Produces Data Annotation

Question

I've been learning about Web API recently, and making plans to increase the scalability of my MVC apps, using it. When I finally got into creating a Web API controller, though, I discovered a [Produces("application/json")] annotation applied to the controller class. I haven't been able to figure out what that annotation does. I want the controller to only accept json input, so is this tag helpful to me?

Answer 1

The ProducesAnnotation only matters the response formatting. So this is not helpful for your need to restrict your input.

You can direct the content negotiation process to a specific type for the output of controller actions or a specific action by using ProducesAnnotation from the ASP.NET Core MVC framework. From the documentation (https://docs.asp.net/en/latest/mvc/models/formatting.html):

If you would like to restrict the response formats for a specific action you can, you can apply the [Produces] filter.

If you want to restrict inputs to json on a global level you could configure MVC on startup to have only a single InputFormatter of type JsonInputFormatter in your Startup.cs.

public void ConfigureServices(IServiceCollection services)
{
    ...    
    // Add framework services.
    services.AddMvc(config =>
    {
        // Add XML Content Negotiation
        config.RespectBrowserAcceptHeader = true;
        config.InputFormatters.Clear();
        config.InputFormatters.Add(new JsonInputFormatter());
    });
    ...
}

On Controller or Action level the counterpart of [Produces] is the [Consumes] Annotation. With

[Consumes("application/json")]
public class MyController : Controller
{
    public IActionResult MyAction([FromBody] CallModel model)
    {
        ....
    }
}

calls to this controller will only succeed if the client provides Content-Type header of application/json. Otherwise a 415 (Unsupported Media Type) will be returned.

Hope this helps.

Answer 2

Yes, the Produces attribute restricts the response to only the types defined. You can add more than one by using the attribute this way.

[Produces("application/json", "application/xml")]

ASP.NET Core uses a default value of JSON. If you want xml as well you will also have to specify the xml formatter in the ConfigureServices method.

services.AddMvc()
            .AddMvcOptions(o => o.OutputFormatters.Add(new XmlDataContractSerializerOutputFormatter()));