将 sql 层次结构读入 c# 对象

Question

您将如何读取 SQL 数据以获取单位的分层列表？

不依赖于仅 SQL Server 的解决方案？

public class Unit {
    public Unit Parent { get; set; }
    public int Id { get; set; }
    public String Name { get; set; }
}

List<Unit> list = new List<Unit>();

while(reader.Read())
{
    // read sql data into clr object UNIT
}

表格有 3 列：

Id| ParentId | Name
1 | Null     | bla
2 |   1      | x
3 |   1      | y
4 |   2      | z
5 |   2      | test

更新：

That is the code which is taken from user marc_s:

 List<Unit> units = new List<Unit>();

            String commandText =
            @";WITH Hierarchy AS
              (
                 SELECT
                    ID,  ParentID = CAST(NULL AS INT),
                    Name, HierLevel = 1
                 FROM
                    dbo.Unit
                 WHERE
                    ParentID IS NULL

                 UNION ALL

                 SELECT
                    ht.ID, ht.ParentID, ht.Name, h1.HierLevel + 1
                 FROM
                    dbo.Unit ht
                 INNER JOIN 
                    Hierarchy h1 ON ht.ParentID = h1.ID
              )
              SELECT Id, ParentId, Name
              FROM Hierarchy
              ORDER BY HierLevel, Id";

            using(SqlConnection con = new SqlConnection(_connectionString))
            using (SqlCommand cmd = new SqlCommand(commandText, con))
            {
                con.Open();

                // use SqlDataReader to iterate over results
                using (SqlDataReader rdr = cmd.ExecuteReader())
                {
                    while (rdr.Read())
                    {
                        // get the info from the reader into the "Unit" object
                        Unit thisUnit = new Unit();

                        thisUnit.Id = Convert.ToInt32(rdr["Id"]);
                        thisUnit.UnitName = rdr["Name"].ToString();                     

                        // check if we have a parent
                        if (rdr["ParentId"] != DBNull.Value)
                        {
                            // get ParentId
                            int parentId = Convert.ToInt32(rdr["ParentId"]);

                            // find parent in list of units already loaded
                            // NOTE => not needed anymore => Unit parent = units.FirstOrDefault(u => u.Id == parentId);

                            // Instead use this method to find the parent:


                            Unit parent = FindParentUnit(units, parentId);

                            // if parent found - set this unit's parent to that object
                            if (parent != null)
                            {
                                thisUnit.Parent = parent;
                                parent.Children.Add(thisUnit);
                            }
                        }
                       else
                       {
                           units.Add(thisUnit);
                       }
                    }
                }
            }

            return units;

这是填充列表的屏幕截图

http://oi41.tinypic.com/rmpe8n.jpg

这是 Unit 表中的 sql 数据：

http://oi40.tinypic.com/mt12sh.jpg

问题：

实际上填充的列表应该只有一个单元对象而不是 11（索引 0 - 10）。是的，列表中的第一个单元已正确填充，但索引 1 - 10 的单元不应出现在列表中。

实际上应该是这样的：

0
|--1
|   |--3
|   |   |--9
|   |   |--10  
|   |--4
|--2
|   |--5
|   |--6
|--7
|--8

更新和解决方案

private static Unit FindParentUnit(List<Unit> units, int parentId)
        {
            Unit parent;
            foreach (Unit u in units)
            {
                if (u.Id == parentId){
                    return u;                                    
                }
                parent = FindParentUnit(u.Children, parentId);
                if (parent != null)
                    return parent;
            }
            return null;
        } 

Answer 1

一种方法是使用对象关系映射器，例如实体框架来为您完成工作。 This answer 类似的 EF 问题应该会为您指明正确的方向。

Answer 2

应该这样做:-)

// set up connection string
string connectionString = "server=.;database=test;integrated Security=SSPI;";

// define a CTE (Common Table Expression) to recursively build your hierarchical
// structure into a flat list and order it according to its "sequence" (root first)
string cteStatement =
            @";WITH Hierarchy AS
              (
                 SELECT
                    ID,  ParentID = CAST(NULL AS INT),
                    Name, HierLevel = 1
                 FROM
                    dbo.HierarchyTest   -- replace with your table name!
                 WHERE
                    ParentID IS NULL

                 UNION ALL

                 SELECT
                    ht.ID, ht.ParentID, ht.Name, h1.HierLevel + 1
                 FROM
                    dbo.HierarchyTest ht   -- replace with your table name!
                 INNER JOIN 
                    Hierarchy h1 ON ht.ParentID = h1.ID
              )
              SELECT Id, ParentId, Name
              FROM Hierarchy
              ORDER BY HierLevel, Id";

// set up list of "Unit" objects
List<Unit> units = new List<Unit>();

// create connection and command to query             
using(SqlConnection conn = new SqlConnection(connectionString))
using(SqlCommand cmd = new SqlCommand(cteStatement, conn))
{
    conn.Open();

    // use SqlDataReader to iterate over results
    using(SqlDataReader rdr = cmd.ExecuteReader())
    {
        while(rdr.Read())
        {
            // get the info from the reader into the "Unit" object
            Unit thisUnit = new Unit();

            thisUnit.Id = rdr.GetInt32(0);
            thisUnit.Name = rdr.GetString(2);
            thisUnit.Children = new List<Unit>();

            // check if we have a parent
            if(!rdr.IsDBNull(1))
            {
                // get ParentId
                int parentId = rdr.GetInt32(1);

                // find parent in list of units already loaded
                Unit parent = units.FirstOrDefault(u => u.Id == parentId);

                // if parent found - set this unit's parent to that object
                if(parent != null)
                {
                    thisUnit.Parent = parent;
                    parent.Children.Add(thisUnit);
                }
            }
            else
            {
                units.Add(thisUnit);
            }
        }
    }

    conn.Close();
}

这对你有用吗？

CTE（通用表表达式）递归地扫描您的表并建立分层节点列表 - 通过按“层次结构级别”对其进行排序，您可以确保在其子节点出现之前获取所有父节点（以便代码工作）

更新： 好的，看来您想将 only 节点与 no parent 放入结果列表中 - 这很好（但您没有'不是真的说你想要那样!!） - 我更新了上面的代码 - 请重新检查！

Answer 3

您的数据代表一个树结构，您只需要构建树创建根单元并添加叶子。您可以使用字典而不是列表在树中搜索，这很简单。 这是一个仅在行按 id 升序排序时才有效的示例：

Dictionary<Int32,Unit> dic = new Dictionary<Int32,Unit>();

while(reader.Read()) 
{ 
    //create the new Unit
    // if the parent is not null get the parent unit from dic
    // add the new Unit to dic
}