实体框架6.1.3非主键字段上的外键

Question

我有以下两个班级：

public class UserMembership: Entity
{
    public Guid Id { get; set; }
    public Guid UserGroupId { get; set; }
    public string LoginId { get; set; }
    public Guid SiteId { get; set; }

    public virtual Site Site { get; set; }
    public virtual SecurityUser SecurityUser { get; set; }
}

和

public class SecurityUser: Entity
{
    ICollection<UserMembership> _userMemberships = new Collection<UserMembership>();

    public Guid Id { get; set; }
    public string LoginId { get; set; }
    public string DisplayName { get; set; }
    public DateTimeOffset? LastLogOn { get; set; }
    public bool IsActive { get; set; }
    public bool IsServiceAccount { get; set; }
    public bool IsUserAccount { get; set; }

    public virtual ICollection<UserMembership> UserMemberships 
    {
        get { return _userMemberships; }
        set { _userMemberships = value; }
    }
}

想要使用LoginId字段而不是主键加入UserMembership和SecurityUser。这可能是使用Fluent API而不是属性吗？

以下是映射类：

public class SecurityUserMap : EntityMap<SecurityUser>
{
    public SecurityUserMap()
    {
        HasKey(p => p.Id);

        Property(p => p.LoginId)
            .HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute{ IsClustered = true, IsUnique = true }))
            .HasMaxLength(SecurityUserValidator.MaxLoginIdLength).IsRequired();
        Property(p => p.DisplayName)
            .HasMaxLength(SecurityUserValidator.MaxDisplayNameLength).IsRequired();

        Property(p => p.Modified)
            .HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute()));
    }
}

和

public class UserMembershipMap: EntityMap<UserMembership>
{
    public UserMembershipMap()
    {
        HasKey(p => p.Id);

        Property(p => p.UserGroupId)
            .HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute("UK_UserMembership", 1) { IsClustered = true, IsUnique = true }));
        Property(p => p.LoginId)
            .HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute("UK_UserMembership", 2) { IsClustered = true, IsUnique = true }))
            .HasMaxLength(UserMembershipValidator.MaxLoginIdLength).IsRequired();
        Property(p => p.SiteId)
            .HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute("UK_UserMembership", 3) { IsClustered = true, IsUnique = true }));

        Property(p => p.Modified)
            .HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute()));

        HasRequired(p => p.SecurityUser).WithMany(p => p.UserMemberships).Map(t => t.MapKey(new[] { "LoginId" }));
    }
}