C#•2y ago

✅ Complicated error with C# SignalR client

Hi, I'm trying to receive base class in signalr using

connection.on

connection.on

function. My base class has inherits and they all may be sent to the client.
Problem is in

connection.on<T>

connection.on<T>

method.
It converts whatever JSON serialized data comes to it straight to the

type, ignoring

's dervied types.
I have tested it by wrapping my

Foo

Foo

class in wrapper class

Bar

Bar

and passing it to the method:

c#
connection.On<Bar>(...)

c#
connection.On<Bar>(...)

This way, if I store

Baz: Foo

Baz: Foo

type in

Bar

Bar

and pass it to client, it will recieve

Bar

Bar

with

foo

foo

field having

Baz

Baz

type.

Is there a way to make

connection.on<T>

connection.on<T>

convert incoming data not just to

, but to it's derivative too without using wrapper classes?

Denis•1/5/24, 12:05 AM

Yes it is. https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/polymorphism?pivots=dotnet-8-0

How to serialize properties of derived classes with System.Text.Jso...

Learn how to serialize polymorphic objects while serializing to and deserializing from JSON in .NET.

Denis•1/5/24, 12:05 AM

What you need is a type discriminator

Denis•1/5/24, 12:06 AM

Alternatively, you could write a custom json converter, but that can get ugly very fast, if the only thing you need it for is type discrimination

VerdurOP•1/5/24, 12:57 AM

I have attribute on my base class, but

connection.on

connection.on

still refuses to convert data to the derived classes, it just stops converting at the type you passed in generic

Denis•1/5/24, 7:51 AM

And when serializing, each type inheriting your base has a $type json element?

DDenis Yes it is. https://learn.microsoft.com/en-us/dotnet/standard/serialization/syste...

Denis•1/5/24, 7:52 AM

I've recently faced the same issue and this helped me solve it

DDenis And when serializing, each type inheriting your base has a $type json element?

VerdurOP•1/5/24, 9:37 AM

Just checked it and looks like problem is in serializer indeed. It doesn't provide $type element if I'm serailizing base class, but if I serialize wrapper class that contains base class it does provide $type element

Denis•1/5/24, 11:01 AM

Consider the following hierarchy:

And the following collection:

Serializing the as is will produce this JSON:

Decorating the interface with:

....and serializing again shall produce the following result:

Denis•1/5/24, 11:04 AM

Are you using or something else?

Denis•1/5/24, 11:08 AM

I forgot to provide the code for serializing

VerdurOP•1/5/24, 12:09 PM

Yes, I'm using . There is no problem with manual serialization, but when I pass a value to signalr's function it doesn't serialize it's value with property

VerdurOP•1/5/24, 12:13 PM

Here's simple example to reproduce this bug:
Models:

Hub:

When I'm sending

foo

foo

, json serializator doesn't include property to json.
When I'm sending , json serializator includes property to json.

VerdurOP•1/5/24, 12:14 PM

I've checked it via WIreshark

VerdurOP•1/5/24, 12:23 PM

if I serialize and deserialize manually, then derived types are resolved properly

Denis•1/5/24, 12:46 PM

seems like a bug in signalr

https://github.com/dotnet/aspnetcore/issues/52342

GitHub

The JSON returned by SignalR does not contain the $type field · Iss...

Is there an existing issue for this? I have searched the existing issues Describe the bug When serializing descendant types, for methods that take a single (not a collection) parameter of the base ...

VerdurOP•1/5/24, 1:04 PM

Oh, thank you for sending a link, I was thinking about creating an issue myself

Denis•1/5/24, 1:09 PM

this kind of an issue is very unfortunate... Is it possible for you to ser/deser your self and send JSON directly via SignalR?

VerdurOP•1/5/24, 1:13 PM

Yes, I can do that or use wrapper type for now.

VerdurOP•1/5/24, 1:14 PM

Thank you for help, I think this problem is now resolved

Denis•1/5/24, 1:22 PM

$close

DDenis $close

MODiX•1/5/24, 1:22 PM

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