递归林格集团 [英] Recursive Linq Grouping

问题描述

方案：
我有数据库表存储另一个表的多对多关系的层次结构。一个项目可以有多个孩子，也可以有多个父母。

Scenario: I have database table that stores the hierarchy of another table's many-to-many relationship. An item can have multiple children and can also have more than one parent.

Items    
------ 
ItemID (key)

Hierarchy
---------
MemberID (key)
ParentItemID (fk)
ChildItemID (fk)

样本层次结构：

Level1  Level2  Level3
X       A       A1
                A2
        B       B1
                X1
Y       C

我想将所有小孩节点分组，每个 / strong>节点。

I would like to group all of the child nodes by each parent node in the hierarchy.

Parent  Child
X       A1
        A2
        B1
        X1
A       A1
        A2
B       B1
        X1
Y       C

注意在Parent列中没有叶节点，以及Child列如何仅包含叶子节点。 >

理想情况下，我想要t他的结果是以 IEnumerable <\\ c $ c> IGrouping 项目，项目>> 的形式，其中的关键是父母，组的项目都是儿童

理想情况下，我想要一个实体提供商可以转换为T-SQL的解决方案，但是如果不可能，那么我需要保持最小的往返行程。

我打算将存在于另一个表中的值加在叶节点上。

• Notice how there are no leaf nodes in the Parent column, and how the Child column only contains leaf nodes.
• Ideally, I would like the results to be in the form of IEnumerable<IGrouping<Item, Item>> where the key is a Parent and the group items are all Children.
• Ideally, I would like a solution that the entity provider can translate in to T-SQL, but if that is not possible then I need to keep round trips to a minimum.
• I intend to Sum values that exist in another table joined on the leaf nodes.

推荐答案

由于你总是返回表中的所有项目，为什么不做一个递归方法来获取父项的所有子代，然后在内存中的项目中使用：

Since you are always going to be returning ALL of the items in the table, why not just make a recursive method that gets all children for a parent and then use that on the in-memory Items:

partial class Items
{
    public IEnumerable<Item> GetAllChildren()
    {
        //recursively or otherwise get all the children (using the Hierarchy navigation property?)
    }
}

然后：

var items = 
    from item in Items.ToList()
    group new 
    {
        item.itemID,
        item.GetAllChildren()
    } by item.itemID;

对不起，任何语法错误...

Sorry for any syntax errors...

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