例外：外键约束可能导致多个循环答案

【问题标题】：Exception: Foreign Key Constraint may cause multiple cycles例外：外键约束可能导致多个循环
【发布时间】：2015-08-20 09:12:12
【问题描述】：

我是ASP .NET 的新手。我正在尝试使用以下模型进行简单的 CRUD。 Paper类中有三个ChartOfAccountIds，所以有三个Parent-Child关系。这些关系之一ChartOfAccountIdInventory 导致以下异常：

Introducing FOREIGN KEY constraint FK_dbo.Papers_dbo.ChartOfAccounts_ChartOfAccountIdInventory' on table 'Papers' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint.

ChartOfAccount 类：

public partial class ChartOfAccount
{
    public ChartOfAccount()
    {
        this.PapersSale = new HashSet<Paper>();
        this.PapersCostOfSale = new HashSet<Paper>();
        this.PapersInventory = new HashSet<Paper>();
    }

    [StringLength(50)]
    [ScaffoldColumn(true)]
    public string Id { get; set; }

    [StringLength(50)]
    public string Name { get; set; }

    public virtual ICollection<Paper> PapersSale { get; set; }
    public virtual ICollection<Paper> PapersCostOfSale { get; set; }
    public virtual ICollection<Paper> PapersInventory { get; set; }
}

论文类：

    public class Paper
    {
        [Key]
        [ScaffoldColumn(false)]
        public int Id { get; set; }

        [DisplayName("Name")]
        [Required(ErrorMessage = "Name is required")]
        [StringLength(50)]
        public string Name { get; set; }

        [DisplayName("Chart Of Account For Sale")]
        [Required(ErrorMessage = "Chart Of Account is required")]
        [StringLength(50)]
        public string ChartOfAccountIdSale { get; set; }

        [DisplayName("Chart Of Account For Inventory")]
        [Required(ErrorMessage = "Chart Of Account is required")]
        [StringLength(50)]
        public string ChartOfAccountIdInventory { get; set; }

        [DisplayName("Chart Of Account For Cost Of Sale")]
        [Required(ErrorMessage = "Chart Of Account is required")]
        [StringLength(50)]
        public string ChartOfAccountIdCostOfSale { get; set; }

        [ForeignKey("ChartOfAccountIdSale")]
        public virtual ChartOfAccount ChartOfAccountSale { get; set; }

        [ForeignKey("ChartOfAccountIdInventory")]
        public virtual ChartOfAccount ChartOfAccountInventory { get; set; }

        [ForeignKey("ChartOfAccountIdCostOfSale")]
        public virtual ChartOfAccount ChartOfAccountCostOfSale { get; set; }
   }

【问题讨论】：

标签： c# asp.net-mvc ef-code-first foreign-key-relationship

【解决方案1】：

你应该通过fluentApi设置“WillCascadeOnDelete = False”，像这样：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
         modelBuilder.Entity<Paper>()
            .HasRequired(c => c.ChartOfAccountSale )
            //.WithMany()
            .HasForeignKey(c => c.ChartOfAccountIdSale)
            .WillCascadeOnDelete(false);

         modelBuilder.Entity<Paper>()
            .HasRequired(c => c.ChartOfAccountInventory )
            //.WithMany()
            .HasForeignKey(c => c.ChartOfAccountIdInventory )
            .WillCascadeOnDelete(false);

         modelBuilder.Entity<Paper>()
            .HasRequired(c => c.ChartOfAccountCostOfSale )
            //.WithMany()
            .HasForeignKey(c => c.ChartOfAccountIdCostOfSale )
            .WillCascadeOnDelete(false);

}

【讨论】：

【解决方案2】：

我对所有 chartOfAccounts 都使用了 required 标签，这就是它出现异常的原因。

【讨论】：