Entity Framework Core to Json Ignore ReferenceLoop - Parent Child

I having entity class with parent-child relationship that having problem serializing to json using newtonsoft json.net

public class Department
{        
    [Key]
    public int DepartmentId { get; set; }          
    public int? ParentId { get; set; }       
    public Department Parent { get; set; }          
    public ICollection<Department> Children { get; set; }
    public string Title { get; set; }
}

While i'm expecting a json format such as this.

[
  {
    "departmentId": 1,   
    "title":        "Finance",
    "children": [
      {
        "departmentId": 2,        
        "title":        "Accounting",
        "children": [
          {
            "departmentId": 3,            
            "title":        "Payable"
          }
        ]
      }
    ]
  }
]

But the result i get this Stackoverflow Exception from http-repl

I trying using Ignore ReferenceLooping, this doesn't solve the stackoverflow problem i have

services.AddMvc()
    .AddJsonOptions(options => {
       options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
    })

Here is the Controller, if you are asking;

//GET: api/Department
[HttpGet]
public async Task<ActionResult<IEnumerable<Department>>> GetDepartments()
{
    var result = await _context.Departments
        .Include(department => department.Children)
        .Where(department => department.ParentId == null)
        .ToListAsync();
    return Ok(result);
}

• Reference Loading Related Data with Include()
• Github commit a5d4a3d

I have tried Data Transfer Object (DTO) still not working.

Update 29 Dec 2018

Let set this up correctly, you can clone base project at https://github.com/wangkanai/Organization/tree/base. Then you can add the database in the following path src\Organization.WebApi

dotnet ef migrations add init
dotnet ef database update

This will give you at seed data for Department with following data

From the seed Data, the maximum child we will have only 3 level deep and no circle release as infinite loop.

• A > B > C

So we don't see A > B > A infinite loop here in this seed data.

After this we can doing debug using dotnet-httprepl and we should the same results.

Now lets comment out all methods in the department controller to limited the error scope. Then we get the http-repl up and running.

So let just enable get all departments and see what entity framework returns;

But this produce json serialization error for http-repl, maybe from swagger ui json http://localhost:56739/swagger/v1/swagger.json

Lets add \[JsonIgnore\] to the Site & Parent then rerun the http-repl

public class Department
{        
    [Key]
    public int DepartmentId { get; set; }
    [JsonIgnore]
    public int SiteId { get; set; }
    [JsonIgnore]
    public Site Site { get; set; }
    [JsonIgnore]
    public int? ParentId { get; set; }
    [JsonIgnore]
    public Department Parent { get; set; }          
    public ICollection<Department> Children { get; set; }
    public string Title { get; set; }
}

Still its produce the same error

So now let Ignore all relationship to serialize json to see if we can get all departments. But this produce departments without its children, which is not we are expecting the correct results.

public class Department
{        
    [Key]
    public int DepartmentId { get; set; }
    [JsonIgnore]
    public int SiteId { get; set; }
    [JsonIgnore]
    public Site Site { get; set; }
    [JsonIgnore]
    public int? ParentId { get; set; }
    [JsonIgnore]
    public Department Parent { get; set; }
    [JsonIgnore]
    public ICollection<Department> Children { get; set; }
    public string Title { get; set; }
}