引入 FOREIGN KEY 约束可能会导致循环或多个级联路径 - 为什么? [英] Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths - why?

问题描述

我已经为此纠结了一段时间，但无法弄清楚发生了什么.我有一个包含 Sides(通常为 2)的 Card 实体 - Cards 和 Sides 都有一个 Stage.我正在使用 EF Codefirst 迁移，迁移失败并出现此错误:

I've been wrestling with this for a while and can't quite figure out what's happening. I have a Card entity which contains Sides (usually 2) - and both Cards and Sides have a Stage. I'm using EF Codefirst migrations and the migrations are failing with this error:

引入 FOREIGN KEY 约束 'FK_dbo.Sides_dbo.Cards_CardId' on表边"可能会导致循环或多个级联路径.指定开启DELETE NO ACTION 或 ON UPDATE NO ACTION，或修改其他 FOREIGN KEY约束.

Introducing FOREIGN KEY constraint 'FK_dbo.Sides_dbo.Cards_CardId' on table 'Sides' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.

这是我的卡片实体:

public class Card
{
    public Card()
    {
        Sides = new Collection<Side>();
        Stage = Stage.ONE;
    }

    [Key]
    [Required]
    public virtual int CardId { get; set; }

    [Required]
    public virtual Stage Stage { get; set; }

    [Required]
    [ForeignKey("CardId")]
    public virtual ICollection<Side> Sides { get; set; }
}

这是我的Side实体:

public class Side
{
    public Side()
    {
        Stage = Stage.ONE;
    }

    [Key]
    [Required]     
    public virtual int SideId { get; set; } 

    [Required]
    public virtual Stage Stage { get; set; }

    [Required]
    public int CardId { get; set; }

    [ForeignKey("CardId")]
    public virtual Card Card { get; set; }

}

这是我的 Stage 实体:

public class Stage
{
    // Zero
    public static readonly Stage ONE = new Stage(new TimeSpan(0, 0, 0), "ONE");
    // Ten seconds
    public static readonly Stage TWO = new Stage(new TimeSpan(0, 0, 10), "TWO");

    public static IEnumerable<Stage> Values
    {
        get
        {
            yield return ONE;
            yield return TWO;
        }

    }

    public int StageId { get; set; }
    private readonly TimeSpan span;
    public string Title { get; set; }

    Stage(TimeSpan span, string title)
    {
        this.span = span;
        this.Title = title;
    }

    public TimeSpan Span { get { return span; } }
}

奇怪的是，如果我将以下内容添加到我的 Stage 类中:

What's odd is that if I add the following to my Stage class:

    public int? SideId { get; set; }
    [ForeignKey("SideId")]
    public virtual Side Side { get; set; }

迁移运行成功.如果我打开 SSMS 并查看表格，我可以看到 Stage_StageId 已添加到 Cards(如预期/所需)，但是 Sides> 不包含对 Stage 的引用(不是预期的).

The migration runs successfully. If I open up SSMS and look at the tables, I can see that Stage_StageId has been added to Cards (as expected/desired), however Sides contains no reference to Stage (not expected).

如果我再添加

    [Required]
    [ForeignKey("StageId")]
    public virtual Stage Stage { get; set; }
    public int StageId { get; set; }

对于我的 Side 类，我看到 StageId 列添加到我的 Side 表中.

To my Side class, I see StageId column added to my Side table.

这是有效的，但现在在我的整个应用程序中，对 Stage 的任何引用都包含一个 SideId，这在某些情况下是完全不相关的.我只想给我的 Card 和 Side 实体一个基于上述 Stage 类的 Stage 属性而不污染舞台类如果可能，使用参考属性...我做错了什么?

This is working, but now throughout my application, any reference to Stage contains a SideId, which is in some cases totally irrelevant. I'd like to just give my Card and Side entities a Stage property based on the above Stage class without polluting the stage class with reference properties if possible... what am I doing wrong?

推荐答案

因为Stage是必需的，Stage的所有一对多关系代码> 将默认启用级联删除.这意味着，如果你删除一个 Stage 实体

Because Stage is required, all one-to-many relationships where Stage is involved will have cascading delete enabled by default. It means, if you delete a Stage entity

• 删除将直接级联到Side
• 删除将直接级联到 Card 并且因为 Card 和 Side 具有必需的一对多关系，通过以下方式启用级联删除再次默认它然后将从 Card 级联到 Side

• the delete will cascade directly to Side
• the delete will cascade directly to Card and because Card and Side have a required one-to-many relationship with cascading delete enabled by default again it will then cascade from Card to Side

因此，您有两个从 Stage 到 Side 的级联删除路径 - 这会导致异常.

So, you have two cascading delete paths from Stage to Side - which causes the exception.

您必须在至少一个实体中将 Stage 设为可选(即从 Stage 属性中删除 [Required] 属性) 或使用 Fluent API 禁用级联删除(无法使用数据注释):

You must either make the Stage optional in at least one of the entities (i.e. remove the [Required] attribute from the Stage properties) or disable cascading delete with Fluent API (not possible with data annotations):

modelBuilder.Entity<Card>()
    .HasRequired(c => c.Stage)
    .WithMany()
    .WillCascadeOnDelete(false);

modelBuilder.Entity<Side>()
    .HasRequired(s => s.Stage)
    .WithMany()
    .WillCascadeOnDelete(false);

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