blocks|key|1328130|text|我想把我的答案贴出来，因为其他人都不帮我。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1328131|我的数据库有点不同，基本上我的表有一个ID和一个ParentID。该表是递归的。下面的代码获取所有子代，并将它们嵌套到最终列表中。|1328132|public+IEnumerable<Models.MCMessageCenterThread>+GetAllMessageCenterThreads(int+msgCtrId)
{
++++var+z+=+Db.MCMessageThreads.Where(t+=>+t.ID+==+msgCtrId)
++++++++.Select(t+=>+new+MCMessageCenterThread
++++++++{
++++++++++++Id+=+t.ID,
++++++++++++ParentId+=+t.ParentID+??+0,
++++++++++++Title+=+t.Title,
++++++++++++Body+=+t.Body
++++++++}).ToList();

++++foreach+(var+t+in+z)
++++{
++++++++t.Children+=+GetChildrenByParentId(t.Id);
++++}

++++return+z;
}

private+IEnumerable<MCMessageCenterThread>+GetChildrenByParentId(int+parentId)
{
++++var+children+=+new+List<MCMessageCenterThread>();

++++var+threads+=+Db.MCMessageThreads.Where(x+=>+x.ParentID+==+parentId);

++++foreach+(var+t+in+threads)
++++{
++++++++var+thread+=+new+MCMessageCenterThread
++++++++{
++++++++++++Id+=+t.ID,
++++++++++++ParentId+=+t.ParentID+??+0,
++++++++++++Title+=+t.Title,
++++++++++++Body+=+t.Body,
++++++++++++Children+=+GetChildrenByParentId(t.ID)
++++++++};

++++++++children.Add(thread);
++++}

++++return+children;
}|code-block|syntax|javascript|1328133|为了完整起见，下面是我的模型：|1328134|public+class+MCMessageCenterThread
{
++++public+int+Id+{+get;+set;+}
++++public+int+ParentId+{+get;+set;+}
++++public+string+Title+{+get;+set;+}
++++public+string+Body+{+get;+set;+}

++++public+IEnumerable<MCMessageCenterThread>+Children+{+get;+set;+}
}|1328135|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I wanted to post up my answer since the others didn't help me.

My database is a little different, basically my table has an ID and a ParentID. The table is recursive. The following code gets all children and nests them into a final list.

<pre><code>public IEnumerable&lt;Models.MCMessageCenterThread&gt; GetAllMessageCenterThreads(int msgCtrId)
{
 var z = Db.MCMessageThreads.Where(t =&gt; t.ID == msgCtrId)
 .Select(t =&gt; new MCMessageCenterThread
 {
 Id = t.ID,
 ParentId = t.ParentID ?? 0,
 Title = t.Title,
 Body = t.Body
 }).ToList();

 foreach (var t in z)
 {
 t.Children = GetChildrenByParentId(t.Id);
 }

 return z;
}

private IEnumerable&lt;MCMessageCenterThread&gt; GetChildrenByParentId(int parentId)
{
 var children = new List&lt;MCMessageCenterThread&gt;();

 var threads = Db.MCMessageThreads.Where(x =&gt; x.ParentID == parentId);

 foreach (var t in threads)
 {
 var thread = new MCMessageCenterThread
 {
 Id = t.ID,
 ParentId = t.ParentID ?? 0,
 Title = t.Title,
 Body = t.Body,
 Children = GetChildrenByParentId(t.ID)
 };

 children.Add(thread);
 }

 return children;
}
</code></pre>

For completeness, here's my model:

<pre><code>public class MCMessageCenterThread
{
 public int Id { get; set; }
 public int ParentId { get; set; }
 public string Title { get; set; }
 public string Body { get; set; }

 public IEnumerable&lt;MCMessageCenterThread&gt; Children { get; set; }
}
</code></pre>

blocks|key|1328223|text|作为加载子对象的示例，我将给出包含注释的comment对象的示例。每个注释都可能有一个子注释。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1328224|private+static+void+LoadComments(<yourObject>+q,+Context+yourContext)
{
++++if(null+==+q+%7C+null+==+yourContext)
++++{
++++++++return;
++++}
++++yourContext.Entry(q).Reference(x=>+x.Comment).Load();
++++Comment+curComment+=+q.Comment;
++++while(null+!=+curComment)
++++{
++++++++curComment+=+LoadChildComment(curComment,+yourContext);
++++}
}

private+static+Comment+LoadChildComment(Comment+c,+Context+yourContext)
{
++++if(null+==+c+%7C+null+==+yourContext)
++++{
++++++++return+null;
++++}
++++yourContext.Entry(c).Reference(x=>x.ChildComment).Load();
++++return+c.ChildComment;
}|code-block|syntax|javascript|1328225|现在，如果你有一个拥有自己集合的东西，你将需要使用Collection而不是Reference，并做同样的深入研究。至少这是我在处理Entity和SQLite时在这个场景中采用的方法。|1328226|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For an example of loading in child objects, I'll give the example of a Comment object that holds a comment. Each comment has a possible child comment.

<pre><code>private static void LoadComments(&lt;yourObject&gt; q, Context yourContext)
{
 if(null == q | null == yourContext)
 {
 return;
 }
 yourContext.Entry(q).Reference(x=&gt; x.Comment).Load();
 Comment curComment = q.Comment;
 while(null != curComment)
 {
 curComment = LoadChildComment(curComment, yourContext);
 }
}

private static Comment LoadChildComment(Comment c, Context yourContext)
{
 if(null == c | null == yourContext)
 {
 return null;
 }
 yourContext.Entry(c).Reference(x=&gt;x.ChildComment).Load();
 return c.ChildComment;
}
</code></pre>

Now if you were having something that has collections of itself you would need to use Collection instead of Reference and do the same sort of diving down. At least that's the approach I took in this scenario as we were dealing with Entity and SQLite.

blocks|key|1113166|text|这是一个古老的问题，但其他答案要么有n%2B1数据库的命中率，要么他们的模型有利于自下而上(树干到树叶)方法。在这种情况下，标签列表以树的形式加载，一个标签可以有多个父级。我使用的方法只有两次数据库命中:第一次是获取所选文章的标签，另一次是急切地加载连接表。因此，这使用了一种自顶向下(树叶到主干)的方法；如果您的连接表很大，或者如果结果不能真正缓存以供重用，那么急切地加载整个事情就会开始显示这种方法的权衡。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1113167|首先，我初始化了两个HashSet：一个用来保存根节点(结果集)，另一个用来保存对每个被“命中”的节点的引用。|offset|length|style|CODE|1113168|var+roots+=+new+HashSet<AncestralTagDto>();+//no+parents
var+allTags+=+new+HashSet<AncestralTagDto>();|code-block|syntax|javascript|1113169|接下来，我获取客户机请求的所有叶子，将它们放入一个对象中，该对象包含一个子集合(但在此步骤之后，该集合将保持为空)。|1113170|var+startingTags+=+await+_dataContext.ArticlesTags
++++++++.Include(p+=>+p.Tag.Parents)
++++++++.Where(t+=>+t.Article.CategoryId+==+categoryId)
++++++++.GroupBy(t+=>+t.Tag)
++++++++.ToListAsync()
++++++++.ContinueWith(resultTask+=>+
+++++++++++++resultTask.Result.Select(
++++++++++++++++++grouping+=>+new+AncestralTagDto(
++++++++++++++++++++++++grouping.Key.Id,+
++++++++++++++++++++++++grouping.Key.Name)));|1113171|现在，让我们获取标记自连接表，并将其全部加载到内存中：|1113172|var+tagRelations+=+await+_dataContext.TagsTags.Include(p+=>+p.ParentTag).ToListAsync();|1113173|现在，对于startingTags中的每个标记，将该标记添加到allTags集合，然后向下遍历树以递归获取祖先：|1113174|foreach+(var+tag+in+startingTags)
{
++++allTags.Add(tag);
++++GetParents(tag);
}
return+roots;|1113175|最后，下面是构建树的嵌套递归方法：|1113176|void+GetParents(AncestralTagDto+tag)
{
++++var+parents+=+tagRelations.Where(c+=>+c.ChildTagId+==+tag.Id).Select(p+=>+p.ParentTag);
++++if+(parents.Any())+//then+it's+not+a+root+tag;+keep+climbing+down
++++{
++++++++foreach+(var+parent+in+parents)
++++++++{
++++++++++++//have+we+already+seen+this+parent+tag+before?+If+not,+instantiate+the+dto.
++++++++++++var+parentDto+=+allTags.SingleOrDefault(i+=>+i.Id+==+parent.Id);
++++++++++++if+(parentDto+is+null)
++++++++++++{
++++++++++++++++parentDto+=+new+AncestralTagDto(parent.Id,+parent.Name);
++++++++++++++++allTags.Add(parentDto);
++++++++++++}

++++++++++++parentDto.Children.Add(tag);
++++++++++++GetParents(parentDto);
++++++++}
++++}
++++else+//the+tag+is+a+root+tag,+and+should+be+in+the+root+collection.+If+it's+not+in+there,+add+it.
++++{
++++++++//this+block+could+be+simplified+to+just+roots.Add(tag),+but+it's+left+this+way+for+other+logic.
++++++++var+existingRoot+=+roots.SingleOrDefault(i+=>+i.Equals(tag));
++++++++if+(existingRoot+is+null)
++++++++++++roots.Add(tag);
++++}
}|1113177|在幕后，我依靠HashSet的属性来防止重复。为此，重要的是您使用的中间对象(我在这里使用的是AncestralTagDto，它的子代集合也是一个HashSet)覆盖适合您的用例的Equals和GetHashCode方法。|1113178|entityMap^0|0|A|7|0|0|0|0|0|0|0|0|0|0|7|7|21|7|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@$D|18|E|19|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|1A|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1B|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|1C|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@]|A|$]]|$1|S|3|T|5|J|7|1E|8|@]|9|@]|A|$K|L]]|$1|U|3|V|5|6|7|1F|8|@]|9|@]|A|$]]|$1|W|3|X|5|J|7|1G|8|@]|9|@]|A|$K|L]]|$1|Y|3|Z|5|6|7|1H|8|@]|9|@]|A|$]]|$1|10|3|11|5|J|7|1I|8|@]|9|@]|A|$K|L]]|$1|12|3|13|5|6|7|1J|8|@$D|1K|E|1L|F|G]|$D|1M|E|1N|F|G]]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|15|$]]

This is an old question, but the other answers either had n+1 database hits or their models were conducive to bottom-up (trunk to leaves) approaches. In this scenario, a tag list is loaded as a tree, and a tag can have multiple parents. The approach I use only has two database hits: the first to get the tags for the selected articles, then another that eager loads a join table. Thus, this uses a top-down (leaves to trunk) approach; if your join table is large or if the result cannot really be cached for reuse, then eager loading the whole thing starts to show the tradeoffs with this approach.

To begin, I initialize two <code>HashSet</code>s: one to hold the root nodes (the resultset), and another to keep a reference to each node that has been "hit."

<pre><code>var roots = new HashSet&lt;AncestralTagDto&gt;(); //no parents
var allTags = new HashSet&lt;AncestralTagDto&gt;();
</code></pre>

Next, I grab all of the leaves that the client requested, placing them into an object that holds a collection of children (but that collection will remain empty after this step).

<pre><code>var startingTags = await _dataContext.ArticlesTags
 .Include(p =&gt; p.Tag.Parents)
 .Where(t =&gt; t.Article.CategoryId == categoryId)
 .GroupBy(t =&gt; t.Tag)
 .ToListAsync()
 .ContinueWith(resultTask =&gt; 
 resultTask.Result.Select(
 grouping =&gt; new AncestralTagDto(
 grouping.Key.Id, 
 grouping.Key.Name)));
</code></pre>

Now, let's grab the tag self-join table, and load it all into memory:

<pre><code>var tagRelations = await _dataContext.TagsTags.Include(p =&gt; p.ParentTag).ToListAsync();
</code></pre>

Now, for each tag in startingTags, add that tag to the allTags collection, then travel down the tree to get the ancestors recursively:

<pre><code>foreach (var tag in startingTags)
{
 allTags.Add(tag);
 GetParents(tag);
}
return roots;
</code></pre>

Lastly, here's the nested recursive method that builds the tree:

<pre><code>void GetParents(AncestralTagDto tag)
{
 var parents = tagRelations.Where(c =&gt; c.ChildTagId == tag.Id).Select(p =&gt; p.ParentTag);
 if (parents.Any()) //then it's not a root tag; keep climbing down
 {
 foreach (var parent in parents)
 {
 //have we already seen this parent tag before? If not, instantiate the dto.
 var parentDto = allTags.SingleOrDefault(i =&gt; i.Id == parent.Id);
 if (parentDto is null)
 {
 parentDto = new AncestralTagDto(parent.Id, parent.Name);
 allTags.Add(parentDto);
 }

 parentDto.Children.Add(tag);
 GetParents(parentDto);
 }
 }
 else //the tag is a root tag, and should be in the root collection. If it's not in there, add it.
 {
 //this block could be simplified to just roots.Add(tag), but it's left this way for other logic.
 var existingRoot = roots.SingleOrDefault(i =&gt; i.Equals(tag));
 if (existingRoot is null)
 roots.Add(tag);
 }
}
</code></pre>

Under the covers, I am relying on the properties of a <code>HashSet</code> to prevent duplicates. To that end, it's important that the intermediate object that you use (I used AncestralTagDto here, and its Children collection is also a <code>HashSet</code>), override the Equals and GetHashCode methods as appropriate for your use-case.

I have a tree structure in the DB with TreeNodes table. the table has nodeId, parentId and parameterId. in the EF, The structure is like TreeNode.Children where each child is a TreeNode...
I also have a Tree table with contain id,name and rootNodeId.

At the end of the day I would like to load the tree into a TreeView but I can't figure how to load it all at once.
I tried:

<pre><code>var trees = from t in context.TreeSet.Include("Root").Include("Root.Children").Include("Root.Children.Parameter")
 .Include("Root.Children.Children")
 where t.ID == id
 select t;
</code></pre>

This will get me the the first 2 generations but not more.
How do I load the entire tree with all generations and the additional data?

How to do recursive load with Entity framework?

数据库

SQLite

我在DB with TreeNodes表中有一个树形结构。该表包含nodeId、parentId和parameterId。在EF中，结构类似于TreeNode.Children，其中每个子对象都是一个TreeNode...我还有一个包含id、name和rootNodeId的树表。在一天结束的时候，我想把树加载到Tree...

问如何使用实体框架进行递归加载？
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