c# - Entity Framework : Dependencies due to foreign key constraints

Question

我一直在寻找解决方案，但找不到好的信息。很多 EF 文档已经过时了。这是我的问题。

如果我通过 ParentID 导航属性将 child 添加到 parent ，一切正常。

如果我通过 Children 列表将一个 child 添加到一个父对象，并且这个 child 已经存在，我会得到这个异常:

DbUpdateException: Unable to determine a valid ordering for dependent operations. Dependencies may exist due to foreign key constraints, model requirements, or store-generated values.

如果我通过 Children 列表将一个子项添加到父项并且该子项是新的(也需要持久化)，我会得到这个异常:

DbUpdateConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.

节点.cs

public class Node
{
  public long ID { get; private set; }
  public long? ParentID { get; set; }
  public List<Node> Children { get; set; }
}

相关的DbContext.cs

protected override void OnModelCreating(DbModelBuilder mb)
{
  mb.Entity<Node>()
    .HasMany(c => c.Children)
    .WithOptional()
    .HasForeignKey(c => c.ParentID);
}

Answer 1

你试过让你的 child 拥有属性(property)吗

public virtual ICollection<Node>而不是 List<Node>