How would you handle validation errors in a REST API?

• Use model validation with data annotations.
• Return 400 Bad Request with a list of validation errors.

Example:

public class UserModel
{

[Required(ErrorMessage = "Email is required")]

[EmailAddress(ErrorMessage = "Invalid email format")]

public string Email { get; set; }

[Required]

[MinLength(6, ErrorMessage = "Password must be at least 6

characters")]

public string Password { get; set; }
}

// Controller action

[HttpPost("register")]

public IActionResult Register([FromBody] UserModel model)
{
if (!ModelState.IsValid)
{
var errors = ModelState.Values.SelectMany(v =>
v.Errors).Select(e => e.ErrorMessage);
return BadRequest(new { status = 400, error = "Validation
Failed", details = errors });
}
return Ok("User registered successfully");
}