MVC5 Referencing Guid

我正在创建这样一个表：

public class Team
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid Id { get; set; }
    public string CaptainId { get; set; }
    public string CoCaptainId { get; set; }
    public string ContactDetails { get; set; }
}

然后我有一张这样的表格：

public class TeamMember
{
    public string Id { get; set; }
    public string Description { get; set; }
    public string GameDisplayName { get; set; }
    public DateTime Joined { get; set; }
    public string TeamId { get; set; }
}

关于EF 6和MVC5，我有两个问题不理解。

1） 如何在团队表中引用我的Id字段。我是将TeamMember中的TeamId设置为字符串还是Guid？我知道我需要设置属性[ForeignKey("Team")]，但我仍然不知道如何在代码中正确引用它，因为每当我需要进行任何类型的比较时，我总是必须在Guid上键入.ToString()，才能获得与另一个字符串值进行比较的值。

2） 我的团队成员也有一个Id，这个Id引用了Identity框架中的User。我应该如何引用那个，Id应该是引用User表中Id的外键，但我也不知道如何正确引用那个，它是像我做的那样的字符串，还是Guid或其他什么？

编辑：

public class Team
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid Id { get; set; }
    public Guid CaptainId { get; set; }
    public Guid CoCaptainId { get; set; }
}
public class TeamMember
{
    public Guid MemberId { get; set; }
    public string TeamId { get; set; }
    public virtual Team Team { get; set; }
    public virtual Member Member { get; set; }
}
public class Member : IdentityUser
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string About { get; set; }
    public string Alias { get; set; }
    public string CustomUrl { get; set; }
    public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<Member> manager)
    {
        // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
        var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
        // Add custom user claims here
        return userIdentity;
    }
}
public class ApplicationDbContext : IdentityDbContext<Member>
{
    public ApplicationDbContext()
        : base("DefaultConnection")
    {
    }
    public DbSet<Team> Teams { get; set; }
    public DbSet<TeamMember> TeamMembers { get; set; }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<IdentityUserClaim>().ToTable("MemberClaim");
        modelBuilder.Entity<IdentityUserRole>().ToTable("MemberRole");
        modelBuilder.Entity<IdentityUserLogin>().ToTable("MemberLogin");
        modelBuilder.Entity<IdentityRole>().ToTable("Role");
        modelBuilder.Entity<Member>().ToTable("Member");
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
        modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
    }
    public static ApplicationDbContext Create()
    {
        return new ApplicationDbContext();
    }
}

我得到的错误：

var user = new Member { UserName = model.Email, Email = model.Email, CustomUrl = model.CustomUrl, Alias = model.Alias};
var team = new Team {CaptainId = user.Id, Created = currentTime, IsSingleMember = true};

CaptainId = user.Id gives an error:

Cannot convert source type 'string' to target type 'System.Guid'

public Guid TeamId { get; set; }

public class Team
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid Id { get; set; }
    public string CaptainId { get; set; }
    public string CoCaptainId { get; set; }
    public string ContactDetails { get; set; }
}
public class TeamMember
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid Id { get; set; }
    public string Description { get; set; }
    public string GameDisplayName { get; set; }
    public DateTime Joined { get; set; }
    public Guid TeamId { get; set; }
    public virtual Team Team { set; get; }
}