Model Attribute binding in PUT Web API not wokring - ASP.NET Core 3.1 - rest

Question

I have a PUT Rest API that I want to do binding from both body and route parameters.
Code
[HttpPut("{Id}/someStuffApi")]
public ActionResult UpdateStatus([FromBody] StatusRequest StatusRequest)
{
// code ...
}
And the model class is
public class StatusRequest
{
[FromRoute(Name = "Id")]
[Required(ErrorMessage = "'Id' attribute is required.")]
public string Id { get; set; }
[FromBody]
[Required(ErrorMessage = "'Status' attribute is required.")]
public string Status { get; set; }
}
When I made a request to this API, the Id is not mapped to the model even though I added the FromRoute attribute explicitly. Any suggestions?

Answer 1

The [FromBody] model binding will effectively override the [FromRoute] option in your model class. This is by design (why, I'm not sure, but an MS decision). See the "[FromBody] attribute" section of this doc: https://learn.microsoft.com/en-us/aspnet/core/mvc/models/model-binding. As pointed out there: "When [FromBody] is applied to a complex type parameter, any binding source attributes applied to its properties are ignored." So adding the "[FromRoute]" attribute inside your model does nothing...it's ignored. You can remove both of those attributes from your model.
So the way around this is to put the route binding in the Put action as a method parameter and then manually add it to your model in the controller before using the model.
[HttpPut("{Id}/someStuffApi")]
public ActionResult UpdateStatus(int Id, [FromBody] StatusRequest StatusRequest)
{
StatusRequest.Id = Id;
// remaining code...
}
The downside to this method is that the Required attribute cannot remain on the Id parameter. It will be null at the time of model binding and if you have .Net Core 3.1 automatic model validation active, then that will always return a 422. So if you would have to manually check that yourself before adding it to the model.
If you want even more flexibility, you can look at something like the HybridModelBinding NuGet package that allows various combinations of model binding using attributes. But this is a 3rd party dependency that you may not want. (https://github.com/billbogaiv/hybrid-model-binding/)

Answer 2

You can use custom model binding,here is a demo:
TestModelBinderProvider:
public class TestModelBinderProvider : IModelBinderProvider
{
private readonly IList<IInputFormatter> formatters;
private readonly IHttpRequestStreamReaderFactory readerFactory;
public TestModelBinderProvider(IList<IInputFormatter> formatters, IHttpRequestStreamReaderFactory readerFactory)
{
this.formatters = formatters;
this.readerFactory = readerFactory;
}
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context.Metadata.ModelType == typeof(StatusRequest))
return new StatusBinder(formatters, readerFactory);
return null;
}
}
Startup.cs:
services.AddMvc()
.AddMvcOptions(options =>
{
IHttpRequestStreamReaderFactory readerFactory = services.BuildServiceProvider().GetRequiredService<IHttpRequestStreamReaderFactory>();
options.ModelBinderProviders.Insert(0, new TestModelBinderProvider(options.InputFormatters, readerFactory));
});
StatusBinder:
public class StatusBinder: IModelBinder
{
private BodyModelBinder defaultBinder;
public StatusBinder(IList<IInputFormatter> formatters, IHttpRequestStreamReaderFactory readerFactory)
{
defaultBinder = new BodyModelBinder(formatters, readerFactory);
}
public async Task BindModelAsync(ModelBindingContext bindingContext)
{
// callinng the default body binder
await defaultBinder.BindModelAsync(bindingContext);
if (bindingContext.Result.IsModelSet)
{
var data = bindingContext.Result.Model as StatusRequest;
if (data != null)
{
var value = bindingContext.ValueProvider.GetValue("Id").FirstValue;
data.Id = value.ToString();
bindingContext.Result = ModelBindingResult.Success(data);
}
}
}
}
StatusRequest:
public class StatusRequest
{
[Required(ErrorMessage = "'Id' attribute is required.")]
public string Id { get; set; }
[Required(ErrorMessage = "'Status' attribute is required.")]
public string Status { get; set; }
}
Action:
[HttpPut("{Id}/someStuffApi")]
public ActionResult UpdateStatus(StatusRequest StatusRequest)
{
return Ok();
}
result: