Web API参数绑定[Required]属性上的失败消息

Question

我有一个带有控制器方法的web api：

[Route("{player}/title(gameA)/appearance")]
public async Task<string> PutAppearance([ModelBinder]Player player, [FromBody] PlayerAppearance appearance){ //...stuff}

玩家外观如下所示：

 public class PlayerAppearance : PlayerAppearanceBase {///stuff}

和PlayerBase

    public abstract class PlayerAppearanceBase : IPlayerAppearance
{
    [Required]
    public string PlayerId { get; set; }

    public string TitleId{ get; set; }

当我发送一个请求时，请提出适当的请求：

{"PlayerId":"123456","LastModified":"0001-01-01T00:00:00","TitleId":"gameA"}

我收到以下错误：

"ModelState":{"appearance.PlayerId":["The PlayerId field is required."]}

现在我将控制器更改为如下所示：

public async Task<string> PutAppearance([ModelBinder]Player player)
    {
        var appearance =
            JsonConvert.DeserializeObject<PlayerAppearance>(Request.Content.ReadAsStringAsync().Result); 
///...}

一切正常。为什么它在简单的参数绑定方面会出现问题，但在直接反序列化时它可以正常工作。我失踪的幕后发生了什么？

*请注意，我已经从我的PlayerAppearance类中删除了无关的值