Linq中的分层数据-选项和性能

这 option 也可能证明有用:

LINQ AsHierarchy()扩展方法
http://www.scip.be/index.php?Page=ArticlesNET18

它不仅允许单亲关系,还允许多亲关系、级别指示和不同类型的关系:

CREATE TABLE Person (
  Id INTEGER,
  Name TEXT
);

CREATE TABLE PersonInPerson (
  PersonId INTEGER NOT NULL,
  InPersonId INTEGER NOT NULL,
  Level INTEGER,
  RelationKind VARCHAR(1)
);

CREATE TABLE [dbo].[hierarchical_table](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [parent_id] [int] NULL,
    [data] [varchar](255) NOT NULL,
 CONSTRAINT [PK_hierarchical_table] PRIMARY KEY CLUSTERED 
(
    [id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

CREATE VIEW [dbo].[vw_recursive_view]
AS
WITH hierarchy_cte(id, parent_id, data, lvl) AS
(SELECT     id, parent_id, data, 0 AS lvl
      FROM         dbo.hierarchical_table
      WHERE     (parent_id IS NULL)
      UNION ALL
      SELECT     t1.id, t1.parent_id, t1.data, h.lvl + 1 AS lvl
      FROM         dbo.hierarchical_table AS t1 INNER JOIN
                            hierarchy_cte AS h ON t1.parent_id = h.id)
SELECT     id, parent_id, data, lvl
FROM         hierarchy_cte AS result


CREATE FUNCTION [dbo].[fn_tree_for_parent] 
(
    @parent int
)
RETURNS 
@result TABLE 
(
    id int not null,
    parent_id int,
    data varchar(255) not null,
    lvl int not null
)
AS
BEGIN
    WITH hierarchy_cte(id, parent_id, data, lvl) AS
   (SELECT     id, parent_id, data, 0 AS lvl
        FROM         dbo.hierarchical_table
        WHERE     (id = @parent OR (parent_id IS NULL AND @parent IS NULL))
        UNION ALL
        SELECT     t1.id, t1.parent_id, t1.data, h.lvl + 1 AS lvl
        FROM         dbo.hierarchical_table AS t1 INNER JOIN
            hierarchy_cte AS h ON t1.parent_id = h.id)
    INSERT INTO @result
    SELECT     id, parent_id, data, lvl
    FROM         hierarchy_cte AS result
RETURN 
END

ALTER TABLE [dbo].[hierarchical_table]  WITH CHECK ADD  CONSTRAINT [FK_hierarchical_table_hierarchical_table] FOREIGN KEY([parent_id])
REFERENCES [dbo].[hierarchical_table] ([id])

ALTER TABLE [dbo].[hierarchical_table] CHECK CONSTRAINT [FK_hierarchical_table_hierarchical_table]

要使用它,您可以执行以下操作--假设某种合理的命名方案:

using (DataContext dc = new HierarchicalDataContext())
{
    HierarchicalTableEntity h = (from e in dc.HierarchicalTableEntities
                                 select e).First();
    var query = dc.FnTreeForParent( h.ID );
    foreach (HierarchicalTableViewEntity entity in query) {
        ...process the tree node...
    }
}

1. 根据用户输入驱动对树的每一层的检索。设想一个树视图控件填充了根节点、根的子节点和根的孙子节点。只有根和子对象被展开(子对象被折叠隐藏)。当用户展开子节点时,将显示根节点的孙子节点(以前已检索并隐藏),并启动对所有曾孙节点的检索。对N层深重复该模式。此模式对于大型树(深度或宽度)非常有效,因为它只检索所需的树部分。
2. great article

public static IEnumerable<T> ByHierarchy<T>(
 this IEnumerable<T> source, Func<T, bool> startWith, Func<T, T, bool> connectBy)
{
  if (source == null)
   throw new ArgumentNullException("source");

  if (startWith == null)
   throw new ArgumentNullException("startWith");

  if (connectBy == null)
   throw new ArgumentNullException("connectBy");

  foreach (T root in source.Where(startWith))
  {
   yield return root;
   foreach (T child in source.ByHierarchy(c => connectBy(root, c), connectBy))
   {
    yield return child;
   }
 }
}

我是这样称呼它的:

comments.ByHierarchy(comment => comment.ParentNum == parentNum, 
 (parent, child) => child.ParentNum == parent.CommentNum && includeChildren)

here .

在MS SQL 2008中,您可以使用 HierarchyID 直接来说,在sql2005中,您可能需要手动实现它们。ParentID在大型数据集上没有那么好的性能。也检查 this article 有关该主题的更多讨论。

这个方法是我从 Rob Conery's blog (查看第6部分的代码,也可以查看codeplex)我喜欢使用它。可以对其进行重构以支持多个“子”级别。

var categories = from c in db.Categories
                 select new Category
                 {
                     CategoryID = c.CategoryID,
                     ParentCategoryID = c.ParentCategoryID,
                     SubCategories = new List<Category>(
                                      from sc in db.Categories
                                      where sc.ParentCategoryID == c.CategoryID
                                      select new Category {
                                        CategoryID = sc.CategoryID, 
                                        ParentProductID = sc.ParentProductID
                                        }
                                      )
                             };

从客户端获取数据的问题在于,您永远无法确定需要深入到多深。此方法将对每个深度执行一次往返,并且可以在一次往返中从0执行到指定深度。

public IQueryable<Node> GetChildrenAtDepth(int NodeID, int depth)
{
  IQueryable<Node> query = db.Nodes.Where(n => n.NodeID == NodeID);
  for(int i = 0; i < depth; i++)
    query = query.SelectMany(n => n.Children);
       //use this if the Children association has not been defined
    //query = query.SelectMany(n => db.Nodes.Where(c => c.ParentID == n.NodeID));
  return query;
}

http://support.microsoft.com/default.aspx?scid=kb;en-us;q248915