Question

I am developing a windows mobile app. Right now I am just testing that it can correctly query the local SQL Server CE database. It works fine until I put a WHERE statement in.

Here is my code:

private void buttonStart_Click(object sender, EventArgs e)
{
   System.Data.SqlServerCe.SqlCeConnection conn = new System.Data.SqlServerCe.SqlCeConnection(
   ("Data Source=" + (System.IO.Path.Combine(System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase), "ElectricReading.sdf") + ";Max Database Size=2047")));

   try
   {
       // Connect to the local database
       conn.Open();
       System.Data.SqlServerCe.SqlCeCommand cmd = conn.CreateCommand();

       SqlCeParameter param = new SqlCeParameter();
       param.ParameterName = "@Barcode";
       param.Value = "%" + textBarcode.Text.Trim() + "%";

       // Insert a row
       cmd.CommandText = "SELECT * FROM Main2 WHERE Reading LIKE @Barcode";
       cmd.Parameters.Add(param);

       cmd.ExecuteNonQuery();

       DataTable data = new DataTable();

       using (SqlCeDataReader reader = cmd.ExecuteReader())
       {
           if (reader.Read())
           {
              data.Load(reader);
           }
       }

       if (data != null)
       {
           this.dataGrid1.DataSource = data;
       }
   }
   finally
   {
       conn.Close();
   }

The database contains this data:

Okay so you can see I changed the WHERE statement to use the Reading column just for testing purposes. When I enter “111” into the textbox and run –> it returns only the row where reading ="1111" and not the row that contains “111”.

If I enter “1111” it does not return any data.

If I enter “1” it will return both the “1111” row and the “111” row which is the correct behavior.

However if I enter “11” it once again only returns the “1111” row.

Any other data entry of 2’s or 9’s attempting to return those rows does not work.

I’m not sure what is going on? This does not make any sense. It is not behaving like I would expect in any way shape or form. I know this must be a little confusing to read. I hope it makes enough sense to get some answers. Please help!

NOTE: I added the “%” before and after the text in an attempt to get better results. This is not desired.

EDIT <<<———————–I did have Reading = @Barcode, I just accidently typed Location for this question, that is not the problem.

Answer 1

Firstly, some things to note:

1) As other commentators have noted, use the Reading column, not the Location column. I know you have mentioned you are testing, but swapping around column names and then changing code isn’t the easiest way to troubleshoot these things. Try to only change one thing at a time.

2) If Reading is numeric, you are going to have to convert the column value first.

So your query becomes:

"SELECT * FROM Main2 WHERE CONVERT(varchar, Reading) LIKE @Barcode";

Also see How to use parameter with LIKE in Sql Server Compact Edition for more help with working with parameters in SqlServerCE.

3) Set a parameter type on your SqlCEParameter. I’ve linked to the appropriate page in the code example below.

4) You are using ExecuteNonQuery for no reason. Just get rid of it in this context. It’s for when you want to make a change to the database (like an insert, update, delete) or execute something (like a stored proc that can also insert, update, delete etc) that returns no rows. You’ve probably cut and paste this code from another place in your app 🙂

5) Use using on disposable objects (see example below). This will make managing your connection lifecycle much simpler. It’s also more readable (IMO) and will take care of issues when exceptions occur.

6) Use the using statement to import the BCL (Base Class Libraries) into your current namespace:

Add the following using statements to the top of your class (.cs). This will make using all of the .Net classes a lot simpler (and is much easier to read and less wear on your keyboard 😉

using System.Data.SqlServerCe;
using System.IO;
using System.Reflection;

A more complete example would look like the following

private void buttonStart_Click(object sender, EventArgs e) 
{ 
   using(SqlCeConnection conn = new SqlCeConnection( 
   ("Data Source=" + (Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().GetName().CodeBase), "ElectricReading.sdf") + ";Max Database Size=2047"))))
   {

       // Connect to the local database 
       conn.Open(); 
       using(SqlCeCommand cmd = conn.CreateCommand())
       {
       SqlCeParameter param = new SqlCeParameter(); 
       param.ParameterName = "@Barcode"; 
       param.DBType = DBType.String; //Intellisense is your friend here but See http://msdn.microsoft.com/en-US/library/system.data.sqlserverce.sqlceparameter.dbtype(v=VS.80).aspx for supported types
       param.Value = "%" + textBarcode.Text.Trim() + "%"; 

       // SELECT rows
       cmd.CommandText = "SELECT * FROM Main2 WHERE CONVERT(varchar, Reading) LIKE @Barcode";
       cmd.Parameters.Add(param); 

       //cmd.ExecuteNonQuery();  //You don't need this line

       DataTable data = new DataTable(); 

       using (SqlCeDataReader reader = cmd.ExecuteReader()) 
       { 
          data.Load(reader); //SqlCeDataReader does not support the HasRows property.
          if(data.Rows.Count > 0)
          {
              this.dataGrid1.DataSource = data;
          } 
       } 

       }
   }


} 

Intellisense should be able to clean up any errors with the above but feel free to ask for more help.

Finally, you also might be able to set the data source of the grid directly to a datareader, try it!

       using (SqlCeDataReader reader = cmd.ExecuteReader()) 
       { 
          dataGrid1.DataSource = reader; 
       } 

You can then get rid of the DataTable.