LINQ Query to Produce Non-Empty Nested Menu?

Question

To see my problem in action, visit www.apoads.com and hover over the "Local Businesses" menu item. It's a series of nested unordered lists generated from a db call. Go ahead and click on a few of the items underneath "Local Businesses", you'll see that most of the categories are empty (the site is very new).

Problem: I only want to show the categories that actually contain a local business. Here's what my category schema looks like:

int BizCatID - PK,Identity (used in FK relation to the table named Biz)
int? ParentID - BizCatID of this rows parentID, null means no parent
nvarchar Name - name of the category
nvarchar Caption - quick description of the category

What I've tried: I've tried to update my LINQ query like so:

from c in db.BizCategories where c.ParentID != null && c.Bizs.Count() > 0 select c;

That obviously won't work, cause I'll need the parent category to show if the child category contains a business. So I tried this:

from c in db.BizCategories where c.Bizs.Count() > 0 select c;

This doesn't work either, as parent categories will never have any businesses under them. So it seems like I'll need to do some sort of inverse recursion, but I'm not sure how to do that.

Or, perhaps I'm making things to hard for myself and I need to change my db schemas?

Answer 1

I'm not sure about the recursion bit but this might get you started. Is a two-level query. I'm guessing you want to support any number of levels.

var allcats = (from c in db. BizCategories
               select c).ToList(); // This will retrieve them all from the database.

var twoLevels = from c in allcats
                where c.ParentID == null
                select new {
                             Name = c.Name, Caption = c.Caption,
                             Children = 
                             from d in allcats 
                             where d.ParentID == c.BizCatID
                             select d
                           };

Answer 2

A query like this is getting close to what I need:

from c in BizCategories
    where c.ParentID == null
     select new {
      Name = c.Name, Caption = c.Caption,
      Children = 
      from d in BizCategories
      where d.ParentID == c.BizCatID && d.Bizs.Count() > 0
      select d
     }

I should be able run another LINQ query over these results and pull out exactly what I need. Not at a computer where I can test that now, but will reply once I can. Thanks!

Answer 3

create classes to hold your information like so

public class BusinessCat
{
    public string Name{get;set;}
    public string Caption{get;set;}
    public List<'dunno datatype'> Children{get;set;};
}

var results = from c in BizCategories
    where c.ParentID == null
     select new BusinessCat{
      Name = c.Name,
      Caption = c.Caption,
      Children =  (from d in BizCategories
        where d.ParentID == c.BizCatID && d.Bizs.Count() > 0 select d).ToList()
     }

and with this you have a list full of Children and you can simply iterate through it with a foreach.

You can also do .Join() extension method for

where d.ParentID == c.BizCatID && d.Bizs.Count()