManufacturingCosts" and "MaterialCosts" to "Stueckliste" and "Arbeitsgaenge"
And here is my json-File:
{"Artikelstammdaten":[{"Artikel":"VAUBEF0010"},
{"BezeichnungDE":"Sammelbandantrieb"},
{"BezeichnungEN":"Collection belt drive N50"},
{"Einheit":"STK"},
{"MatGrp":"VAU"},
{"Kostenart": 1500},
{"Vertriebstext_DE": "Antrieb, Umlenkungen"},
{"Vertriebstext_EN": "Drive, Deflections"},
{"Stueckliste":"VAUBEF0010"},
{"Status":"F"},
{"Klasse":"VTPIMV"},
{"Mantelflaeche":1.3},
{"Gewicht":120},
{"KlasseID":"1.2.6.5"}],
"Stueckliste": [{"Verkaufsartikel":"VAUBEF0010"},
{"Position": 10},
{"PosArtikel":"Z0306251"},
{"PosBezeichnung":"VEL Elektro- Montagematerial"},
{"PosKostenart":9105},
{"Datum":"2022-01-31"},
{"Material":60.41},
{"GMK":3.63},
{"Lohn":2.07},
{"Menge":1},
{"Mengeneinheit":"STK"}],
"Arbeitsgaenge": [{"Verkaufsartikel":"VAUBEF0010"},
{"AGNR":10},
{"Bereich":"Mechanische Montage"},
{"Lohn":89.1},
{"Kostenstelle":523500},{"ARBPLATZ":"K950M"}]
}
What am i doing wrong?

Answer 1

I tried DeserializeObject with the json you provided
Public Class Artikelstammdaten
Public Property Artikel As String
Public Property BezeichnungDE As String
Public Property BezeichnungEN As String
Public Property Einheit As String
Public Property MatGrp As String
Public Property Kostenart As Integer
Public Property Vertriebstext_DE As String
Public Property Vertriebstext_EN As String
Public Property Stueckliste As String
Public Property Status As String
Public Property Klasse As String
Public Property Mantelflaeche As Double
Public Property Gewicht As Integer
Public Property KlasseID As String
End Class
Public Class ManufacturingCost
Public Property Verkaufsartikel As String
Public Property Position As Integer
Public Property PosArtikel As String
Public Property PosBezeichnung As String
Public Property PosKostenart As Integer
Public Property Datum As String
Public Property Material As Double
Public Property GMK As Double
Public Property Lohn As Double
Public Property Menge As Integer
Public Property Mengeneinheit As String
End Class
Public Class MaterialCost
Public Property Verkaufsartikel As String
Public Property AGNR As Integer
Public Property Bereich As String
Public Property Lohn As Double
Public Property Kostenstelle As Integer
Public Property ARBPLATZ As String
End Class
Public Class Root4
Public Property Artikelstammdaten As List(Of Artikelstammdaten)
Public Property ManufacturingCosts As List(Of ManufacturingCost)
Public Property MaterialCosts As List(Of MaterialCost)
End Class
Private Sub btnJson4_Click(sender As Object, e As EventArgs)
Dim Json As String = "{'Artikelstammdaten':[{'Artikel':'VAUBEF0010'},
{'BezeichnungDE':'Sammelbandantrieb'},
{'BezeichnungEN':'Collection belt drive N50'},
{'Einheit':'STK'},
{'MatGrp':'VAU'},
{'Kostenart': 1500},
{'Vertriebstext_DE': 'Antrieb, Umlenkungen'},
{'Vertriebstext_EN': 'Drive, Deflections'},
{'Stueckliste':'VAUBEF0010'},
{'Status':'F'},
{'Klasse':'VTPIMV'},
{'Mantelflaeche':1.3},
{'Gewicht':120},
{'KlasseID':'1.2.6.5'}],
'ManufacturingCosts': [{'Verkaufsartikel':'VAUBEF0010'},
{'Position': 10},
{'PosArtikel':'Z0306251'},
{'PosBezeichnung':'VEL Elektro- Montagematerial'},
{'PosKostenart':9105},
{'Datum':'2022-01-31'},
{'Material':60.41},
{'GMK':3.63},
{'Lohn':2.07},
{'Menge':1},
{'Mengeneinheit':'STK'}],
'MaterialCosts': [{'Verkaufsartikel':'VAUBEF0010'},
{'AGNR':10},
{'Bereich':'Mechanische Montage'},
{'Lohn':89.1},
{'Kostenstelle':523500},{'ARBPLATZ':'K950M'}]}"
Dim rt4 As New Root4
rt4 = JsonConvert.DeserializeObject(Of Root4)(Json)
Console.WriteLine(rt4.Artikelstammdaten(0).Artikel)
Console.WriteLine(rt4.Artikelstammdaten(1).BezeichnungDE)
End Sub
The json structure you provided and the clss you created are different.

Answer 2

Your problem is that your the values for the JSON properties "Artikelstammdaten", "Stueckliste" and "Arbeitsgaenge" are not objects. They are arrays of single-property objects. This can be seen if you reformat your JSON with e.g. https://jsonlint.com/:
{
"Artikelstammdaten": [{
"Artikel": "VAUBEF0010"
},
{
"BezeichnungDE": "Sammelbandantrieb"
},
{
"BezeichnungEN": "Collection belt drive N50"
},
{
"Einheit": "STK"
},
{
"MatGrp": "VAU"
},
{
"Kostenart": 1500
},
{
"Vertriebstext_DE": "Antrieb, Umlenkungen"
},
{
"Vertriebstext_EN": "Drive, Deflections"
},
{
"Stueckliste": "VAUBEF0010"
},
{
"Status": "F"
},
{
"Klasse": "VTPIMV"
},
{
"Mantelflaeche": 1.3
},
{
"Gewicht": 120
},
{
"KlasseID": "1.2.6.5"
}
],
"Stueckliste": [{
"Verkaufsartikel": "VAUBEF0010"
},
{
"Position": 10
},
{
"PosArtikel": "Z0306251"
},
{
"PosBezeichnung": "VEL Elektro- Montagematerial"
},
{
"PosKostenart": 9105
},
{
"Datum": "2022-01-31"
},
{
"Material": 60.41
},
{
"GMK": 3.63
},
{
"Lohn": 2.07
},
{
"Menge": 1
},
{
"Mengeneinheit": "STK"
}
],
"Arbeitsgaenge": [{
"Verkaufsartikel": "VAUBEF0010"
},
{
"AGNR": 10
},
{
"Bereich": "Mechanische Montage"
},
{
"Lohn": 89.1
},
{
"Kostenstelle": 523500
}, {
"ARBPLATZ": "K950M"
}
]
}
You would like to deserialize those arrays of single-property objects into c# models where each nested JSON property is bound to a model property. Since this is not implemented out of the box by Json.NET, you will need to create a custom generic JsonConverter such as the following:
Public Class ObjectToDictionaryArrayConverter(Of T)
Inherits JsonConverter
Public Overrides Function CanConvert(ByVal objectType As Type) As Boolean
Return objectType Is GetType(T)
End Function
Public Overrides ReadOnly Property CanWrite As Boolean
Get
Return False
End Get
End Property
Public Overrides Function ReadJson(ByVal reader As JsonReader, ByVal objectType As Type, ByVal existingValue As Object, ByVal serializer As JsonSerializer) As Object
If existingValue Is Nothing Then
Dim contract = serializer.ContractResolver.ResolveContract(objectType)
existingValue = contract.DefaultCreator()()
End If
Select Case JsonExtensions.MoveToContentAndAssert(reader).TokenType
Case JsonToken.StartArray
While JsonExtensions.ReadToContentAndAssert(reader).TokenType <> JsonToken.EndArray
Select Case reader.TokenType
Case JsonToken.StartObject
serializer.Populate(reader, existingValue)
Case Else
Throw New JsonSerializationException("Unexpected token type " & reader.TokenType.ToString())
End Select
End While
Case JsonToken.StartObject
serializer.Populate(reader, existingValue)
Case Else
Throw New JsonSerializationException("Unexpected token type " & reader.TokenType.ToString())
End Select
Return existingValue
End Function
Public Overrides Sub WriteJson(ByVal writer As JsonWriter, ByVal value As Object, ByVal serializer As JsonSerializer)
Throw New NotImplementedException()
End Sub
End Class
Public Module JsonExtensions
<System.Runtime.CompilerServices.Extension()>
Public Function ReadToContentAndAssert(ByVal reader As JsonReader) As JsonReader
Return JsonExtensions.ReadAndAssert(reader).MoveToContentAndAssert()
End Function
<System.Runtime.CompilerServices.Extension()>
Public Function MoveToContentAndAssert(ByVal reader As JsonReader) As JsonReader
If reader Is Nothing Then Throw New ArgumentNullException()
If reader.TokenType = JsonToken.None Then reader.ReadAndAssert() ' Skip past beginning of stream.
While reader.TokenType = JsonToken.Comment ' Skip past comments.
reader.ReadAndAssert()
End While
Return reader
End Function
<System.Runtime.CompilerServices.Extension()>
Public Function ReadAndAssert(ByVal reader As JsonReader) As JsonReader
If reader Is Nothing Then Throw New ArgumentNullException()
If Not reader.Read() Then Throw New JsonReaderException("Unexpected end of JSON stream.")
Return reader
End Function
End Module
Then modify your RootObject as follows, to replace the lists with single objects:
Public Class RootObject
Public Property Artikelstammdaten As Artikelstammdaten
Public Property Stueckliste As Stueckliste
Public Property Arbeitsgaenge As Arbeitsgaenge
End Class
And deserialize as follows:
Dim root as RootObject = Nothing
If OpenfilePath IsNot Nothing Then
Dim settings = New JsonSerializerSettings() With { .Converters = New JsonConverter() { _
New ObjectToDictionaryArrayConverter(Of Artikelstammdaten)(), _
New ObjectToDictionaryArrayConverter(Of Stueckliste)(), _
New ObjectToDictionaryArrayConverter(Of Arbeitsgaenge)() } }
Using fileReader = New StreamReader(OpenfilePath)
Using jsonReader = New JsonTextReader(fileReader)
root = JsonSerializer.CreateDefault(settings).Deserialize(Of RootObject)(jsonReader)
End Using
End Using
End If
Demo vb.net fiddle here.
Notes:
If you can modify your JSON format so that "Artikelstammdaten", "Stueckliste" and "Arbeitsgaenge" are objects rather than arrays of objects, the converter becomes unnecessary.
For performance reasons, Newtonsoft recommends reading directly from a file using a stream reader.
a StreamReader should always be closed via a Using statement after you are done reading from it.
I did not implement re-serialization of an object as an array of single-property objects because your question did not indicate it was necessary.
In c# ObjectToDictionaryArrayConverter<T> would be as follows:
public class ObjectToDictionaryArrayConverter<T> : JsonConverter
{
public override bool CanConvert(Type objectType) => objectType == typeof(T);
public override bool CanWrite => false;
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (existingValue == null)
{
var contract = serializer.ContractResolver.ResolveContract(objectType);
existingValue = contract.DefaultCreator();
}
switch (reader.MoveToContentAndAssert().TokenType)
{
case JsonToken.StartArray:
{
while (reader.ReadToContentAndAssert().TokenType != JsonToken.EndArray)
{
switch (reader.TokenType)
{
case JsonToken.StartObject:
serializer.Populate(reader, existingValue);
break;
default:
throw new JsonSerializationException("Unexpected token type " + reader.TokenType.ToString());
}
}
}
break;
case JsonToken.StartObject:
serializer.Populate(reader, existingValue);
break;
default:
throw new JsonSerializationException("Unexpected token type " + reader.TokenType.ToString());
}
return existingValue;
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) => throw new NotImplementedException();
}
public static partial class JsonExtensions
{
public static JsonReader ReadToContentAndAssert(this JsonReader reader) =>
reader.ReadAndAssert().MoveToContentAndAssert();
public static JsonReader MoveToContentAndAssert(this JsonReader reader)
{
if (reader == null)
throw new ArgumentNullException();
if (reader.TokenType == JsonToken.None) // Skip past beginning of stream.
reader.ReadAndAssert();
while (reader.TokenType == JsonToken.Comment) // Skip past comments.
reader.ReadAndAssert();
return reader;
}
public static JsonReader ReadAndAssert(this JsonReader reader)
{
if (reader == null)
throw new ArgumentNullException();
if (!reader.Read())
throw new JsonReaderException("Unexpected end of JSON stream.");
return reader;
}
}
c# demo fiddle here.