我第一次尝试使用MVC4，当我尝试创建控制器时，出现以下错误。请问有没有人能够指导我正确的方向？
Microsoft Visual Studio
System.Data.Entity.Edm.EdmAssociationEnd: ：在关系“PropertyData_DNISData”中，角色“PropertyData_DNISData_Target”的多重性无效。因为从属角色属性不是键属性，所以从属角色的上限必须为“*”。
public class PropertyData
{
[Key]
public virtual string PropertyID { get; set; }
[ForeignKey ("DNISData")]
public virtual string DNIS { get; set; }
public virtual string PropertyName { get; set; }
public virtual string PropertyGreeting { get; set; }
public virtual string PropertyOperator { get; set; }
public virtual string InvalidEntryPrompt { get; set; }
public virtual string NoEntryPrompt { get; set; }
public virtual string Comment { get; set; }
public virtual DNISData DNISData { get; set; }
}
public class DNISData
{
[Key]
public virtual string DNIS { get; set; }
[ForeignKey("PropertyData")]
public string PropertyID { get; set; }
public virtual string VDN { get; set; }
public virtual string PropertyGreeting { get; set; }
public virtual string Comment { get; set; }
public virtual PropertyData PropertyData { get; set; }
}
public class DigitData
{
[ForeignKey ("DNISData")]
[Key]
public virtual string DNIS { get; set; }
[Key]
public virtual string Digit { get; set; }
public virtual string InvalidEntryPrompt { get; set; }
public virtual DNISData DNISData { get; set; }
}