LINQ to SQL - Grouping categories by parentId - asp.net-mvc

Question

I am trying to construct a navigation menu using a Categories table from my db.
I have a similar layout as below in Categories table.
public List<Category> CategoryData = new List(new Category[] {
new Category{ CategoryId = 1, Name = "Fruit", ParentCategoryId = null},
new Category{ CategoryId = 2, Name = "Vegetables", ParentCategoryId = null},
new Category{ CategoryId = 3, Name = "Apples", ParentCategoryId = 1},
new Category{ CategoryId = 4, Name = "Bananas", ParentCategoryId = 1},
new Category{ CategoryId = 5, Name = "Cucumber", ParentCategoryId = 2},
new Category{ CategoryId = 6, Name = "Onions", ParentCategoryId = 2}
); }
The above should return something like
Fruit (parent)
"===Apples, Bananas (child)
Vegetables (parent)
"===Cucumber, Onions (child)
I need to be able to pass this as some kind of 'grouped' (grouped by parentid) collection to my View.
How to do this?

Answer 1

It would seem like this is a good example of when translating your model to a viewModel would come in handy. As you could create a collection of CategoryViewModel which have a Childrens property of CategoryViewModel using the same technique describe by #thomas.
public class CategoryViewModel
{
public int CategoryId { set; get; }
public string CategoryName { set; get; }
public int? ParentCategoryId { set; get; }
public IEnumerable<CategoryViewModel> Children { set; set; }
}
public static IEnumerable<CategoryViewModel> GetAllCategoryViewModel(IList<Category> categories)
{
var query = GetChildren(null, categories);
return query.ToList();
}
public static IEnumerable<CategoryViewModel> GetChildren(int? parentId, IList<Category> categories)
{
var children = from category in categories
where category.ParentCategoryId == parentId
select
new CategoryViewModel
{
CategoryId = category.CategoryId,
CategoryName = category.CategoryName,
ParentCategoryId = category.ParentCategoryId,
Children = GetChildren(category.CategoryId, categories)
};
return children;
}

Answer 2

How about something like:
private void Test()
{
var categoryData = new List
{
new Category {CategoryId = 1, Name = "Fruit", ParentCategoryId = null},
new Category {CategoryId = 2, Name = "Vegetables", ParentCategoryId = null},
new Category {CategoryId = 3, Name = "Apples", ParentCategoryId = 1},
new Category {CategoryId = 4, Name = "Bananas", ParentCategoryId = 1},
new Category {CategoryId = 5, Name = "Cucumber", ParentCategoryId = 2},
new Category {CategoryId = 6, Name = "Onions", ParentCategoryId = 2}
};
var query = from category in categoryData
where category.ParentCategoryId == null
select category;
foreach ( var item in query )
{
Debug.WriteLine( string.Format( "{0} (parent)", item.Name ) );
Debug.WriteLine( GetChildren(item.CategoryId, categoryData ) );
}
}
private static string GetChildren( int parentCategoryId, IEnumerable categoryData)
{
var children = ( from category in categoryData
where category.ParentCategoryId == parentCategoryId
select category.Name ).ToArray();
return string.Format( "==={0} (child)", string.Join( ", ", children ) );
}

Answer 3

var list = from a in CategoryData
join b in CategoryData on a.ParentCategoryId equals b.CategoryId into c
from d in c.DefaultIfEmpty()
where d != null
select new {
a.CategoryId,
a.Name,
a.ParentCategoryId,
ParentName = d.Name
};
returns
CategoryId Name ParentCategoryId ParentName
3 Apples 1 Fruit
4 Bananas 1 Fruit
5 Cucumber 2 Vegetables
6 Onions 2 Vegetables
You can then loop through it in your view and format accordingly.