实体、循环或多个级联路径之间的实体框架关系

Question

我是 EF 的新手，正在尝试使用 Code First 设计我的数据库。以下是我的三个实体（我没有写完所有属性）。我有一个颂歌的情况。管理员不允许编辑费用，因此我必须创建另一个实体 (EditedExpense) 以将所有已编辑的费用保存在另一个表中。因此，当管理员尝试更改（编辑）费用并点击保存时，EditedExpense 中将创建一个新帖子。

public class Expense
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int ExpenseId { get; set; }

    [Required]
    public int CategoryId{ get; set; }
    [ForeignKey("CategoryId")]
    public virtual Category Category { get; set; }

    public virtual List<EditedExpense> EditedExpenses { get; set; }
}
public class EditedExpense
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int EditedExpenseId { get; set; }

    [Required]
    public int CategoryId{ get; set; }
    [ForeignKey("CategoryId")]
    public virtual Category Category { get; set; }

    public int ExpenseId { get; set; }

}
public class Category
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int CategoryId{ get; set; }

    public string Title

    public virtual List<Expense> Expenses { get; set; }
    public virtual List<EditedExpense> EditedExpenses { get; set; }
}

它会产生这个错误Introducing FOREIGN KEY constraint 'Expense_EditedExpenses' on table 'EditedExpense' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints

Answer 1

您需要关闭级联删除，在 Category 或 EditedExpenses 在 Expense 实体上执行此操作。

public class YourDbContext : DbContext
{
   // other code ommitted

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // Remove cascade delete from Category.
        modelBuilder.Entity<Expense>()
            .HasRequired(e => e.Category)
            .WithMany(c => c.Expenses)
            .WillCascadeOnDelete(false);

        // Or remove cascade delete from Edited Expense.
        //modelBuilder.Entity<Expense>()
        //    .HasMany(e => e.EditedExpenses)
        //    .WithRequired()
        //    .WillCascadeOnDelete(false);
    }
}

这是the explanation为什么不允许多级联。