根据特定条件在请求正文中反序列化接口 asp.net core

Question

我正在使用 ASP.Net Core 2.2 制作一个小型 Web 应用程序。

目前我只有一个界面：

public interface ILocation {

    public int Type {get;}
}

有2个类实现了这个ILocation接口：

public class StreetLocation: ILocation {

    public int Type {get;set;}

    public string City {get;set;}

    public string State {get;set;}
}

public class GeoCoordinateLocation: ILocation {

    public int Type {get;set;}

    public double Latitude{get;set;}

    public double Longitude{get;set;}
}

我有一个类StudentViewModel，用于接收从客户端发送到服务器的信息。该类实现如下：

public class StudentViewModel {

    public Guid Id {get;set;}

    public string Name {get;set;}

    public ILocation Address {get;set;}
}

我从客户端发出的请求是这样的：

{
    "id": "0da28089-c0da-41a7-a47f-89b54d52822b",
    "name": "Student 01",
    "location": {
        "type": 1,
        ...
    }
}

如果location type为1，ILocation将反序列化为StreetLocation，如果location type为2则反序列化为GeoCoordinateLocation。

请问有什么解决办法吗？ IModelBinder 在 asp.net core 中可以做到吗？

谢谢

Answer 1

您可以创建一个自定义 JsonConverter 来执行此操作。

1. 创建一个辅助函数来在运行时解析位置类型:Type ResolveILocationTypeRuntime(typeCode)
2. 创建一个辅助函数以在运行时创建某个特定类型的实例：DeserializeLocationRuntime(json, type)
3. 根据当前type读取Json或写入Json。

实施：

public class CustomLocationConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return true;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var json= JToken.ReadFrom(reader);
        var typeToken = json.SelectToken("type"); // or ??json.SelectToken("Type");
        if(typeToken ==null) return null;         //  
        var type= ResolveILocationTypeRuntime((int)typeToken);
        var location = DeserializeLocationRuntime(json, type);
        return location;
    }

    private Type ResolveILocationTypeRuntime(int type)
    {
        switch (type)
        {
            case 1:
                return typeof(StreetLocation);
            case 2:
                return typeof(GeoCoordinateLocation);
            default:
                throw new ArgumentOutOfRangeException("type should be 1|2");
        }
    }
    private ILocation DeserializeLocationRuntime(JToken json, Type locationType)
    {
        MethodInfo mi = typeof(JToken)
            .GetMethods(BindingFlags.Public | BindingFlags.Instance)
            .Where(m => m.Name == "ToObject" && m.GetParameters().Length == 0 && m.IsGenericMethod)
            .FirstOrDefault()
            ?.MakeGenericMethod(locationType);
        var location = mi?.Invoke(json, null);
        return (ILocation)location;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var location = value as ILocation;
        var type = ResolveILocationTypeRuntime(location.Type);
        serializer.Serialize(writer, location, type );
    }
}

并用JsonConverterAttribute 装饰您的Address 属性：

public class StudentViewModel
{
    public Guid Id { get; set; }
    public string Name { get; set; }

    [JsonProperty("location")]
    [JsonConverter(typeof(CustomLocationConverter))]

    public ILocation Address { get; set; }
}

测试用例：

控制器操作：

public IActionResult Test([FromBody]StudentViewModel model)
{
    return Json(model);
}

请求：

POST https://localhost:5001/home/test HTTP/1.1
Content-Type: application/json

{
    "id": "0da28089-c0da-41a7-a47f-89b54d52822b",
    "name": "Student 01",
    "location": {
        "type":2,
        "latitude": 1.2,
        "longitude":3.1415926,
    }
}