Return inherited DTO from API controller along with parent fields to the client

Question

I have a parent DTO as following:

public abstract class BaseDTO
{
   public list<string> message = new list<string>();
}

and a child class:

public class MyDTO : BaseDTO
{
   public string name { get; set; }
}

now when I try to view MyDTO in swagger schema section, the message field of BaseDTO does not appear in the list of fields also when I try to

return ok(MyDTO)

in my web api controller this field is not shown on client side

Answer 1

Install Microsoft.AspNetCore.Mvc.NewtonsoftJson Nuget Package, and add the following code in Program.cs:

builder.Services.AddMvc().AddNewtonsoftJson(options => {
    options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
});

Below is my test code, it works fine:

Model:

public class BaseDTO
{
    public List<string> message = new List<string>() { "test1","test2","test3" };
}

public class MyDTO : BaseDTO
{
    public string name { get; set; } 
}

Controller Action:

[HttpGet]
public IActionResult Test() 

    MyDTO myDTO = new MyDTO();
    myDTO.name = "name";

    return Ok(myDTO);
}

Test Result:

If you don't want to set value in BaseDTO, you can also set myDTO.message:

[HttpGet]
public IActionResult Test() 
{
    MyDTO myDTO = new MyDTO();
    myDTO.message.Add("test1");
    myDTO.message.Add("test2");
    myDTO.name = "name";

    return Ok(myDTO);
}