OData $select and $expand not working on XML response?

Question

I have been developing an API with XML and JSON responses integrating OData, but I'm having a problem retrieving XML responses with OData $select and $expand methods, but other methods work fine like $top, $filter and $orderby etc... In JSON response everything works fine with OData methods.

This is the response Error

System.Runtime.Serialization.InvalidDataContractException: Type 'Microsoft.AspNetCore.OData.Query.Wrapper.SelectSome`1[Test_API.v2.Models.User]' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. Alternatively, you can ensure that the type is public and has a parameterless constructor - all public members of the type will then be serialized, and no attributes will be required.

This is my Program.cs

builder.Services.AddMvc(config =>

{  
    config.RespectBrowserAcceptHeader = true;  
    config.ReturnHttpNotAcceptable = true;  
    config.InputFormatters.Add(new XmlDataContractSerializerInputFormatter(config));  
    config.OutputFormatters.Add(new XmlDataContractSerializerOutputFormatter());  
    config.FormatterMappings.SetMediaTypeMappingForFormat("xml", MediaTypeHeaderValue.Parse("application/xml"));  
})  
    .AddOData(options => options.Select().Filter().OrderBy().Expand().OrderBy().Count().SetMaxTop(null));  

This is my User.cs

// <auto-generated> This file has been auto generated by EF Core Power Tools. </auto-generated>

#nullable disable  
using System;  
using System.Collections.Generic;  
using System.Runtime.Serialization;  
namespace Test_API.v2.Models  
{  
    public partial class User  
    {  
        public int UserId { get; set; }  
        public string Username { get; set; }  
        public string Email { get; set; }  
        public string Password { get; set; }  
        public virtual UserProfile Profile { get; set; }  
    }  
}  

This is my UserProfile.cs

// <auto-generated> This file has been auto generated by EF Core Power Tools. </auto-generated>

#nullable disable  
using System;  
using System.Collections.Generic;  
using System.Runtime.Serialization;  
namespace Test_API.v2.Models  
{  
    public partial class UserProfile  
    {  
        public UserProfile()  
        {  
            Users = new HashSet<User>();  
        }  
        public int ProfileId { get; set; }  
        public string ProfileName { get; set; }  
        public string Email { get; set; }  
        public virtual ICollection<User> Users { get; set; }  
    }  
}  

This is my Controller

[HttpGet]

[EnableQuery]  
[ProducesResponseType(typeof(IUser), 200)]  
public IQueryable<User> GetUser()  
{  
    return _context.Users.AsQueryable();  
}  

hoping anyone could help, been stuck in this for a month also I have been posting this on different community-based space websites but apparently, no one could help me find the solution.

please I really need help.

Answer 1

As stated before, xml is not a supported format for odata. You might be able to write middleware that converted request and response json to xml.

Note: your current middleware hack (xml formatter) will not work with odata iqueryable responses.