有没有办法在EF 6.0中定义备用键

Question

我有一个模型，需要为ClaimSet和AuthorizationStrategy生成唯一密钥：

public class ClaimSetResourceClaim {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ClaimSetResourceClaimActionAuthorizationStrategyOverrideId { get; set; }

    [Required]
    [Index(IsUnique = true, Order = 1)]
    public ClaimSet ClaimSet { get; set; }

    [Required]
    [Index(IsUnique = true, Order = 2)]
    public AuthorizationStrategy AuthorizationStrategy { get; set; }
}

public class ClaimSet {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ClaimSetResourceClaimActionAuthorizationId { get; set; }
    [StringLength(255)]
    public string RuleSetName { get; set; }
}

public class AuthorizationStrategy {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int AuthorizationStrategyId { get; set; }

    [StringLength(255)]
    [Required]
    public string DisplayName { get; set; }

    [StringLength(255)]
    [Required]
    public string AuthorizationStrategyName { get; set; }
}

。

modelBuilder.Entity<ClaimSetResourceClaim>().HasIndex(x => new { x.ClaimSet , x.AuthorizationStrategy }).IsUnique();

，但是在进行添加迁移时抛出错误，说序列不包含匹配元素。