未标记为“[DataMember（IsRequired = true）]”的属性不是通过JSON发送的

Here's my code:

这是我的代码：

[DataContract]
public class SideDto
{
    public SideDto() { }

    public SideDto(Side side)
    {
        SideId = side.SideId;
        Stage = side.Stage;
    }

    [Key]
    [DataMember(IsRequired = true)]
    public int SideId { get; set; }

    public Stage Stage { get; set; }

}
[DataContract]
pub