@model DMDPace.DataAccess.DomainModels.User;
    @(Html.Kendo().Form<User>()
        .Name("User")
        .HtmlAttributes(new { action = "/Directory/User_Update", method = "POST" })
        .Layout("grid")
        .Grid(g => g.Cols(12).Gutter(20))
        .Items(i =>
            i.Add().Field(e => e.DepartmentId).Label("Отдел").Editor(e => e.DropDownList()
                .DataTextField("Name")
                .DataValueField("Id")
                .DataSource(s =>
                    s.Read(r => r.Action("GetDepartments", "Home"));

    public class User : Entity
        public int? DepartmentId { get; set; }
        public Department Department { get; set; }

public class Department : Entity
        public virtual List<User> Users { get; set; }
    }

services.AddControllers().AddNewtonsoftJson(options =>
                options.SerializerSettings.ContractResolver = new DefaultContractResolver();
                options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
            });

        [HttpGet("[controller]/User/{Id:int}")]
        public async Task<IActionResult> UserView(int id)
            var entity = await _userObjectService.GetAll()
                .Include(e => e.Department)
                .Where(e => e.Id == id)
                .FirstOrDefaultAsync();
            return View("User", entity);
        }
 
Telerik version - 2022.1.301.
                                            
Hello kva,

Thank you for applying code snippets.
However it is difficult for me to understand the full context of the behavior experienced on your side.
Could you please share additional details in regard to the experienced behavior like:
the circumstances in which the error occurs;
the full error code;
the full configuration of the shared files;
These or ideally an isolated sample project that showcases the behavior will enable me to investigate the issue in depth and suggest a possible solution.
Thank you for your cooperation in advance.
 
Regards,
 
Stoyan

 Progress Telerik
    
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Hello Kva,

I noticed you have updated your initial message with additional relevant information and snippets.

This allowed me to continue investigating the issue.
 
So far I wasn't able to reproduce the behavior on my side by using the shared snipepts. This leads me to suspect the issue is arises outside of Telerik UI for ASP.NET Core.

Here is what I recommend to resolve the behavior, if possible try replacing the NewtonSoft.Json Serializer with the AddJsonOptions built into the Microsoft.Extensions.DependencyInjection.
Alternatively, explore the suggestions in the related StackOverflow thread JSON.Net Self referencing loop detected.

If you find that I am missing something in the reproduction, please share more information on the topic or ideally, consider sharing an isolated sample project that showcases the reported behavior.

Regards,
Stoyan.