如何使用linq爲類別和子類別創建麪包屑導航

Question

如何爲其父類使用其列名指定的無限子類別創建麪包類別？

設想以下表項：

id name  parentid 
========================= 
1  animal NULL 
2  veg  NULL 
3  mineral NULL 
4  doggie 1 
5  kittie 1 
6  horsie 1 
7  gerbil 1 
8  birdie 1 
9  carrot 2 
10 tomato 2 
11 potato 2 
12 celery 2 

Answer 1

如果遞歸函數的全套工作是確定的，則以下應該工作。我把它一起扔在LINQPad。神奇的是遞歸函數GetBreadcrumbs。我在小狗下添加了第三級「拳擊手」。

void Main() 
{ 
    var list = new List<MyEntity>() 
    { 
     new MyEntity() { Id = 1, Name = "animal" }, 
     new MyEntity() { Id = 2, Name = "veg" }, 
     new MyEntity() { Id = 3, Name = "mineral" }, 
     new MyEntity() { Id = 4, Name = "doggie", ParentId = 1 }, 
     new MyEntity() { Id = 5, Name = "kittie", ParentId = 1 }, 
     new MyEntity() { Id = 6, Name = "horsie", ParentId = 1 }, 
     new MyEntity() { Id = 7, Name = "gerbil", ParentId = 1 }, 
     new MyEntity() { Id = 8, Name = "birdie", ParentId = 1 }, 
     new MyEntity() { Id = 9, Name = "carrot", ParentId = 2 }, 
     new MyEntity() { Id = 10, Name = "tomato", ParentId = 2 }, 
     new MyEntity() { Id = 11, Name = "potato", ParentId = 2 }, 
     new MyEntity() { Id = 12, Name = "celery", ParentId = 2 }, 
     new MyEntity() { Id = 13, Name = "boxer", ParentId = 4 }, 
    }; 

    var breadcrumbs = GetBreadcrumbs(list); 
    foreach (var breadcrumb in breadcrumbs) 
     Console.WriteLine(breadcrumb); 

} 

// This is where the Magic happens! 
public IEnumerable<string> GetBreadcrumbs(IEnumerable<MyEntity> entities, int? parentId = null) 
{ 
    var parents = entities.Where(x => x.ParentId == parentId); 
    var children = entities.Where(x => x.ParentId != parentId); 

    foreach (var parent in parents) 
    { 
     yield return parent.Name; 
     foreach (var trail in GetBreadcrumbs(children, parent.Id)) 
      yield return (parent.Name + " > " + trail); 
    } 
} 

public class MyEntity 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
    public int? ParentId { get; set; } 
}