C# ; } }

实际上，我不知道是否可以通过优雅的LINQ查询来实现。这是DFS的递归版本，它通过

ParentID

public static IEnumerable<TempTable> SortedList(IEnumerable<TempTable> list = null, int? ParentID = null, ILookup<int?, TempTable> lookup = null)
{
    if (lookup == null)
        lookup = list.ToLookup(x => x.ParentID, x => x);

    foreach (var p in lookup[ParentID].OrderBy(x => x.SortOrder))
    {
        yield return p;
        foreach (var c in SortedList(lookup: lookup, ParentID: p.ID))
            yield return c;
    }
}

公共静态IEnumerable-SortedList（IEnumerable-list=null，int？ParentID=null，ILookup-lookup=null）
{
如果（查找==null）
lookup=list.ToLookup（x=>x.ParentID，x=>x）；
foreach（查找[ParentID].OrderBy（x=>x.SortOrder）中的var p）
{
收益率p；
foreach（SortedList中的变量c（查找：查找，父ID:p.ID））
收益率c；
}
}

请查看我的编辑，不知道您是否收到了没有此评论的编辑通知。请查看我的编辑，不知道您是否收到了没有此评论的编辑通知。有多少深度？如果可以有无限的深度，那么在单个查询中是不可能的。实体框架的工作方式也是如此，它在递归性质的查询中失败。唯一的解决方案是树遍历。它可以有无限的深度，不应有任何限制。请修改您的代码，以便初始列表（在您的案例上下文中为.tentrables）可以是一个已经查询过的IEnumerable，并按要求传递和排序，因为您可能会注意到其他2个“新”答案（托马斯B.和罗曼·佩卡尔）这两种方案都有解决方案。您将如何做到这一点？谢谢您的时间。@RandRandom我已经添加了答案，它将对所有预加载的内容执行相同的工作。不确定在实体框架环境中是否需要查找，EF是否已经为主键/外键值提供了内置键搜索？如果是，则为n在什么情况下，在“正常”的基础上进行查找更好LINQ查询，或者如果您连续查询一个INT值使用查找，它更像是一个gernal的东西吗？嗯，这是一个更通用的解决方案，使用列表，而不是表，不能说实体框架中的内置键。因此，这里的查找有助于不迭代每个ID的整个列表。您可以解释一下为什么使用非递归版本吗？堆栈不是cau吗唱一首不必要的歌？默认（functionn调用）.NET应用程序的堆栈大小为4MB@64-点点滴滴1MB@32-位。此处使用的堆栈数据收集驻留在堆上，并受.NET对象堆大小限制2GB的限制。因此，对于非常深的层次结构，递归版本会在非递归版本之前抛出异常。此外：递归实现通常较慢由于调用开销（尽管如此：非递归更复杂，缺乏可读性）

ID = 1
ParentID = null
Name = Test 1
SortOrder = 1

ID = 2
ParentID = 1
Name = Test 2
SortOrder = 1

ID = 3
ParentID = 1
Name = Test 3
SortOrder = 2

ID = 4
ParentID = 2
Name = Test 4
SortOrder = 1

Test 1 //root element with sort order 1 = very top
Test 2 //child element of root with sort order 1
Test 4 //child element of test 2 with sort order 1
Test 3 //child element of root with sort order 2

from x in EntityModel.TempTables //DbSet<TempTable> by EntityFramework - which already holds all elements
   orderby x.SortOrder
   from y in x.TempTableChildren //Navigation Property by EntityFramework
   orderby y.SortOrder
   select y

ID = 193475037
ParentID = 2
Name = Test 192375937
SortOrder = 25

ID = 193475037
ParentID = 456798424
Name = Test 192375937
SortOrder = 4

public class LinqTestDemo
{
    Random rand = new Random();
    List<TempTable> list = new List<TempTable>();

    public List<TempTable> GetFlatData()
    {
        list = GetTestData();

        var rootElement = (from x in list
                            where x.ParentID == null
                            orderby x.SortOrder
                            select x).ToList();

        var flatList = OrderChilds(rootElement).ToList();

        foreach (var tempTable in flatList)
        {
            Console.WriteLine(string.Format("ID = {0} - ParentID = {1} - Name = {2} - SortOrder = {3}", tempTable.ID, tempTable.ParentID, tempTable.Name, tempTable.SortOrder));
        }

        return flatList;
    }

    private IEnumerable<TempTable> OrderChilds(List<TempTable> enumerable)
    {
        foreach (var tempTable in enumerable)
        {
            yield return tempTable;

            TempTable table = tempTable;
            var childs = OrderChilds((from x in list
                                        where x.ParentID == table.ID
                                        orderby x.SortOrder
                                        select x).ToList());

            foreach (var child in childs)
            {
                yield return child;
            }
        }
    }

    public List<TempTable> GetTestData()
    {
        var returnValue = new List<TempTable>();
        for (int i = 0; i < 50; i++)
        {
            var tempTable = new TempTable();
            tempTable.ID = i;
            if (i == 0)
                tempTable.ParentID = null;
            else
                tempTable.ParentID = rand.Next(0, i);

            var maxSortOrder = (from x in returnValue
                                where x.ParentID == tempTable.ParentID
                                select (int?)x.SortOrder).Max();

            if (maxSortOrder.HasValue)
                tempTable.SortOrder = maxSortOrder.Value + 1;
            else
                tempTable.SortOrder = 1;

            tempTable.Name = string.Format("Test {0:00}", i);
            returnValue.Add(tempTable);
        }

        return returnValue;
    }

    public class TempTable
    {
        public int ID { get; set; }
        public int? ParentID { get; set; }
        public string Name { get; set; }
        public int SortOrder { get; set; }
    }
}

public class Item
{
    public int ID { get; set; }
    public int? ParentID { get; set; }
    public string Name { get; set; }
    public int SortOrder { get; set; }
}

public void DoWork()
    {
        Item[] data = new Item[] {
            new Item() { ID = 2, ParentID = 1, Name = "Test 2", SortOrder = 1},
            new Item() { ID = 3, ParentID = 1, Name = "Test 3", SortOrder = 2},
            new Item() { ID = 4, ParentID = 2, Name = "Test 4", SortOrder = 1},
            new Item() { ID = 1, ParentID = null, Name = "Test 1", SortOrder = 1},
        };

        var result = from x in data
                     orderby x.SortOrder, x.ParentID
                     select x;

        foreach (var row in result.ToArray())
        {
            Console.WriteLine(row.Name);
        }
    }

public class TempTable
{
    public int ID {get;set;}
    public int? ParentID {get;set;}
    public String Name {get;set;}
    public int SortOrder {get;set;}
}

public List<TempTable> GetTempData()
{
    var temp = new List<TempTable>();
    temp.Add(new TempTable { ID = 1, ParentID = null, Name = "Test 1", SortOrder = 1 });
    temp.Add(new TempTable { ID = 2, ParentID = 1, Name = "Test 2", SortOrder = 1 });
    temp.Add(new TempTable { ID = 3, ParentID = 1, Name = "Test 3", SortOrder = 3 });
    temp.Add(new TempTable { ID = 4, ParentID = 2, Name = "Test 4", SortOrder = 1 });
    temp.Add(new TempTable { ID = 5, ParentID = 1, Name = "Test 5", SortOrder = 2 });
    return temp;
}

var data = GetTempData();
var result = data.OrderBy(d => d.SortOrder).ThenBy(d => d.ParentID);
//Do something with result

  public lEnumerable<TempTable> GetList( int? parentID = null){

     foreach ( var item in Context.TempTables
        .Where( x => x.ParentID == parentID )
        .OrderBy( x=> x.SortOrder)
        .ToList() {

        yield return item;

        foreach( var child in GetList( item.ID))
        {
            yield return child;
        }

     }
  }


  var sortedList = GetList();

 public IEnumerable<TempTable> PrepareList(IEnumerable<TempTable> list){
     list = list.OrderBy( x=> x.SortOrder);
     foreach(var item in list){
         yield return item;
         foreach(var child in PrepareList(item.ChildTempTables)){
             yield return child;
         }
     }
 }

 // since EF will automatically fill each children on fetch
 // all we need is just a top level nodes
 // which we will pass to PrepareList method
 var list = Context.TempTables.ToList().Where(x=> x.ParentID == null);
 var sortedList = PrepareList(list).ToList();

 // it is good to create list at the end if you are going to 
 // iterate it many times and logic will not change.

public static IEnumerable<TempTable> PreorderForest(IEnumerable<TempTable> list)
{
    var nodesByParent = list.GroupBy(x => x.ParentID.GetValueOrDefault(-1))
        .ToDictionary(xs => xs.Key, 
                      xs => xs.OrderBy(x => x.SortOrder).GetEnumerator());

    var stack = new Stack<IEnumerator<TempTable>>();
    stack.Push(nodesByParent[-1]);

    while (stack.Count > 0)
    {
        var nodes = stack.Peek();
        if (nodes.MoveNext())
        {
            yield return nodes.Current;
            IEnumerator<TempTable> children;
            if (nodesByParent.TryGetValue(nodes.Current.ID, out children))
                stack.Push(children);
        }
        else
            stack.Pop();
    }
}

public static IEnumerable<TempTable> SortedList(IEnumerable<TempTable> list = null, int? ParentID = null, ILookup<int?, TempTable> lookup = null)
{
    if (lookup == null)
        lookup = list.ToLookup(x => x.ParentID, x => x);

    foreach (var p in lookup[ParentID].OrderBy(x => x.SortOrder))
    {
        yield return p;
        foreach (var c in SortedList(lookup: lookup, ParentID: p.ID))
            yield return c;
    }
}