使用 linq 按父项对对象列表进行分组以输出子元素

Question

I have a silly problem with a linq groupby I just cant get to work on my own.

Basically I have a list of items that I am trying to group together by its parentId outing the details

var list = new List<GroupItem>()
{
    new GroupItem() {Id = 1, Name = ".net"},
    new GroupItem() {Id = 2, Name = "asp.net", ParentId = 1},
    new GroupItem(){Id = 3,Name = "c#",ParentId = 1},
    new GroupItem(){Id = 4,Name = "php"},
    new GroupItem(){Id = 5,Name = "zend",ParentId = 4}
};

var group = from g in list
            group g by g.ParentId ==null
                into grouped
            select new
            {
                FrameworkId = grouped.Key,
                Items = (from g in list
                        where g.ParentId==g.ParentId
                        select g).ToList()

            };

foreach (var gi in group)
{

    Console.WriteLine(gi.FrameworkId);
    foreach (var item in gi.Items)
    {
        Console.WriteLine(item.Name);
    }
}

What am I doing wrong?

Answer 1

You query seems to be too complicated:

1. You should group by ParentId for items that have it not null
2. You do not need to find the items again by matching ParentId because GroupBy operator does it for you

My preferred solution:

list.Where(x => x.ParentId != null)
    .GroupBy(x => x.ParentId, 
             (key, elements) => 
                new {
                  FrameworkId = key,
                  Items = elements.ToList()
                })
    .ToList();

Answer 2

You can Directlly use this query for filtering Data.

if you want the data which don't have ParentID then you can use below mentioned query

 var gr = list.Where(p => p.ParentId == 0).ToList();

and if you want the data who have the Parent Id then you can use below mentioned code

 var gr1 = list.Where(p => p.ParentId != 0).ToList();

Answer 3

here is my solution:

 list.Where(x => x.ParentId != null)
  .GroupBy(x => x.ParentId)
  .Select(x => new ParentViewModel {
     ParentId = x.Key.ParentId,
     Parent = x.ToList()
  })
  .ToList();

Now you will get child items in Parent object of ParentViewModel , eg Parent.Items