實體如何在父子關係中允許ForeignKey？

Question

我有實體

/// <summary> 
/// The greoup. 
/// </summary> 
public class Group 
{ 
    #region Public Properties 

    /// <summary> 
    /// Gets or sets the group id. 
    /// </summary> 
    [Key] 
    public int GroupId { get; set; } 

    /// <summary> 
    /// Gets or sets the parent group id. 
    /// </summary>  
    public int ParentGroupId { get; set; } 

    /// <summary> 
    /// Gets or sets the active. 
    /// </summary> 
    public int Active { get; set; } 

    /// <summary> 
    /// Gets or sets the description. 
    /// </summary> 
    public string Description { get; set; } 

    /// <summary> 
    /// Gets or sets the group guid. 
    /// </summary> 
    public Guid GroupGuid { get; set; } 

    /// <summary> 
    /// Gets or sets the order weight. 
    /// </summary> 
    public int OrderWeight { get; set; } 

    /// <summary> 
    /// Gets or sets the parent group. 
    /// </summary> 
    [ForeignKey("ParentGroupId")] 
    public virtual Group ParentGroup { get; set; } 

    /// <summary> 
    /// Gets or sets the groups. 
    /// </summary> 
    public virtual ICollection<Group> Groups { get; set; } 

    #endregion 
} 

我怎樣才能允許退出外鍵。因爲當我嘗試添加Group時，ParentGroupId = 0。我得到異常

無法確定依賴操作的有效順序。由於外鍵約束，模型要求或商店生成的值，可能會存在依存關係。

Answer 1

您正在使用此結構在數據庫中創建自引用表。所以ParentGroupId必須是空的。根節點不能有父節點，但由它產生的所有節點都會有父節點，所以需要使ParentGroupId爲空。