How to validate parameters coming in the request body

Question

I'm working on a api for my college assignment where me and two of my friends have to make a rather complex app. I know that there are a lot of things that can be done better, but it's not the point of the question. I have the following code for registering a new user:

app.MapPost("/register", async (RegistrationInput inp, ThreeMoronsContext db) =>
{
    var HashingResult = PasswordMegaHasher.HashPass(inp.password);
    try
    {
        User UserToRegister = new()
        {
            Id = Guid.NewGuid(),
            Login = inp.login,
            Password = HashingResult.hashpass,
            Salt = HashingResult.salt.ToString(),
            Name = inp.name,
            Surname = inp.surname,
            Patronymic = inp.patronymic,
            UserClassId = inp.UserClassId
        };
        await db.Users.AddAsync(UserToRegister);
        //await db.SaveChangesAsync();
        return Results.Ok(UserToRegister);
    }
    catch (Exception exc)
    {
        return TypedResults.BadRequest(exc.Message);
    }
});

ThreeMoronsContext is the DbContext that comes from EntityFrameworkCore. The RegistrationInput is:

    public record RegistrationInput(string login, string password, string name, string surname, string patronymic, int UserClassId)

I want to apply some validation to RegistrationInput, so that for example Login is between 5 and 20 characters long, the Name only cointains cyrillic letters and so on. I've tried applying [StringLength] and [RegularExpression], but i feel like i completely missunderstood the purpose of such attributes, since when i tried, for example, this input:

 "login": "s",
 "password": "hashme123",
 "name": "123",
 "surname": "s",
 "patronymic": "ss",
 "UserClassId": 1

i got a 200 response with a new user being being created:

{
  "id": "caf3796e-ba8d-4583-8c43-e69020a03353",
  "name": "123",
  "surname": "s",
  "patronymic": "ss",
  "login": "s",
  "password": "q6anLJxltC2Wf7443xRjwbOxCLZ5SXT9LdtSDOVceRk=",
  "userClassId": 1,
  "groups": [],
  "userClass": null,
  "salt": "System.Byte[]"
}

What should i do to apply validation to data coming from request body?

Answer 1

Follow my code :-

RegistrationInput.cs file (Model):-

public class RegistrationInput
{
 [Required]
 public string login { get; set; }
 [Required]
 public string password { get; set; }
 [Required]
 public string name { get; set; }
 [Required]
 public string surname { get; set; }
 public string patronymic { get; set; }
 [Required]
 public int UserClassId { get; set; }
}

Controller :-

app.MapPost("/register", async (RegistrationInput inp, ThreeMoronsContext db) =>
 {
 if (!ModelState.IsValid)
{
    return Results.BadRequest(ModelState);
}

var HashingResult = PasswordMegaHasher.HashPass(inp.password);
try
{
    User UserToRegister = new()
    {
        Id = Guid.NewGuid(),
        Login = inp.login,
        Password = HashingResult.hashpass,
        Salt = HashingResult.salt.ToString(),
        Name = inp.name,
        Surname = inp.surname,
        Patronymic = inp.patronymic,
        UserClassId = inp.UserClassId
    };
    await db.Users.AddAsync(UserToRegister);
    //await db.SaveChangesAsync();
    return Results.Ok(UserToRegister);
}
catch (Exception exc)
{
    return TypedResults.BadRequest(exc.Message);
}
});