Question

I am busted with a weird bug in my app. It comes in levels or error messages:

1. There is already and open datareader associated.
   Then comes
2. Invalid attempt to call Read when reader is closed.
   Then comes
3. Index was outside the bounds of the array.
   Then comes
4. Specified cast is not valid.

Let me explain first what’s my code is doing:
I am using Repository Pattern for my Linq-Sql app. From that repository I calling this method

 internal static IEnumerable<ParentChild> GetAllCategoriesAndSubcategories()
        {
            lock (Context) // lock is implemented just before asking question, to check whether it can solve the issue or not...
            {
                return from p in Context.Categories
                       let relatedchilds = (from c in Context.SubCategories
                                            where c.CategoryId == p.Id
                                            select c).Take(5)
                       select new ParentChild
                       {
                           Parent = p,
                           Childs = relatedchilds
                       };
            }

        }

This method is picking rows from two tables, Parent and Child and return the result as a new collection of class

public class ParentChild
    {
        public Category Parent { get; set; }
        public IEnumerable<SubCategory> Childs { get; set; }
    }

Sometimes it works fine but when the traffic increases and concurrency then in that case i start getting these errors. Coming to the issue, From UI i am consuming IEnumerable<ParentChild> GetAllCategoriesAndSubcategories() to display it in heirarchy.

At UI i am using this method to render the text:

 /// <summary>
        /// Write categories Jquery html to the Category usercontrol
        /// </summary>
        private void WriteCategories()
        {

            // retrieves all categories and its subcategories as a generic list of ParentChild
            var dt = CategoryRepository.GetAllCategoriesAndSubcategories();

            //Conversion of dynamic jquery html string starts here
            var sb = new StringBuilder();
            sb.AppendLine(" <div class='widget_box' id='category'>");
            sb.AppendLine("     <div class='wintitle'>");
            sb.AppendLine("         <div class='inner_wintitle'>Categories</div>");
            sb.AppendLine("     </div>");
            sb.AppendLine("     <div class='winbody'>");
            sb.AppendLine("         <ul class='categories'>");
            var i = 1;
            foreach (ParentChild item in dt) //<--* BUGGY PART*
            {
                sb.AppendLine(
                    string.Format("<li class='catetitle' id='catetitle{0}'><a href='subcategory.aspx?cid={1}&cname={2}'>{2}</a></li>", i,
                                  item.Parent.Id, item.Parent.Name));
                sb.AppendLine(
                    string.Format("<li style='display:none;' class='category_sub' id='subcategory{0}' ><div><ul>", i));
                foreach (var subCategory in item.Childs)
                {
                    sb.AppendLine(string.Format("<li><a href='subcategory.aspx?cid={0}&cname={1}&scid={2}&scname={3}'>{3}</a></li>", item.Parent.Id,
                                                item.Parent.Name, subCategory.Id, subCategory.Name));
                }
                sb.AppendLine(
                    string.Format(
                        "<li class='catetitle' id='catetitle{0}'><a href='subcategory.aspx?cid={1}&cname={2}'>View all categories</a></li>",
                        i, item.Parent.Id, item.Parent.Name));
                sb.AppendLine("</ul></div></li>");
                i++;
            }
            sb.AppendLine("</div></ul></div>");
            //Conversion of dynamic jquery html string ends here

            // javascript function to display the subcategories when mouse is hovered to the category
            sb.AppendLine("<script type='text/javascript'>init_categories();</script>");
            ucCategories1.CategoryHtml = sb.ToString(); // Generated text is finally set to the usercontrols property.
        }

I am getting the bug @ foreach (ParentChild item in dt). Please help me.

Suggestion Required:
I am using this as my repo pattern implementation:

 internal sealed class LeadsRepository : IRepository<BuySell>
    {
        private static readonly BusinessBazaarDataContext Context;

        static LeadsRepository()
        {
            Context = new BusinessBazaarDataContext();
        }
}

I don’t thinks its a good way to use Datacontext. Please suggest me… Thanks

Answer 1

Switch to List<ParentChild> and return a fully populated List from your GetAllCategoriesAndSubcategories. Your lock would then be doing what you intende (so I assume).

Specifically, you need to do:

internal static IList<ParentChild> GetAllCategoriesAndSubcategories()
    {
        lock (Context) // lock is implemented just before asking question, to check whether it can solve the issue or not...
        {
            return (from p in Context.Categories
                   let relatedchilds = (from c in Context.SubCategories
                                        where c.CategoryId == p.Id
                                        select c).Take(5)
                   select new ParentChild
                   {
                       Parent = p,
                       Childs = relatedchilds
                   }).ToList();
        }

    }