Speed Performance In Recursive SQL Requests

Question

Hi,

I have so category and this categories have unlimited sub category. In Database Table, Fields are ID, UpperID and Title.

If I call a category and its subcategory in DataTable with recursive method in program(ASP.NET project) performance is very bad. And many user will use this application so everything goes bad. Maybe All categories Fill to A Cache object and then we musnt go to Database. But category count is 15000 or 20000. So I think isn't a good method.

What can I do for fast performance? Are you give me any suggestion?

Answer 1

caching or other in-memory-persistance is by far better than doing this on a relational system :) ... hey... it's oop!

just my 2 cents!

eg.

var categories = /* method for domain-objects*/.ToDictionary(category => category.ID);
foreach (var category in categories.Values)
{
    if (!category.ParentCategoryID.HasValue)
    {
        continue;
    }
    Category parentCategory;
    if (categories.TryGetValue(category.ParentCategoryID.Value, out parentCategory))
    {
        parentCategory.AddSubCategory(category);
    }
}

et voila ... your tree is ready to go!

edit:
do you exactly know where your performance bottle-neck is?...

to give you some ideas, eg:

• loading from database
• building up the structure
• querying the structure

loading from database:
then you should load it once and be sure to have some changetracking/notifying to get changes (if made) or optimize your query!

building up the structure:
the way i create the tree (traversal part) is the wastest you can do with a Dictionary<TKey, TValue>

querying the structure:
the structure i've used in my example is faster than List<T>. Dictionary<TKey, TValue> uses an index over the keys - so you may use int for the keys (IDs)

edit:

So you use DataTable to fix the problem. Now you've got 2 problems: me and DataTable

what do you have right now? where are you starting from? can you determine where your mudhole is? give us code!

Answer 2

Thanks All,

I find my solution with Common Table Expressions(CTE) fifty- fifty. Its allow fast recursive queries.

WITH CatCTE(OID, Name, ParentID) 
AS 
( 
   SELECT OID, Name, ParentID FROM Work.dbo.eaCategory
   WHERE OID = 0   
       UNION ALL 
   SELECT C.OID, C.Name, C.ParentID FROM Work.dbo.eaCategory  C JOIN CatCTE as CTE ON C.ParentID= CTE.OID
) 
SELECT * FROM CatCTE