C
C#β€’2mo ago
Elio

βœ… JSON Deserialize Derived Class

Hi, i'm struggling to deserialize my object with the Newtonsoft.Json Librairy. I've a collection of Step named Steps which can be a Stepspecial or Stepnormal. I'm trying to write my JsonConverter to deserialize the collection of Step but when i try to deserialize i keep getting the stack overflow error because jObject.ToObject call back ReadJson :
public class StepConverterJSON : JsonConverter<Step>
{
#region Properties
public override bool CanWrite => false;
#endregion

#region Override Methods
public override void WriteJson(JsonWriter writer, Step? value, JsonSerializer serializer) { throw new NotImplementedException(); }

public override Step? ReadJson(JsonReader reader, Type objectType, Step? existingValue, bool hasExistingValue, JsonSerializer serializer)
{
// Load a JObject from the JsonReader
JObject jObject = JObject.Load(reader);

if(jObject["Message"] != null)
{
// Use the new serializer to deserialize the object
StepSpecial? stepSpecial = serializer.Deserialize<StepSpecial>(reader);
return stepSpecial;
}
else
{
StepNormal? stepNormal = jObject.ToObject<StepNormal>(serializer);
//StepNormal? stepNormal = serializer.Deserialize<StepNormal>(reader);
return stepNormal;
}
}
#endregion
}
public class StepConverterJSON : JsonConverter<Step>
{
#region Properties
public override bool CanWrite => false;
#endregion

#region Override Methods
public override void WriteJson(JsonWriter writer, Step? value, JsonSerializer serializer) { throw new NotImplementedException(); }

public override Step? ReadJson(JsonReader reader, Type objectType, Step? existingValue, bool hasExistingValue, JsonSerializer serializer)
{
// Load a JObject from the JsonReader
JObject jObject = JObject.Load(reader);

if(jObject["Message"] != null)
{
// Use the new serializer to deserialize the object
StepSpecial? stepSpecial = serializer.Deserialize<StepSpecial>(reader);
return stepSpecial;
}
else
{
StepNormal? stepNormal = jObject.ToObject<StepNormal>(serializer);
//StepNormal? stepNormal = serializer.Deserialize<StepNormal>(reader);
return stepNormal;
}
}
#endregion
}
Any idea how to solve this and write a good ReadJson method ? i've thought about the populate method but not sure this is the good way of doing it.
45 Replies
Elio
Elioβ€’2mo ago
Jimmacle
Jimmacleβ€’2mo ago
can you $paste the json?
MODiX
MODiXβ€’2mo ago
If your code is too long, you can post to https://paste.mod.gg/ and copy the link into chat for others to see your shared code!
Elio
Elioβ€’2mo ago
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Elio
Elioβ€’2mo ago
well it seem that i solved my problem just by adding this setting .... JsonSerializerSettings settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All }; but i do not really uderstand why and if it's the good solution
leowest
leowestβ€’2mo ago
you should avoid Newtonsoft unless you have an edge case that forces u to use it.
leowest
leowestβ€’2mo ago
System.Text.Json is the way to go these days.... with your data your modesl would look like this for STJ https://paste.mod.gg/wifpvbzpkwvj/0
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leowest
leowestβ€’2mo ago
var result = JsonSerializer.Deserialize<Width>(json);
var result = JsonSerializer.Deserialize<Width>(json);
no need to write any corverters either unless I missed out something from your json
Elio
Elioβ€’2mo ago
why do we avoid Newtonsoft ? thanks for the solution i'll try to do it this way
Jimmacle
Jimmacleβ€’2mo ago
it's pretty much obsolete with STJ and doesn't perform as well
leowest
leowestβ€’2mo ago
because its inefficient, slow, the same people that created newtonsoft made STJ
Elio
Elioβ€’2mo ago
Given the number of its popularity, I thought it was a good librairy
leowest
leowestβ€’2mo ago
newtonsoft was made in the acient era where there was no json reason reader and there was a wide range of dirty json in the market that needed handling
Elio
Elioβ€’2mo ago
ok good to know
leowest
leowestβ€’2mo ago
its popular because it existed when nothing existed so that is years until .net core came out
Elio
Elioβ€’2mo ago
do i really need to specify the name of each property for the json ?
leowest
leowestβ€’2mo ago
but the performances alone should speak for it self. u dont if they are the same except casing I do because if I need to change it later for whaterver reason I dont need to change the underlying variable name or vice-verse if the naming in the json
Elio
Elioβ€’2mo ago
i understand thanks i will quiclky try this and let u know if everything work well πŸ™‚
leowest
leowestβ€’2mo ago
I was trying to find the benchmark they did comparing both but I couldn't find lol
JC
JCβ€’2mo ago
If you're already deep into Newtonsoft with things like custom converters switching to STJ might not be trivial
Elio
Elioβ€’2mo ago
i've got the same problem as before, when i deserialize the array of step, it only use the class step and ignore the subclass stepspecial and stepnormal that's good i've started yesterday so i can still change from newton to STJ
JC
JCβ€’2mo ago
STJ can have some behavior thats unexpected, but generally reasonable. If you're serializing to an interface, only the members of that interface will be serialized.
Elio
Elioβ€’2mo ago
here is the good class : https://paste.mod.gg/pymisjadpkel/0
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Waffles from Human Resources
You should totally use the built in JSON class. Pretty sure someone else already said that tho
JC
JCβ€’2mo ago
I think the problem, as I understand it, is that you have Step[] as your target, but want to include derived classes as a part of the result
Elio
Elioβ€’2mo ago
yep that's it
JC
JCβ€’2mo ago
I don't know if that's something trivially done by System.Text.Json. If you try to deserialize to Step[], you're going to get an array of Step only.
Elio
Elioβ€’2mo ago
i want to have stepnormal and stepspecial instead of only step
No description
JC
JCβ€’2mo ago
Now, I'll assume you are not planning to allow typenamehandling
Elio
Elioβ€’2mo ago
yup and i can't really figure it out how to say to STJ to select the good class when i want to deserialize my object which contains this list
JC
JCβ€’2mo ago
JsonDerivedTypeAttribute would probably be what you're looking for, if .NET 7+ is your target
Jimmacle
Jimmacleβ€’2mo ago
it seems like the issue with this is the data itself, it does not include a type discriminator field
JC
JCβ€’2mo ago
You could take a look at https://github.com/dmitry-bym/JsonKnownTypes if you're going to stick with netwonsoft
GitHub
GitHub - dmitry-bym/JsonKnownTypes: Simple way to serialize and des...
Simple way to serialize and deserialize polymorphic types for Json.NET - dmitry-bym/JsonKnownTypes
Jimmacle
Jimmacleβ€’2mo ago
so you have to infer what C# type it is by the presence/absence of properties or simply make a single model with all the potential properties but marked optional
JC
JCβ€’2mo ago
but you probably want to add a descriminator field As far as your current converter is concerned take a look at changing StepSpecial? stepSpecial = serializer.Deserialize<StepSpecial>(reader); to StepSpecial? stepSpecial = jObject.ToObject<StepSpecial>(serializer);
Elio
Elioβ€’2mo ago
i'm open to switch to STJ, i just need to figure it out how to handle the desesrialization of my polymorphic object
Jimmacle
Jimmacleβ€’2mo ago
do you have control over the json schema?
JC
JCβ€’2mo ago
I think you're recursively entering the same serializer by trying to deserialize the derived type.
Elio
Elioβ€’2mo ago
what do you mean ? yup and with newtonsoft i've found the solution how to do it, rn i'm looking to find how to do it with STJ
Jimmacle
Jimmacleβ€’2mo ago
are you creating this json or is it coming from a program you can't change?
Elio
Elioβ€’2mo ago
y i'm creating the json
Elio
Elioβ€’2mo ago
to resume i want to save programbending as a json in order to export/import it from a usb
Jimmacle
Jimmacleβ€’2mo ago
do this
Elio
Elioβ€’2mo ago
perfect that was what i was looking for ! 😍 Well i should be careful about my vocabulary it would have save some time i think πŸ˜… polymorphic object/derived classes Thank you all for helping me !