Read from File with multiple derived classes

Hi,

I’m using your library primarily for supporting serialization and deserialization of polymorphic objects. I have a base class “DataSetBase” and two deriving classes, “DataSet” and “BlackoutDataSet”. Following the serialization:

JsonSerializerOptions options = new JsonSerializerOptions().SetupExtensions();
DiscriminatorConventionRegistry registry = options.GetDiscriminatorConventionRegistry();
registry.RegisterType<DataSet>();
registry.RegisterType<BlackoutDataSet>();

using (var fileWriter = new StreamWriter(_failureFolderPath + GetFailureFileName(), true)){
	if (dataSet is DataSet)
	{
		jsonString = JsonSerializer.Serialize<DataSetBase>((DataSet)dataSet, options);
	}
	else if (dataSet is BlackoutDataSet)
	{
		jsonString = JsonSerializer.Serialize<DataSetBase>((BlackoutDataSet)dataSet, options);
	}
	else
	{
		throw Exception("Got unknown type");
	}

	if (jsonString != "")
		fileWriter.WriteLine(jsonString);
}

How can I be sure of the type of the object when deserializing?

ReadOnlySpan<byte> jsonReadOnlySpan = File.ReadAllBytes(_failureFolderPath + GetFailureFileName());
var reader = new Utf8JsonReader(jsonReadOnlySpan);
while (reader.Read()){
	var deserializedObject = JsonSerializer.Deserialize<????>(reader, options);
}

[mcatanzariti]

Don’t forget to setup a discriminator on each inherited class. You can decorate the class with JsonDiscriminatorAttribute or use ObjectMapping<T>.SetDiscriminator method.

Then you have to register your class in the discriminator registry.

For further details, see https://github.com/dahomey-technologies/Dahomey.Json/blob/master/README.md#polymorphism

Don’t hesitate to reopen if you have any problem.

[DeckardCain2014]

StreamReader was the solution. Thanks!