Error in XML result when applying hateoas to my web api

[.Net C Sharp Junior]

So i created a new web api project using .net framework.

first i created a class library project that has this link class below

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Access
{
public class Link
{
public string Href { get; set; }
public string Rel { get; set; }
public string Method { get; set; }

public Link(string href, string rel, string method)
{
this.Href = href;
this.Rel = rel;
this.Method = method;
}
}
}


And this is my table class Test the got generated when i added a .net ADO to connect to my sql server. The table has 2 fields and i added the link field by code

//------------------------------------------------------------------------------
// <auto-generated>
// This code was generated from a template.
//
// Manual changes to this file may cause unexpected behavior in your application.
// Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

namespace Access
{
using System;
using System.Collections.Generic;

public partial class Test
{
public int Id { get; set; }
public string Name { get; set; }

//added by code
public List<Link> Links { get; set; } = new
List<Link>();
}
}



Now i created a new controller

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using Access;

namespace Service.Controllers
{
public class Controller : ApiController
{

// GET api/Test
[Route("api/Test", Name = "GetAll")]
public IHttpActionResult GetAll()
{
using (TDBEntities entites = new
TDBEntities())
{
return Ok(entites.Test.ToList());
}
}

[Route("api")]
public IHttpActionResult GetApi()
{
List<Link> links = new List<Link>
{
new Link(Url.Link("GetAll",null),
"All","GET"),
};
API aPI = new API
{
Links = links
};
return Ok(aPI);

}


}

public class API
{
public List<Link> Links { get; set; } = new
List<Link>();
}
}


Now when i call the method GetApi from postman, i get a correct result from JSON

{
"Links": [
{
"Href": "https://localhost:1111/api/Test",
"Rel": "All",
"Method": "GET"
}
]
}



but when i switch to XML i get this error: How to solve this??

<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'.</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace />
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>Type 'Access.Link' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. See the Microsoft .NET Framework documentation for other supported types.</ExceptionMessage>
<ExceptionType>System.Runtime.Serialization.InvalidDataContractException</ExceptionType>
<StackTrace> at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.ThrowInvalidDataContractException(String message, Type type)
at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.CreateDataContract(Int32 id, RuntimeTypeHandle typeHandle, Type type)
at System.Runtime.Serialization.DataContract.DataContractCriticalHelper.GetDataContractSkipValidation(Int32 id, RuntimeTypeHandle typeHandle, Type type)
at System.Runtime.Serialization.XmlObjectSerializerContext.GetDataContract(Int32 id, RuntimeTypeHandle typeHandle)
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerialize(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle)
at WriteArrayOfLinkToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , CollectionDataContract )
at System.Runtime.Serialization.CollectionDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context)
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle)
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithoutXsiType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle)
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.InternalSerialize(XmlWriterDelegator xmlWriter, Object obj, Boolean isDeclaredType, Boolean writeXsiType, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle)
at WriteAPIDiscoveryToXml(XmlWriterDelegator , Object , XmlObjectSerializerWriteContext , ClassDataContract )
at System.Runtime.Serialization.ClassDataContract.WriteXmlValue(XmlWriterDelegator xmlWriter, Object obj, XmlObjectSerializerWriteContext context)
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.WriteDataContractValue(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle)
at System.Runtime.Serialization.XmlObjectSerializerWriteContext.SerializeWithoutXsiType(DataContract dataContract, XmlWriterDelegator xmlWriter, Object obj, RuntimeTypeHandle declaredTypeHandle)
at System.Runtime.Serialization.DataContractSerializer.InternalWriteObjectContent(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver)
at System.Runtime.Serialization.DataContractSerializer.InternalWriteObject(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver)
at System.Runtime.Serialization.XmlObjectSerializer.WriteObjectHandleExceptions(XmlWriterDelegator writer, Object graph, DataContractResolver dataContractResolver)
at System.Runtime.Serialization.DataContractSerializer.WriteObject(XmlWriter writer, Object graph)
at System.Net.Http.Formatting.XmlMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content)
at System.Net.Http.Formatting.XmlMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Web.Http.WebHost.HttpControllerHandler.&lt;WriteBufferedResponseContentAsync&gt;d__22.MoveNext()</StackTrace>
</InnerException>
</Error>

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