ModelState.IsValid always true, regardless of DataAnnotations attributes

问题

I'm using the new MVC6 framework with Visual Studio 2015, and suddenly all my Data Annotations stopped working. All of them, without me changing the code.

public sealed class RegisterUser
{
    [Required(ErrorMessage = "required")]
    [RegularExpression(@"^((.|\n)*)$", ErrorMessage = "regex")]
    [StringLength(32, MinimumLength = 3, ErrorMessage = "length")]
    public string Name { get; set; }

    ...
}

And

[Route(Address + "/membership")]
public class MembershipController : Controller
{
    // POST [address]/membership/register
    [AllowAnonymous]
    [HttpPost("Register")]
    public IActionResult Register([FromBody]RegisterUser model)
    {
        // Validate the input model.
        if (model == null)
            return ...

        if (!ModelState.IsValid)
            return ... 

        // Always get HERE 
    }
}

Why, on earth, do I pass the "ModelState.IsValid" test (it always evaluates to true) ?

For example, I'm passing Name="x", and it still evaluates to true. As if the annotations aren't there.

Does it relate to using MvcCore ?

回答1:

Frustrating as it is, I forgot that changing to 'core' project strips out many of the common features. And so, in Startup.cs, add

• services.AddMvc()

or

• services.AddMvcCore().AddDataAnnotations()

Depending on your usage.

来源：https://stackoverflow.com/questions/38962288/modelstate-isvalid-always-true-regardless-of-dataannotations-attributes