具有依赖项注入的ASP.NET WebApi模型绑定

Question

I have an web application that is written in ASP.NET MVC 5 with Razor views that works perfectly. I have a set of model classes that expects an ISomething in the constructor, and that ISomething is injected there using Unity. Everything works very nice.

I have the model class like this:

public class SecurityRoleModel : PlainBaseModel
{
    #region Constructor
    /// <summary>
    /// Initializes a new instance of the <see cref="SecurityRoleModel"/> class.
    /// </summary>
    /// <param name="encryptionLambdas">The encryption lambdas.</param>
    public SecurityRoleModel(IEncryptionLambdas encryptionLambdas)
    {
    }
    #endregion
}

In order to have the injection correctly working, I had to implement a custom DefaultModelBinder that takes care of the model constructor injection like this:

public class InjectableModelBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        if (modelType == typeof(PlainBaseModel) || modelType.IsSubclassOf(typeof(PlainBaseModel)))
            return DependencyResolver.Current.GetService(modelType);

        return base.CreateModel(controllerContext, bindingContext, modelType);
    }
}

Again, this is for the MVC part of the application, but now comes the ugly part: I have to implement a set of services (WebAPI) that deals with these models and I thought that I can do something similar to the MVC's DefaultModelBinder in WebAPI but it seems that is not as easy as I thought.

Now comes my question - though I've read (I think) a lot of posts regarding the implementation of custom IModelBinder (WebAPI), I cannot say that I found what I'm looking for; what I want is to find a way to not re-invent the wheel (to be read as "write a IModelBinder from scratch), I just want to have a place where the model class is instantiated and to have the possibility to put my code which gets the instance of the model class from the DI.

I hope I was clear enough. Thank you in advance.

Evdin

Answer 1

Though is not as broad as the MVC DefaultModelBinder and it covers only the situation when the serializer / deserializer is JSON.NET, the solution that I found for my issue is the following:

a) implement a custom version of CustomCreationConverter<T> from Newtonsoft.Json.Converters like this:

public class JsonPlainBaseModelCustomConverter<T> : CustomCreationConverter<T>
{
    public override T Create(Type objectType)
    {
        return (T)DependencyResolver.Current.GetService(objectType);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
            return null;

        return base.ReadJson(reader, objectType, existingValue, serializer);
    }
}

b) register the custom converter in the WebApiConfig class, Register method like this:

config.Formatters.JsonFormatter.SerializerSettings.Converters.Add(new JsonPlainBaseModelCustomConverter<PlainBaseModel>());

Though it might not be the optimal situation, it covers perfectly my issue.

If there is someone who knows a better solution, please let me know.

Thank you!