Adjusting Default Parameter Attributes

WebApiClientCore executes requests and handles responses based on metadata. You can customize API method descriptions by applying desired attributes.

UseJsonFirstApiActionDescriptor

In modern web APIs, JSON is the most common request format, so client interfaces often need to submit JSON content.

The UseJsonFirstApiActionDescriptor behavior automatically applies JsonContentAttribute to complex parameter types for non-GET or HEAD requests.

services
    .AddWebApiClient()
    .UseJsonFirstApiActionDescriptor();

After configuration, the User parameter in the following interface will automatically have [JsonContent] applied:

public interface IUserApi
{
    [HttpPost("api/users")]
    Task<User> PostAsync(User user);  // No need to explicitly annotate [JsonContent]
}

Verifying Auto-Application

You can apply a custom ApiFilterAttribute subclass to IUserApi to observe the parameter attributes when calling PostAsync:

public class DebugFilterAttribute : ApiFilterAttribute
{
    public override Task OnRequestAsync(ApiRequestContext context)
    {
        var parameters = context.ActionDescriptor.Parameters;
        foreach (var param in parameters)
        {
            Console.WriteLine($"Parameter: {param.Name}");
            foreach (var attr in param.Attributes)
            {
                Console.WriteLine($"  Attribute: {attr.GetType().Name}");
            }
        }
        return Task.CompletedTask;
    }
}

You will see that JsonContentAttribute has been automatically added to the attribute collection.

When to Use

• Most APIs use JSON as the request body format
• You want to reduce repetitive [JsonContent] annotations
• Recommended for new projects by default