Using Web API to read from SQL Server database that has related tables

I am trying to set up a Web API to be used for capturing the Clocking In and Clocking Out times of Employees after scanning a QR code.

I have set up this SQL Server database to test out the logic for Web API and IONIC 3 project.

My SQL Server code are as follows:

-- Creating table 1 'FarmWorker'
CREATE TABLE [dbo].[FarmWorker] 
(
    [FarmWorkerNum] int primary key identity(1,1),
    [FarmWorkerFName] varchar (15) not null,
    [FarmWorkerLName] varchar (15) not null,
    [FarmWorkerIDNum] char (13) not null
);
GO

-- Creating table 2 'AttendenceSheet'
CREATE TABLE [dbo].[AttendenceSheet] 
(
    [AttendenceSheetID] int primary key identity(1,1),
    [ClockInTime] datetime not null,
    [ClockOutTime] datetime not null,
    [FarmWorkerNum] int not null 
         FOREIGN KEY REFERENCES [FarmWorker](FarmWorkerNum)
);
GO

My Web API has been set up using Visual Studio 2015 and ASP.Net Web API 2.

My controller code for the Web API are as follows:

namespace AttendanceService.Controllers
{
    public class FarmWorkerController : ApiController
    {
        public IEnumerable<FarmWorker> Get()
        {
            using (AttDBEntities entities = new AttDBEntities())
            {
                 return entities.FarmWorkers.ToList();
            }
        }

        public FarmWorker Get(int id)
        {
            using (AttDBEntities entities = new AttDBEntities())
            {
                return entities.FarmWorkers.FirstOrDefault(e =>Convert.ToInt32(e.FarmWorkerIDNum) == id);
            }
        }
    }
}

When I run my Web API in the browser and attempt to run the first Get (to return a list of all FarmWorkers), I get the following error:

An error has occurred

System.InvalidOperationException: the 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'.

Type 'System.Data.Entity.DynamicProxies.FarmWorker_DA4B06B144222E86714953DE48C1952FFB 59C5CE216BAE8D8D506D8AEE9CEEBB' with data contract name 'FarmWorker_DA4B06B144222E86714953DE48C1952FFB59C5CE216BAE8D8D506D8AEE9CEEBB:htt p://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver if you are using DataContractSerializer or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to the serializer.

Does anyone know how to resolve this error? Any help will greatly be appreciated.

Thank you in advance.

[EDIT / UPDATE 1] - 2 hour after posting

I have managed to resolve the error message by adding in this code into the WebApiConfig.cs file:

config.Formatters.Remove(config.Formatters.XmlFormatter);
config.Formatters.Add(config.Formatters.JsonFormatter);

config.Formatters.JsonFormatter.SerializerSettings.Formatting = Newtonsoft.Json.Formatting.Indented;

QUESTION: Why do I receive an error when it is using XML format over JSON format? If possible, I would like to use the XML format, is there any way to make this possible ?

Thanks in advance again.