ReferenceLoopHandling.Ignore not working for Azure Mobile App Service to ignore serialization of circular references

Question

I'm using the following code in my startup class to prevent errors serializing my entities which may cause circular references, but it is not working.

Why?

public partial class Startup
    {
        public static void ConfigureMobileApp(IAppBuilder app)
        {

            HttpConfiguration config = new HttpConfiguration();

            new MobileAppConfiguration()
                .UseDefaultConfiguration()
                .ApplyTo(config);

            config.MapHttpAttributeRoutes();

            // Use Entity Framework Code First to create database tables based on your DbContext
            Database.SetInitializer(new MobileServiceInitializer());
            MobileAppSettingsDictionary settings = config.GetMobileAppSettingsProvider().GetMobileAppSettings();

            config.Formatters.JsonFormatter.SerializerSettings.Re‌​ferenceLoopHandling = ReferenceLoopHandling.Ignore;

            config.Services.Add(typeof(IExceptionLogger), new AiExceptionLogger());

            if (string.IsNullOrEmpty(settings.HostName))
            {
                app.UseAppServiceAuthentication(new AppServiceAuthenticationOptions
                {
                    // This middleware is intended to be used locally for debugging. By default, HostName will
                    // only have a value when running in an App Service application.
                    SigningKey = ConfigurationManager.AppSettings["SigningKey"],
                    ValidAudiences = new[] { ConfigurationManager.AppSettings["ValidAudience"] },
                    ValidIssuers = new[] { ConfigurationManager.AppSettings["ValidIssuer"] },
                    TokenHandler = config.GetAppServiceTokenHandler()
                });
            }

            app.UseWebApi(config);
        }
    }

Answer 1

According to your description, I created my Azure Mobile App project to test this issue. Based on your Startup.cs, I added my apiController as follows:

[MobileAppController]
public class ValuesController : ApiController
{
    [Route("api/values")]
    public HttpResponseMessage Get()
    {
        Department sales = new Department() { Name = "Sales" };
        Employee alice = new Employee() { Name = "Alice", Department = sales };
        sales.Manager = alice;
        return Request.CreateResponse(sales);
    }
}

public class Employee
{
    public string Name { get; set; }
    //[JsonIgnore]
    public Department Department { get; set; }
}

public class Department
{
    public string Name { get; set; }
    public Employee Manager { get; set; }
}

When access this endpoint, I encountered the following XML Circular Object References error:

Note: For a simple way, I removed the XML Formatter via config.Formatters.Remove(config.Formatters.XmlFormatter);. Also, you could refer to the section about preserving object references in XML from Handling Circular Object References.

After I removed XML Formatter, then I encountered the following error about object references loop in JSON:

Then, I followed this Loop Reference handling in Web API code sample, but without luck in the end. Also, I tried to create a new Web API project and found that ReferenceLoopHandling.Ignore could work as expected.

In the end, I found that if I remove the MobileAppController attribute from my apiController, then it could work as follows:

In summary, I assumed that you could try to ignore the reference attributes with the JsonIgnore for JSON.NET, for more details you could refer to fix 3:Ignore and preserve reference attributes.