Custom Data Type for "HttpGet" Route in Asp.Net Web Api Project

Question

I try to add a variable of "custom data type" in my HttpGet Route.

I have this code:

[HttpGet("{idObject}")]
public ResponseSchema Get(ObjectId idObject)
{
    if (idObject == null) {
        throw new BodyParseException();
    }

    var user = _usersLogic.GetById(idObject);

    if (user == null) {
        _response.Success = false;
        _response.ErrorCode = "UserDoesNotExist";
    }
    else {
        _response.Objects.Add(user);
    }

    return _response;
}

ObjectId is a Datatype defined in using MongoDB.Bson.

For the Json Serialization and Deserialization we already have the code to automatically convert on both sides. But can this be similarly done in the Url itself.

We are right now using this Mvc version:

"Microsoft.AspNet.Mvc": "6.0.0-beta8"

So the URL looks like this:

GET Users/55b795827572761a08d735ac

The code to parse it from "string" to "ObjectId" is:

 ObjectId.TryParse(idString, out idObject);

The question is where to put that TryParse code. Because I need to tell ASP.NET how it should parse the idObject from String to ObjectId. Since the URL basically is a string.

For Post or Put JSON Payload I already found a solution. I know that this is something different. But Probably it is helpful to understand the scenario, or find a solution to this scenario:

public class EntityBaseDocument
{
    [JsonConverter(typeof(ObjectIdConverter))]
    public ObjectId Id { get; set; }
}

// Since we have this value converter. We can use ObjectId everywhere
public class ObjectIdConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        serializer.Serialize(writer, value.ToString());
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JToken token = JToken.Load(reader);
        return new ObjectId(token.ToObject<string>());
    }

    public override bool CanConvert(Type objectType)
    {
        return typeof(ObjectId).IsAssignableFrom(objectType);
    }
}

Answer 1

I believe NikoliaDante's answer works if you have a route such as /api/users?id={{idHere}}. However, if you are looking to have more RESTful routes, the solution below will do the trick for you. I just tested this out in a Web API 2 application and it works well. This will handle the use case where you may have a route such as /api/users/{{userId}}/something/{{somethingId}}.

//Http Parameter Binding Magic
public class ObjectIdParameterBinding : HttpParameterBinding
{
    public ObjectIdParameterBinding(HttpParameterDescriptor p) : base(p){ }

    public override Task ExecuteBindingAsync(System.Web.Http.Metadata.ModelMetadataProvider metadataProvider, HttpActionContext actionContext, System.Threading.CancellationToken cancellationToken)
    {
        var value = actionContext.ControllerContext.RouteData.Values[Descriptor.ParameterName].ToString();
        SetValue(actionContext, ObjectId.Parse(value));

        var tsc = new TaskCompletionSource<object>();
        tsc.SetResult(null);
        return tsc.Task;
    }
}

//Binding Attribute
public class ObjectIdRouteBinderAttribute : ParameterBindingAttribute
{
    public override HttpParameterBinding GetBinding(HttpParameterDescriptor parameter)
    {
        return new ObjectIdParameterBinding(parameter);
    }
}

//Controller Example
[Route("api/users/{id}")]
public async Task<User> Get([ObjectIdRouteBinder] ObjectId id) 
{
    //Yay!
}

Answer 2

ASP.NET Web API provides several approaches for do that. Take a look for Parameter Binding in Web API documentation.

Summary:

• FromUriAttribute - for simple DTO classes
• TypeConverter - to help Web API treat your class as simple type
• HttpParameterBinding - allow to create behaviour attribute
• ValueProvider - for more complex case
• IActionValueBinder - to write own parameter-binding process at all