ModelBinder attribute attached to a class has no effect (broken in rc2-final)

[AlekseyMartynov]

I have a model class and a binder:

[ModelBinder(BinderType = typeof(MyModelBinder))]
public class MyModel {
    public string Foo;
}

public class MyModelBinder : IModelBinder {

    public Task BindModelAsync(ModelBindingContext bindingContext) {
        var model = new MyModel {
            Foo = "Bar"
        };

        bindingContext.Result = ModelBindingResult.Success(bindingContext.ModelName, model);                               
        return Task.CompletedTask;
    }
}

Usage:

public IActionResult Index(MyModel model)
{
    return View();
}

In rc2, the binder isn't invoked, but the same approach works fine with classic MVC 5 and DNX rc1-final.
Full sample: https://github.com/AlekseyMartynov/aspnetcore-rc2-modelbinding

[dougbu]

I can reproduce this issue. The BinderTypeModelBinderProvider isn't called though the ModelBinderFactory has an instance first in its _providers -- as expected. Will see if I can reproduce this in the MVC Sandbox and debug further...

[dougbu]

🆒 bug 😎

Well BinderTypeModelBinderProvider is called but it's checking context.BindingInfo?.BinderType instead of context.Metadata.BinderType. At the top level, the first is non-null only when binding attributes are on the parameter. Binding attributes on a parameter type are not used.

Probably best for ModelBinderFactory to initialize DefaultModelBinderProviderContext.BindingInfo using both its own ModelBinderFactoryContext.BindingInfo and ModelBinderFactoryContext.Metadata.BindingInfo. No need for any changes except when initializing for the top level model.

This issue affects at least

• BinderTypeModelBinderProvider
• BodyModelBinderProvider
• HeaderModelBinderProvider
• ServicesModelBinderProvider

[Eilon]

Umm, and add a unit test? 😄

[dougbu]

@Eilon well I've fixed the bug while proving to myself I understood it. So why not 😺

[dougbu]

e63f094

[jruckert]

Is there a work around for this (if we want to keep using rc2-final)??

[AlekseyMartynov]

@jruckert yes, the workaround is to use the binder attribute explicitly (example)

[vaindil]

@dougbu I don't know if this is working. The attribute seems to have no effect in my code. Model binders are still called in order like normal, the attribute does nothing.

[HttpGet]
public async Task<IActionResult> Get([ModelBinder(BinderType = typeof(MyModelBinder))] int userId)
{
    // stuff
}

[dougbu]

@vaindil please open a new issue describing the exact scenario where you're seeing a regression of this fix.

I assume you are using an Mvc package more recent than 1.0.0. But, please include the project.json content in the new issue.