No rows found, C# using OleDB

Question

I have been rewriting a C# program to better encapsulate accessing an Access database, using OleDb. It runs, but doesn't find the row that exists, but running the SQL query in Access does find it.

The question is: what is wrong with my code? Why don't I get any rows returned?

I'm using VS 2017 and Access 2013. The PC is an up-to-date windows 10 x64 machine.

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.OleDb;
using System.Linq;

namespace OleDbTest
{
    class Program
    {
        static void Main( string[] args )
        {
            // Create Profile File object
            ProcessEJFile EJP = new ProcessEJFile(
                "Provider=Microsoft.ACE.OLEDB.12.0;" +
                @"Data Source=E:\Users\sallyw\Documents\Bar.accdb;" +
                "Persist Security Info=False;");

            // Get details of last header - this should return just one row
            string query = 
            //      @"select * from stock_head where sh_ref in ( select max( stock_head.[ sh_ref ] ) FROM stock_head WHERE sh_ref like ""[#]%"")";

                    "select sh_id, sh_ref, sh_lineno, sh_type, sh_supplier, sh_datetime from stock_head where sh_id = 19;";

            //      "select * from stock_head where sh_ref = 19;"

            List<StockHead> shlist = EJP.GetStockHead(query, null );
            if ( shlist == null )
            {
                Console.WriteLine( "shlist is null" );
            }
            else
            {
                Console.WriteLine( "shlist contains {0} entries", shlist.Count );
            }
            Console.ReadLine();
        }
    }

    class ProcessEJFile
    {
        AccessDatabase Accdb = null;

        public ProcessEJFile( string connectionString )
        {
            Accdb = new AccessDatabase( connectionString );
            Console.WriteLine( "ProfessEJFile #1 - connection string = {0}", connectionString );
        }

        public List<StockHead> GetStockHead( string sql, params object[] args )
        {
            DataTable t;
            if ( args == null )
            {
                Console.WriteLine( "GetStockHead #1 - args are NULL " );
            }
            else
            {
                Console.WriteLine( "GetStockHead #2 - {0} arguments passed", args.Count() );
            }

            Accdb.ExecuteQuery( out t, sql, args );

            if ( t != null )
            {
                List<StockHead> shlist = new List<StockHead>();

                foreach ( DataRow r in t.Rows )
                {
                    Console.WriteLine( t.ToString() );
                    //StockHead sh = new StockHead(
                    //    (int)r["sh_id"],
                    //    (string)r["sh_ref"],
                    //    (int)r["sh_lineno"],
                    //    (string)r["sh_type"],
                    //    (string)r["sh_supplier"],
                    //    (DateTime)r["sh_datetime"]);
                    //shlist.Add( sh );
                }
                return shlist;
            }
            else
            {
                Console.WriteLine( "GetStockHead #3 - t is null" );
                return null;
            }
        }
    }
    class AccessDatabase
    {
        public OleDbConnection conn = new OleDbConnection();

        public AccessDatabase( string connection )
        {
            conn.ConnectionString = connection;
        }

        public bool OpenDatabase()
        {
            try
            {
                conn.Open();
            }
            catch ( Exception ex )
            {
                Console.WriteLine( "OpenDatabase()\n" + ex.Message );
                return false;
            }
            return true;
        }

        public void CloseDatabase()
        {
            if ( conn == null )
                return;

            conn.Close();
        }

        public void ExecuteQuery( out DataTable dataTable, string sql, params object[] args )
        {
            dataTable = new DataTable();
            string query;

            // Simplified version not validating or cleaning arguments in any way
            if (args == null )
            {
                query = sql;
            }
            else
            {
                query = string.Format( sql, args );
            }
            Console.WriteLine( "ExecuteQuery #3 - query = '{0}'", query );

            if ( OpenDatabase() )
            {
                OleDbCommand command = new OleDbCommand( query, conn );
                OleDbDataAdapter adapter = new OleDbDataAdapter( command );
                adapter.Fill( dataTable );
            }
            else
            {
                Console.WriteLine( "ExecuteQuery #9 - cannot open database" );
            }
        }
    }

    class StockHead
    {
        public int sh_id;              // autonumber
        public string sh_ref;          // short text
        public int sh_lineno;          // Number
        public string sh_type;         // short text
        public string sh_supplier;     // short text
        public DateTime sh_datetime;   // date/time

        public StockHead( int id, string refno, int lineno, string type, string supplier, DateTime datetime )
        {
            sh_id = id;
            sh_ref = refno;
            sh_lineno = lineno;
            sh_type = type;
            sh_supplier = supplier;
            sh_datetime = datetime;
        }
    }
}

Data in CSV format, class stock_head shows the Access column types:

1,"#000001",,"IR","INITIAL RESET",20/8/2013 08:33:00
2,"#000002",,"SD","FORMATTING",20/8/2013 08:34:00
3,"#000003",,"SD","FOLDER CREATE",20/8/2013 08:35:00
4,"#000004",,"SD","FOLDER SELECT",20/8/2013 08:35:00
5,"#000005",,"NS","NO SALE",20/8/2013 11:14:00
6,"#000006",,"NS","NO SALE",20/8/2013 11:46:00
7,"#000007",,"NS","NO SALE",20/8/2013 12:16:00
8,"#000008",,"SALE",,20/8/2013 15:11:00
9,"#000009",,"SALE",,20/8/2013 15:30:00
10,"#000010",,"Z1",,20/8/2013 15:32:00
11,"#000011",,"NS","NO SALE",20/8/2013 15:32:00
12,"#000012",,"SALE",,20/8/2013 16:46:00
13,"#000013",,"SALE",,20/8/2013 16:47:00
14,"#000014",,"SALE",,20/8/2013 17:32:00
15,"#000015",,"Z1",,20/8/2013 19:25:00
16,"#000016",,"NS","NO SALE",20/8/2013 19:25:00
17,"#000017",,"Z1",,20/8/2013 21:52:00
18,"#000018",,"NS","NO SALE",20/8/2013 21:52:00
19,"#000019",,"SALE",,23/8/2013 18:27:00
20,"#000020",,"SALE",,23/8/2013 19:06:00
21,"#000021",,"SALE",,23/8/2013 20:24:00
22,"#000022",,"SALE",,23/8/2013 20:36:00
23,"#000023",,"SALE",,23/8/2013 21:21:00
24,"#000024",,"SALE",,23/8/2013 21:57:00
25,"#000025",,"SALE",,23/8/2013 22:38:00
26,"#000026",,"Z1",,23/8/2013 22:40:00
27,"#000027",,"NS","NO SALE",23/8/2013 22:40:00
28,"#000028",,"SALE",,24/8/2013 16:09:00
29,"#000029",,"SALE",,24/8/2013 16:28:00
30,"#000030",,"SALE",,24/8/2013 16:58:00

Answer 1

If I alter the code creating a StockHead object to use literals instead of the correct values it works. There must be an elegant way of resolving this!

                StockHead sh = new StockHead(
                    (int)r[ "sh_id" ],
                    (string)r[ "sh_ref" ],
                    0,                          //(int)r[ "sh_lineno" ],
                    (string)r[ "sh_type" ],
                    "",                         //(string)r[ "sh_supplier" ],
                    (DateTime)r[ "sh_datetime" ]);

Answer 2

OK found a fix by amending the StockHead constructor to take the DataRow rather than individual arguments, and checking for any nulls there.

Is it a good way? Is there a better way? In a way I like it more as the complications are more tucked away - the line that calls it is now simply

StockHead sh = new StockHead( r );

Constructor code is now:

    public StockHead( DataRow row )
    {
        this.sh_id = (int)row[ "sh_id" ];
        this.sh_ref = (string)row[ "sh_ref" ];
        if ( !string.IsNullOrEmpty( row[ "sh_lineno" ].ToString() ) )
        {
            this.sh_lineno = (int)row[ "sh_lineno" ];
        }
        this.sh_type = (string)row[ "sh_type" ];
        if ( !string.IsNullOrEmpty( row[ "sh_lineno" ].ToString() ) )
        {
            this.sh_supplier = (string)row[ "sh_supplier" ];
        }
        this.sh_datetime = (DateTime)row[ "sh_datetime" ];
    }

Answer 3

This is simple to be edit GetStockHead function

public List<StockHead> GetStockHead( string sql, params object[] args )
{
    DataTable t;
    if ( args == null )
    {
        Console.WriteLine( "GetStockHead #1 - args are NULL " );
    }
    else
    {
        Console.WriteLine( "GetStockHead #2 - {0} arguments passed", args.Count() );
    }

    Accdb.ExecuteQuery( out t, sql, args );

    if ( t != null )
    {
        List<StockHead> shlist = new List<StockHead>();

        foreach ( DataRow r in t.Rows )
        {
            Console.WriteLine( t.ToString() );
            StockHead sh = new StockHead(
                (int)r["sh_id"],
                (string)r["sh_ref"],
                (int)r["sh_lineno"],
                (string)r["sh_type"],
                (string)r["sh_supplier"],
                (DateTime)r["sh_datetime"]);
            shlist.Add( sh );
        }
        return shlist;
    }
    else
    {
        Console.WriteLine( "GetStockHead #3 - t is null" );
        return null;
    }
}