entity-framework – 实体类型没有键定义的EF6

public class Contacts
{
    [Key]
    public int ContactId { get; set; }
    public string Name { get; set; }
    public string Address { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string Zip { get; set; }
    [DataType(DataType.EmailAddress)]
    public string Email { get; set; }
}

我得到的错误是：

Entity Type ‘Contacts’ has no key defined. Define the key for this entity type.
Entity type: EntitySet ‘Contacts’ is based on type ‘Contacts’ that has no key defined