C#•2mo ago

Support generic method NativeAOT JsonTypedInfo all together

Hello, I'm in the process of rewriting some of my libs to support native aot. But I have one use case for which I don't know how to do it. My use case look like this:

public interface IMyService
{
    T Get<T>();
}
public class MyService(bool useV1) : IMyService
{
    public T Get<T>()
    {
        return useV1
            ? GetA<T>()
            : GetB<T>();
    }

    private T GetA<T>()
    {
        string json = "{\"Data\": {\"Name\":\"Hello\", \"Id\":1 }}";
        return JsonSerializer.Deserialize<ModelA<T>>(json).Data;
    }

    private T GetB<T>()
    {
        string json = "{\"Data\": {\"Name\":\"World\", \"Id\":2 }}";
        return JsonSerializer.Deserialize<ModelB<T>>(json).Data;
    }
}

public class ModelA<T>
{
    public T Data { get; set; }
}
public class ModelB<T>
{
    public T Data { get; set; }
}

public interface IMyService
{
    T Get<T>();
}
public class MyService(bool useV1) : IMyService
{
    public T Get<T>()
    {
        return useV1
            ? GetA<T>()
            : GetB<T>();
    }

    private T GetA<T>()
    {
        string json = "{\"Data\": {\"Name\":\"Hello\", \"Id\":1 }}";
        return JsonSerializer.Deserialize<ModelA<T>>(json).Data;
    }

    private T GetB<T>()
    {
        string json = "{\"Data\": {\"Name\":\"World\", \"Id\":2 }}";
        return JsonSerializer.Deserialize<ModelB<T>>(json).Data;
    }
}

public class ModelA<T>
{
    public T Data { get; set; }
}
public class ModelB<T>
{
    public T Data { get; set; }
}

The issue is that JsonSerializer.Deserialize need either a JsonTypeInfo or a JsonSerializerOptions with TypeInfoResolver property set, to be working in NativeAot mode. But I don't know how to change IMyService without having to ask the user to provide two JsonTypeInfo parameters (One for ModelA<CustomData> and one for ModelB<CustiomData>) And using a JsonSerializerOptions would make the api less intuitive. Is there a way to JsonSourceGen only ModelA<> and ModelB<> in the lib and le the user provide the the T part? Any advice is welcome.

1 Reply

kalten•2mo ago

I found a solution by using a temporary JsonElement type

private T GetB<T>(JsonTypeInfo<T> jTypeInfo)
{
    string json = "{\"Data\": {\"Name\":\"World\", \"Id\":2 }}";
    JsonElement r = JsonSerializer.Deserialize(json, LibJsonContext.Default.ModelBT)!.Data;
    return SerializeUserModel<T>(r, jTypeInfo)!;
}

private T SerializeUserModel<T>(JsonElement jElement, JsonTypeInfo<T> jTypeInfo)
{
    return jElement.Deserialize<T>(jTypeInfo)!;
}

private T GetB<T>(JsonTypeInfo<T> jTypeInfo)
{
    string json = "{\"Data\": {\"Name\":\"World\", \"Id\":2 }}";
    JsonElement r = JsonSerializer.Deserialize(json, LibJsonContext.Default.ModelBT)!.Data;
    return SerializeUserModel<T>(r, jTypeInfo)!;
}

private T SerializeUserModel<T>(JsonElement jElement, JsonTypeInfo<T> jTypeInfo)
{
    return jElement.Deserialize<T>(jTypeInfo)!;
}

But not sure about the efficiency of it Using a Utf8JsonReader seem to work too

private T GetAA<T>(JsonTypeInfo<T> jTypeInfo)
{
    string json = "{\"Data\": {\"Name\":\"World\", \"Id\":2 }}";
    Utf8JsonReader reader = new(Encoding.UTF8.GetBytes(json));
    reader.Read();
    reader.Read();

    var propertyName = reader.GetString();
    if (propertyName != nameof(ModelA.Data))
        throw new Exception("Invalid property name");

    reader.Read();

    var data = JsonSerializer.Deserialize<T>(ref reader, jTypeInfo);

    return data;
}

private T GetAA<T>(JsonTypeInfo<T> jTypeInfo)
{
    string json = "{\"Data\": {\"Name\":\"World\", \"Id\":2 }}";
    Utf8JsonReader reader = new(Encoding.UTF8.GetBytes(json));
    reader.Read();
    reader.Read();

    var propertyName = reader.GetString();
    if (propertyName != nameof(ModelA.Data))
        throw new Exception("Invalid property name");

    reader.Read();

    var data = JsonSerializer.Deserialize<T>(ref reader, jTypeInfo);

    return data;
}

But Utf8JsonReader is not usable in an async context

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Support generic method NativeAOT JsonTypedInfo all together