System.NotSupportedException: Serialization and deserialization of 'System.Action' instances are not supported. Path: $.MoveNextAction

Question

I am following a simple tutorial on .NET 6 and it should work really simple, but apparently I get the exception. The sample code is the following:

public async Task<ServiceResponse<List<GetCharacterDto>>> GetAllCharacters()
{
    var response = new ServiceResponse<List<GetCharacterDto>>();
    var dbCharacters = await _context.Characters.ToListAsync();
    response.Data = dbCharacters.Select(c => _mapper.Map<GetCharacterDto>(c)).ToList();

    return response;
}

The code in GetCharacterDto is:

public class GetCharacterDto
{ 
    public int Id { get; set; }
    
    public string Name { get; set; } = "Frodo";

    public int HitPoints { get; set; } = 100;

    public int Strength { get; set; } = 10;

    public int Defense { get; set; } = 10;

    public int Intelligence { get; set; } = 10;

    public RpgClass Class { get; set; } = RpgClass.Knight;
}

RpgClass:

[JsonConverter(typeof(JsonStringEnumConverter))]
public enum RpgClass
{
    Knight = 1,
    Mage = 2,
    Cleric = 3
}

The exception

System.NotSupportedException: Serialization and deserialization of 'System.Action' instances are not supported. Path: $.MoveNextAction. Is thrown right at

var dbCharacters = await _context.Characters.ToListAsync(); 

If I call it synchronously

_context.Characters.ToList();

it works alright, but can't get it to work asynchronously.

I have both .NET 5 SDK and .NET 6 SDK installed, if that could be a potential issue.

Myrtia

RpgClass is an enum – Myrtia

the problem is not here ... you prolly have in controller results = GetAllCharacters(); return results; it would work with sync but will have this symptomps for async – Ruble

Answer 1

I was missing an await in the controller where I was calling the asynchronous GetAllCharacters() method.

Myrtia

yup that works for me – Subhead

Answer 2

[HttpGet("Info")]
[Authorize]
public async Task<ActionResult<UserDto>> GetCurrentUserInfo()
{
    var user = await _userService.GetCurrentUserInfo();
    return user.ToDto();
}

please remove ok and return directly

Danie

Answer 3

I found this problem when I had a task in a service without arguments, and I was trying to call it. When I added and argument it worked, but it's just a work-around. I think there's a better way to do it but I don't know what to do.

[HttpGet("Info")]
[Authorize]
public async Task<ActionResult<UserDto>> GetCurrentUserInfo()
{
    var user = await _userService.GetCurrentUserInfo();
    return Ok(user.ToDto());
}

I just added an argument and it worked

[HttpGet("Info")]
[Authorize]
public async Task<ActionResult<UserDto>> GetCurrentUserInfo()
{
    var user = await _userService.GetCurrentUserInfo("0");
    return Ok(user.ToDto());
}

Vitalize

I just realized that the method in the user Service and the controller method has the same name and when both method had the same signature that caused the : System.NotSupportedException: Serialization and deserialization of 'System.Action' instances are not supported. Path: $.MoveNextAction Just change the method name and it will be fixed if you have the same problem – Vitalize

Please edit, move the info from your comment into your answer and make sure that the whole thing is an answer to the question at the top of this page and according to How to Answer. And not, e.g. your experience with a similar but different problem and how you found a solution to that. Because that is the impression your post and comment currently give. – W

Answer 4

Had a similar problem, mistakenly I passed () => someMethod instead of someMethod as my MapGet handler.

Devitrify