递归 LINQ 查询:选择项目和所有带有子子项的子项 [英] Recursive LINQ query: select item and all children with subchildren
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问题描述
有什么方法可以编写一个 LINQ(或程序风格)查询,它可以选择一个项目和一个查询的所有子项?我有实体:
Is there any way to write a LINQ (or procedural style) query, that can select an item and all children with one query? I have entity:
public class Comment
{
public int Id {get;set;}
public int ParentId {get;set;}
public int Text {get;set;}
}
我有一个 ID,所以我想选择带有 ID 的评论及其所有带有子子项的子项.示例:
I have an ID, so I want to select Comment with ID and all its children with subchildren. Example:
1
-2
--3
-4
-5
--6
2
3
如果 ID == 1 那么我想要 1,2,3,4,5,6 的列表.
If ID == 1 then I want list of 1,2,3,4,5,6.
推荐答案
public class Comment
{
public int Id { get; set; }
public int ParentId { get; set; }
public string Text { get; set; }
public List<Comment> Children { get; set; }
}
class Program
{
static void Main()
{
List<Comment> categories = new List<Comment>()
{
new Comment () { Id = 1, Text = "Item 1", ParentId = 0},
new Comment() { Id = 2, Text = "Item 2", ParentId = 0 },
new Comment() { Id = 3, Text = "Item 3", ParentId = 0 },
new Comment() { Id = 4, Text = "Item 1.1", ParentId = 1 },
new Comment() { Id = 5, Text = "Item 3.1", ParentId = 3 },
new Comment() { Id = 6, Text = "Item 1.1.1", ParentId = 4 },
new Comment() { Id = 7, Text = "Item 2.1", ParentId = 2 }
};
List<Comment> hierarchy = new List<Comment>();
hierarchy = categories
.Where(c => c.ParentId == 0)
.Select(c => new Comment() {
Id = c.Id,
Text = c.Text,
ParentId = c.ParentId,
Children = GetChildren(categories, c.Id) })
.ToList();
HieararchyWalk(hierarchy);
Console.ReadLine();
}
public static List<Comment> GetChildren(List<Comment> comments, int parentId)
{
return comments
.Where(c => c.ParentId == parentId)
.Select(c => new Comment {
Id = c.Id,
Text = c.Text,
ParentId = c.ParentId,
Children = GetChildren(comments, c.Id) })
.ToList();
}
public static void HieararchyWalk(List<Comment> hierarchy)
{
if (hierarchy != null)
{
foreach (var item in hierarchy)
{
Console.WriteLine(string.Format("{0} {1}", item.Id, item.Text));
HieararchyWalk(item.Children);
}
}
}
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