How to post nested lists of IFormFile in .NET Core Web API?

Question

I am working to an ASP.NET Core Web API project (.NET 7.0). I am trying to build an endpoint to send data along with files. The Post controller action accepts an instance of the ParentDto class. This class contains a list of ChildDto, each one having a string value, a collection of IFormFile and an optional list of children of the same type.

public class ParentDto
{
    public int Id { get; set; }
    public List<ChildDto> Children { get; set; }
}

public class ChildDto
{
    public string? Value { get; set; }
    public List<IFormFile>? Files { get; set; }
    public List<ChildDto>? Children { get; set; }
}

[ApiController]
public class TestController : ControllerBase
{
    [HttpPost]
    public IActionResult Post([FromForm] ParentDto dto)
    {
        // Controller code...
    }
}

When I send data with Postman along with files, the Files property is populated only for the first level of the hierarchy. The children[0][children][0].files property is null, while all others are correctly populated. Even if I add more than one child to the ParentDto.Children property, the lists of files are handled correctly for each child. The problem seems to be in the nested list.

Answer 1

My postman picture like:

result: