C# 递归构造树状数据结构（泛型），如何构造？如何查询？

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首先，我们需要准备一张表，如下范例：

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

为了节约时间，我直接沿用项目中的数据，作如下批量插入：

insert into TreeTable(TreeId,NodeName,FatherTreeId)
select [SpClassifyId],[ClassifyName],[ParentClassifyId]
from [dbo].[SM_SupplierClassify]
where [ForefatherClassifyName] in('工程类','精装修类','设计类','营销类')

插入的数据，如下所示：

从上图，我们可以看出，这些数据中有四种大类，分别为：('工程类','精装修类','设计类','营销类')，层级关系通过FatherTreeId构造，当然，此表中的层次不仅仅只有两级，理论上支持N级，类似这种结构的数据现实生活中有很多，如：家谱，人员组织架构，营销模式（微信的吸粉，病毒式营销），甚至传销模式等等

那么，我们如何将上述数据转变为树状结构的数据类型呢？

大家都会想到递归，但如何递归呢？

两种方法，

一、如何构造：

1、递归式查询，从根节点入手，查询多次（效率非常低，在此不作介绍）

2、一次性查询出所有数据，根据FatherTreeId，递归式查询泛型（效率高。只查询一次即可）我们介绍此种方法：

首先，我们构造如下Model

    /// <summary>
    /// 我们要构造的树
    /// </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>
    /// 数据库表对应的实体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; }
        //子数据
        public List<TreeTableModel> children { get; set; }
    }

上述的TreeModel中的 MakeTree 方法用于递归构造树！~_~ 重点

构造方法如下：

        /// <summary>
        /// 构造树
        /// </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>
        /// 递归方法，构造树状泛型
        /// </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 == )
                    {
                        item.children = null;
                    }
                }

            }
            return List.ToList();
        }

通过上述代码，我们构造了如下数据，工程类（拥有8个子类）->工程类子类中的安装类（拥有11个子类）->......等等，多层次关系！

截止到这儿，树的构造就完成了！

二、如何查询：

如果直接查询数据表，SQL支持的递归查询我们可以用With....As..关键字来进行查询，具体查询语法请参考我的博客：SqlServer共用表达式（CTE）With As 处理递归查询

在此，仅做简单范例，如下：

1、查询子分类，要求带出该子分类的所有上级元素

WITH CTE_Tree(TreeId,NodeName,FatherTreeId )
 AS
 (SELECT TreeId,NodeName,FatherTreeId
 FROM dbo.TreeTable
 WHERE NodeName = '电梯工程'
 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

查询结果如下：

说明：查询NodeName为电梯工程的分类，带出了电梯工程的所有上级关系！

2、查询上级元素，要求带出所有下级元素

WITH CTE_Tree(TreeId,NodeName,FatherTreeId )
 AS
 (SELECT TreeId,NodeName,FatherTreeId
 FROM dbo.TreeTable
 WHERE NodeName = '安装类'
 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

查询结果如下：

安装类及11个子类全部查询出来！

如果我们不使用SQL的... with.... as.....语句，要查询出父节点及该节点下的所有子节点，该怎么查询呢？

通过递归List<T>查询方法如下：

 /// <summary>
        /// 根据父节点ID 查询该节点及该节点下的所有子节点
        /// </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>();
                //安装类 对应的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);//为了和数据库 as with 递归查询一致，将此节点加入返回值中
                return treeNodes;
            }
        }

 /// <summary>
        /// 根据父类节点，查询出所有子节点
        /// </summary>
        /// <param name="list">数据源，非树状结构</param>
        /// <param name="TreeId">父节点Id</param>
        /// <param name="treeNodes">得到的子节点</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);
            }
        }

执行上述待代码：

 //安装类 对应的Id ： 650FEF5E-21E6-404A-B8F7-12E82548D432
 AnfuUser.QueryTreeByFatherId("650FEF5E-21E6-404A-B8F7-12E82548D432");

结果如下：

根据截图可知，我们查询到12条记录！

那么，我们执行SQL如下，看看结果是否一致，如下：

根据上下两个截图，我们得知，查询结果一致！

那么，如果我们要根据子节点，查询该节点及所有上级节点，怎么通过程序查询呢？

代码如下：

  /// <summary>
        /// 根据子ID 获取自身节点及所有父节点
        /// </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>();
                //安装类 对应的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);//为了和数据库 as with 递归查询一致，将此节点加入返回值中
                return treeNodes;
            }
        }

   /// <summary>
        /// 根据子节点，查询出所有父节点
        /// </summary>
        /// <param name="list">数据源，非树状结构</param>
        /// <param name="TreeId">子节点Id</param>
        /// <param name="treeNodes">得到的子节点</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);
            }
        }

执行上述代码，我们查询电梯工程及它的所有上级节点，

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

结果如下：

我们再通过SQL查询如下：

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

结果如下：

比对二者查询结果是否一致呢？

@陈卧龙的博客