MVC 5 Entity Framework 6 - 删除嵌套/分层数据

Question

我运行在处理分层数据并尝试删除具有子节点的节点时遇到了一些麻烦。

我建立了一个类似于this article的示例树，并用一点bootstrap装饰了ul-li项目（添加、删除和编辑图标）。

我现在正在为递归删除而苦苦挣扎，因为我使用的是 IEnumerable（Children），它是 parentNodeID 的逆结果。所以当删除一个节点时，子节点被更新并且系统抛出一个枚举错误（集合已经改变）。几年前我遇到过这样的错误，但我不记得我是如何修复它的。有什么建议吗？

这就是我得到的：

~/Models/Tree.cs

public class Tree
{
    [Key]
    public int NodeID { get; set; }

    [Display(Name ="Element name")]
    public string NodeName { get; set; }

    [Display(Name ="Element identifier")]
    public string NodeIdentifier { get; set; }

    public int? ParentNodeID { get; set; }
    public virtual Tree Parent { get; set; }
    public virtual ICollection<Tree> Children { get; set; }
}

~/Controllers/TreesController.cs

// Partial - only Delete Actions

// GET: Trees/Delete/5
public async Task<ActionResult> Delete(int? id)
{
    if (id == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
    }
    Tree tree = await db.Trees.FindAsync(id);
    if (tree == null)
    {
        return HttpNotFound();
    }

    if (tree.Children.Count > 0)
    {
        ViewBag.HasChildren = true;
    }
    else
    {
        ViewBag.HasChildren = false;
    }

    return View(tree);
}

// POST: Trees/Delete/5
[HttpPost, ActionName("Delete")]
[ValidateAntiForgeryToken]
public async Task<ActionResult> DeleteConfirmed(int id)
{
    Tree tree = await db.Trees.FindAsync(id);
    DeleteRecursive(tree);
    db.Trees.Remove(tree);
    await db.SaveChangesAsync();
    return RedirectToAction("Index");
}

public void DeleteRecursive(Tree tree)
{
    foreach(var child in tree.Children)
    {
        DeleteRecursive(child);
    }
    db.Trees.Remove(tree);
}

~/Views/Trees/Index.cshtml

<div class="container">
@helper BuildTree(IEnumerable<MVCMusicStore.Models.Tree> tree, int? parentID = null)
{
    var nodes = tree.Where(t => t.ParentNodeID == parentID).OrderBy(n => n.NodeIndexOrder);
    if (nodes.Any())
    {
        if (nodes.First().ParentNodeID == null)
        {
                <ul id="tree">
                    @foreach (var node in nodes)
                    {
                        <li>
                            @node.NodeIndexOrder - @node.NodeName &nbsp; <a href="@Url.Action("Edit","Trees",new { id = node.NodeID })" data-toggle="tooltip" data-placement="right" title="Bearbeiten"><i class="glyphicon glyphicon-edit"></i></a>&nbsp; <a href="@Url.Action("Delete","Trees",new { id = node.NodeID })" data-toggle="tooltip" data-placement="right" title="Löschen"><i class="glyphicon glyphicon-trash"></i></a>
                            @BuildTree(tree, node.NodeID)
                        </li>
                    }
                </ul>
        }
        else
        {
                <ul>
                    @foreach (var node in nodes)
                    {
                        <li>
                            @node.NodeIndexOrder - @node.NodeName &nbsp; <a href="@Url.Action("Edit","Trees",new { id = node.NodeID })" data-toggle="tooltip" data-placement="right" title="Bearbeiten"><i class="glyphicon glyphicon-edit"></i></a>&nbsp; <a href="@Url.Action("Delete","Trees",new { id = node.NodeID })" data-toggle="tooltip" data-placement="right" title="Löschen"><i class="glyphicon glyphicon-trash"></i></a>
                            @BuildTree(tree, node.NodeID)
                        </li>
                    }
                </ul>
        }         
    }
    else
    {

        <p>
            <a href="@Url.Action("Create","Trees", new { parentNodeID = parentID })" data-toggle="tooltip" data-placement="right" title="Neu"><i class="glyphicon glyphicon-plus"></i></a>
        </p>
    }
 }

@BuildTree(Model,null)
</div>

编辑 - 解决方案：

public void DeleteRecursive(Tree tree)
{
    foreach(var child in tree.Children.ToArray<Tree>())
    {
        DeleteRecursive(child);
    }
    db.Trees.Remove(tree);
}

使用数组进行删除不会改变原始集合。

Answer 1

public void DeleteRecursive(Tree tree)
{
    foreach(var child in tree.Children.ToArray<Tree>())
    {
        DeleteRecursive(child);
    }
    db.Trees.Remove(tree);
}

使用数组进行删除不会改变原始集合。

MVC 5 Entity Framework 6 - 删除嵌套/分层数据

MVC 5 Entity Framework 6 - deleting nested / hierarchical data

c#

recursion

entity-framework

hierarchical-data

asp.net-mvc-5