C# 遞歸構造樹狀數據結構（泛型），如何構造？如何查詢？

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首先，我們需要准備一張表，如下范例：

create table TreeTable
(
TreeId varchar(100) not null primary key,
NodeName nvarchar(50),--名稱
FatherTreeId varchar(100),--父親Id
)

為了節約時間，我直接沿用項目中的數據，作如下批量插入：

insert into TreeTable(TreeId,NodeName,FatherTreeId)
select [SpClassifyId],[ClassifyName],[ParentClassifyId]
from [dbo].[SM_SupplierClassify] 
where [ForefatherClassifyName] in('工程類','精裝修類','設計類','營銷類')

插入的數據，如下所示：

從上圖，我們可以看出，這些數據中有四種大類，分別為：('工程類','精裝修類','設計類','營銷類')，層級關系通過FatherTreeId構造，當然，此表中的層次不僅僅只有兩級，理論上支持N級，類似這種結構的數據現實生活中有很多，如：家譜，人員組織架構，營銷模式（微信的吸粉，病毒式營銷），甚至傳銷模式等等

那么，我們如何將上述數據轉變為樹狀結構的數據類型呢？

大家都會想到遞歸，但如何遞歸呢？

兩種方法，

一、如何構造：

1、遞歸式查詢，從根節點入手，查詢多次（效率非常低，在此不作介紹）

2、一次性查詢出所有數據，根據FatherTreeId，遞歸式查詢泛型（效率高。只查詢一次即可）我們介紹此種方法：

 首先，我們構造如下Model

    /// <summary>
    /// 我們要構造的樹
    /// </summary>
    public class TreeModel
    {
        public TreeModel()
        {
            children = new List<TreeModel>();
        }
        public string title { get; set; }
        public string value { get; set; }
        public string key { get; set; }
        public List<TreeModel> children { get; set; }

        public static TreeModel MakeTree(TreeTableModel supplierClassifyModels)
        {
            TreeModel Tree = new TreeModel();
            Tree.title = supplierClassifyModels.NodeName;
            Tree.key = supplierClassifyModels.TreeId;
            Tree.value = supplierClassifyModels.TreeId;
            if (supplierClassifyModels.children != null)
            {
                foreach (var item in supplierClassifyModels.children)
                {
                    Tree.children.Add(MakeTree(item));
                }
            }
            return Tree;
        }
    }
    

    /// <summary>
    /// 數據庫表對應的實體Model
    /// </summary>
    public class TreeTableModel
    {
        public TreeTableModel()
        {
            children = new List<TreeTableModel>();
        }
        public string TreeId { get; set; }
        public string NodeName { get; set; }
        public string FatherTreeId { get; set; }
        //子數據
        public List<TreeTableModel> children { get; set; }
    }

上述的TreeModel中的 MakeTree 方法用於遞歸構造樹！~_~ 重點

構造方法如下：

        /// <summary>
        /// 構造樹
        /// </summary>
        /// <returns></returns>
        public static BaseResponse<List<TreeModel>> BuildTree()
        {
            using (AnFuDBEntities context = new AnFuDBEntities())
            {
                List<TreeModel> TreeList = new List<TreeModel>();
                var data = context.TreeTable.ToList();
                var list = new List<TreeTableModel>();
                list = Mapper.DynamicMap<List<TreeTableModel>>(data);
                List<TreeTableModel> TreeModels = BuildTreeModel(list, string.Empty);
                foreach (var item in TreeModels)
                {
                    var Tree = TreeModel.MakeTree(item);
                    TreeList.Add(Tree);
                }
                var result = TreeList;
                return CommonBaseResponse.SetResponse<List<TreeModel>>(result, true);
            }
        }

        /// <summary>
        /// 遞歸方法，構造樹狀泛型
        /// </summary>
        /// <param name="AllList"></param>
        /// <param name="ParentClassifyId"></param>
        /// <returns></returns>
        private static List<TreeTableModel> BuildTreeModel(List<TreeTableModel> AllList, string ParentClassifyId)
        {
            List<TreeTableModel> List = new List<TreeTableModel>();

            if (!string.IsNullOrEmpty(ParentClassifyId))
            {
                List = AllList.Where(A => A.FatherTreeId == ParentClassifyId).OrderBy(A => A.NodeName).ToList();
                //
            }
            else
            {
                List = AllList.Where(A => string.IsNullOrEmpty(A.FatherTreeId)).ToList();

            }
            if (List != null)
            {
                foreach (var item in List)
                {
                    item.children = BuildTreeModel(AllList,item.TreeId);
                    if (item.children.Count == 0)
                    {
                        item.children = null;
                    }
                }

            }
            return List.ToList();
        }

通過上述代碼，我們構造了如下數據，工程類（擁有8個子類）->工程類子類中的安裝類（擁有11個子類）->......等等，多層次關系！

截止到這兒，樹的構造就完成了！

二、如何查詢：

 如果直接查詢數據表，SQL支持的遞歸查詢我們可以用With....As..關鍵字來進行查詢，具體查詢語法請參考我的博客：SqlServer共用表達式（CTE）With As 處理遞歸查詢

在此，僅做簡單范例，如下：

1、查詢子分類，要求帶出該子分類的所有上級元素

WITH CTE_Tree(TreeId,NodeName,FatherTreeId )
 AS 
 (SELECT TreeId,NodeName,FatherTreeId
 FROM dbo.TreeTable 
 WHERE NodeName = '電梯工程' 
 UNION ALL 
 SELECT o.TreeId,o.NodeName,o.FatherTreeId
 FROM dbo.TreeTable o INNER JOIN CTE_Tree oo ON o.TreeId=oo.FatherTreeId) 
 SELECT distinct * FROM CTE_Tree

查詢結果如下：

說明：查詢NodeName為電梯工程的分類，帶出了電梯工程的所有上級關系！

2、查詢上級元素，要求帶出所有下級元素

WITH CTE_Tree(TreeId,NodeName,FatherTreeId )
 AS 
 (SELECT TreeId,NodeName,FatherTreeId
 FROM dbo.TreeTable 
 WHERE NodeName = '安裝類' 
 UNION ALL 
 SELECT o.TreeId,o.NodeName,o.FatherTreeId
 FROM dbo.TreeTable o INNER JOIN CTE_Tree oo ON o.FatherTreeId=oo.TreeId) 
 SELECT distinct * FROM CTE_Tree order by NodeName

查詢結果如下：

安裝類及11個子類全部查詢出來！

如果我們不使用SQL的... with.... as.....語句，要查詢出父節點及該節點下的所有子節點，該怎么查詢呢？

通過遞歸List<T>查詢方法如下：

 /// <summary>
        /// 根據父節點ID 查詢該節點及該節點下的所有子節點
        /// </summary>
        /// <param name="FatherNodeId"></param>
        /// <returns></returns>
        public static List<TreeTableModel> QueryTreeByFatherId(string FatherNodeId)
        {
            using (AnFuDBEntities context = new AnFuDBEntities())
            {
                List<TreeModel> TreeList = new List<TreeModel>();
                var data = context.TreeTable.ToList();
                var list = new List<TreeTableModel>();
                list = Mapper.DynamicMap<List<TreeTableModel>>(data);
                List<TreeTableModel> treeNodes = new List<TreeTableModel>();
                //安裝類 對應的Id ： 650FEF5E-21E6-404A-B8F7-12E82548D432
                new QueryTreeModel().GetTreeNodes(list, FatherNodeId, ref treeNodes);
                var ef = list.Where(A => A.TreeId == FatherNodeId).FirstOrDefault();
                treeNodes.Add(ef);//為了和數據庫 as with 遞歸查詢一致，將此節點加入返回值中
                return treeNodes;
            }
        }


 /// <summary>
        /// 根據父類節點，查詢出所有子節點
        /// </summary>
        /// <param name="list">數據源，非樹狀結構</param>
        /// <param name="TreeId">父節點Id</param>
        /// <param name="treeNodes">得到的子節點</param>
        public  void GetTreeNodes(List<TreeTableModel> list, string TreeId, ref List<TreeTableModel> treeNodes)
        {
            if (list == null)
                return;
            List<TreeTableModel> sublist;
            if (!string.IsNullOrWhiteSpace(TreeId))
            {
                sublist = list.Where(t => t.FatherTreeId == TreeId).ToList();
            }
            else
            {
                sublist = list.Where(t => string.IsNullOrWhiteSpace(t.FatherTreeId)).ToList();
            }
            if (!sublist.Any())
                return;
            foreach (var item in sublist)
            {
                treeNodes.Add(new TreeTableModel() { TreeId=item.TreeId, FatherTreeId=item.FatherTreeId, NodeName=item.NodeName});
                GetTreeNodes(list, item.TreeId, ref treeNodes);
            }
        }

執行上述待代碼：

 //安裝類 對應的Id ： 650FEF5E-21E6-404A-B8F7-12E82548D432
 AnfuUser.QueryTreeByFatherId("650FEF5E-21E6-404A-B8F7-12E82548D432");

結果如下：

根據截圖可知，我們查詢到12條記錄！

那么，我們執行SQL如下，看看結果是否一致，如下：

 根據上下兩個截圖，我們得知，查詢結果一致！

那么，如果我們要根據子節點，查詢該節點及所有上級節點，怎么通過程序查詢呢？

代碼如下：

  /// <summary>
        /// 根據子ID 獲取自身節點及所有父節點
        /// </summary>
        /// <param name="FatherNodeId"></param>
        /// <returns></returns>
        public static List<TreeTableModel> QueryTreeByChildId(string FatherNodeId)
        {
            using (AnFuDBEntities context = new AnFuDBEntities())
            {
                List<TreeModel> TreeList = new List<TreeModel>();
                var data = context.TreeTable.ToList();
                var list = new List<TreeTableModel>();
                list = Mapper.DynamicMap<List<TreeTableModel>>(data);
                List<TreeTableModel> treeNodes = new List<TreeTableModel>();
                //安裝類 對應的Id ： 650FEF5E-21E6-404A-B8F7-12E82548D432
                new QueryTreeModel().GetTreeNodesByChildId(list, FatherNodeId, ref treeNodes);
                var ef = list.Where(A => A.TreeId == FatherNodeId).FirstOrDefault();
                treeNodes.Add(ef);//為了和數據庫 as with 遞歸查詢一致，將此節點加入返回值中
                return treeNodes;
            }
        }


   /// <summary>
        /// 根據子節點，查詢出所有父節點
        /// </summary>
        /// <param name="list">數據源，非樹狀結構</param>
        /// <param name="TreeId">子節點Id</param>
        /// <param name="treeNodes">得到的子節點</param>
        public void GetTreeNodesByChildId(List<TreeTableModel> list, string TreeId, ref List<TreeTableModel> treeNodes)
        {
            if (list == null)
                return;
            var ef = list.Where(A => A.TreeId == TreeId).FirstOrDefault();
            if (ef == null)
                return;
            List<TreeTableModel> sublist;
            if (!string.IsNullOrWhiteSpace(TreeId))
            {
                var FatherTreeId = ef.FatherTreeId;
                sublist = list.Where(t => t.TreeId == FatherTreeId).ToList();
            }
            else
            {
                sublist = list.Where(t => !string.IsNullOrWhiteSpace(t.FatherTreeId)).ToList();
            }
            if (!sublist.Any())
                return;
            foreach (var item in sublist)
            {
                treeNodes.Add(new TreeTableModel() { TreeId = item.TreeId, FatherTreeId = item.FatherTreeId, NodeName = item.NodeName });
                GetTreeNodesByChildId(list, item.TreeId, ref treeNodes);
            }
        }

執行上述代碼，我們查詢電梯工程及它的所有上級節點，

AnfuUser.QueryTreeByChildId("75269B3A-0086-40A9-BE18-62820E662B69");

結果如下：

我們再通過SQL查詢如下：

WITH CTE_Tree(TreeId,NodeName,FatherTreeId )
 AS 
 (SELECT TreeId,NodeName,FatherTreeId
 FROM dbo.TreeTable 
 WHERE TreeId = '75269B3A-0086-40A9-BE18-62820E662B69' 
 UNION ALL 
 SELECT o.TreeId,o.NodeName,o.FatherTreeId
 FROM dbo.TreeTable o INNER JOIN CTE_Tree oo ON o.TreeId=oo.FatherTreeId) 
 SELECT distinct * FROM CTE_Tree

結果如下：

比對二者查詢結果是否一致呢？

 @陳卧龍的博客