Question

RESOLVED..

This has been resolved as I was making a stupid mistake. I didn’t initialize the string builder
StringBuilder sb = new StringBuilder();

I am using the following CTE query in my website to fetch data using c#. But it is giving an error in the if Statement inside for loop

ERROR MESSAGE

System.NullReferenceException was unhandled by user code
Message=Object reference not set to an instance of an object.

    String strSqlCTE;

    strSqlCTE= " DECLARE @PageId int ";
    strSqlCTE += " SET @PageId =" + pageid + "; ";
    strSqlCTE += " WITH RecursiveTable (PageId, PageName, PageInternalLink, PageInternalLinkUrl, PageInheritance, Level) ";
    strSqlCTE += " AS(SELECT      tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance,  0 AS Level ";
    strSqlCTE += " FROM pg_Pages AS tt WHERE PageId = @PageId ";
    strSqlCTE += " UNION ALL ";
    strSqlCTE += " SELECT tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance, Level + 1 ";
    strSqlCTE += " FROM pg_Pages AS tt ";
    strSqlCTE += " INNER JOIN RecursiveTable rt ON rt.PageInheritance = tt.PageId  ) ";
    strSqlCTE += " SELECT * FROM RecursiveTable ORDER BY Level DESC ";

    DataSet dsBC = new DataSet();
    dsBC = DataProvider.Connect_Select(strSqlCTE);
    if (dsBC.Tables[0].Rows.Count > 0)
    {
        int RowCount = dsBC.Tables[0].Rows.Count;
        StringBuilder sb = null;
        for ( int i = 0; i <= RowCount; i++)
        {
            if (i == RowCount)
            {
                sb.Append("<a href='" + dsBC.Tables[0].Rows[0]["PageInternalLinkUrl"].ToString() + "'>" + dsBC.Tables[0].Rows[0]["PageName"].ToString().ToUpper() + "</a>");
            }
            else
            {
                sb.Append("<a href='" + dsBC.Tables[0].Rows[0]["PageInternalLinkUrl"].ToString() + "'></a> ● ");
            }

        }

        ltrBreadCrumb.Text = sb.ToString();

    }

My CTE query is is working and below is the actual query

DECLARE @PageId int
SET @PageId = 31;
WITH RecursiveTable (PageId, PageName, PageInternalLink, PageInternalLinkUrl, PageInheritance, Level)
AS(
   --Anchor
    SELECT      tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance,  0 AS Level
    FROM pg_Pages AS tt
    WHERE PageId = @PageId
    UNION ALL
   --Recursion
    SELECT tt.PageId,  tt.PageName , tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance, Level + 1
    FROM pg_Pages AS tt
    INNER JOIN RecursiveTable rt ON rt.PageInheritance = tt.PageId
)
SELECT * FROM RecursiveTable ORDER BY Level DESC

This works good on when run in the Management studio but following statement generate error

sb.Append("<a href='" + dsBC.Tables[0].Rows[0]["PageInternalLinkUrl"].ToString() + "'></a> ● ");

dsBC.Tables[0].Rows.Count statement return correct row numbers based on the input. Problems seems to be in the as it cant recognize column name which is present in the CTE query.

Am I am doing something wrong please correct me about the problem.

Answer 1

This has been resolved as I was making a stupid mistake. I missed to initialize string builder

StringBuilder sb = new StringBuilder();

String strSqlCTE;

    strSqlCTE= " DECLARE @PageId int ";
    strSqlCTE += " SET @PageId =" + pageid + "; ";
    strSqlCTE += " WITH RecursiveTable (PageId, PageName, PageInternalLink, PageInternalLinkUrl, PageInheritance, Level) ";
    strSqlCTE += " AS(SELECT      tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance,  0 AS Level ";
    strSqlCTE += " FROM pg_Pages AS tt WHERE PageId = @PageId ";
    strSqlCTE += " UNION ALL ";
    strSqlCTE += " SELECT tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance, Level + 1 ";
    strSqlCTE += " FROM pg_Pages AS tt ";
    strSqlCTE += " INNER JOIN RecursiveTable rt ON rt.PageInheritance = tt.PageId  ) ";
    strSqlCTE += " SELECT * FROM RecursiveTable ORDER BY Level DESC ";

    DataSet dsBC = new DataSet();
    dsBC = DataProvider.Connect_Select(strSqlCTE);
    if (dsBC.Tables[0].Rows.Count > 0)
    {
        int RowCount = dsBC.Tables[0].Rows.Count;
        StringBuilder sb = new StringBuilder();
        for ( int i = 0; i <= RowCount; i++)
        {
            if (i == RowCount)
            {
                sb.Append("<a href='" + dsBC.Tables[0].Rows[i]["PageInternalLinkUrl"].ToString() + "'>" + dsBC.Tables[0].Rows[i]["PageName"].ToString().ToUpper() + "</a>");
            }
            else
            {
                sb.Append("<a href='" + dsBC.Tables[0].Rows[i]["PageInternalLinkUrl"].ToString() + "'></a> ● ");
            }

        }

        ltrBreadCrumb.Text = sb.ToString();

    }