SQL DataReader missing a row in loop

Question

When running the following code it leaves out one row. When I do a files.Count it says there are 4 rows but there is no data stored for the 4th row. When I run the stored procedure from within SQL Manager it returns all 4 rows and all the data. Any help?

            List<File> files = new List<File>();
            SqlConnection active_connection = new SqlConnection(m_connection_string);
            SqlCommand cmd = new SqlCommand();
            SqlDataReader dr = null;

            try
            {
                active_connection.Open();
                cmd.Connection = active_connection;
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.CommandText = "dalsp_Select_Organization_Files";

                SqlParameter param;

                param = cmd.Parameters.Add("@p_organization_guid", SqlDbType.UniqueIdentifier);
                param.Value = new Guid(organization_guid);

                param = cmd.Parameters.Add("@p_file_type", SqlDbType.NVarChar, 50);
                param.Value = file_type;

                dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);

                if (dr.HasRows)                    
                {                    
                    while (dr.Read())
                    {
                        File file = new File();
                        file.OrganizationGuid = dr["OrganizationGuid"].ToString();
                        file.FileGuid = dr["FileGuid"].ToString();
                        file.FileLocation = dr["FileLocation"].ToString();
                        file.FileName = dr["FileName"].ToString();
                        file.FileType = (FileTypeEnum)Enum.Parse(typeof(FileTypeEnum), dr["FileType"].ToString());
                        file.FileExtension = dr["FileExtension"].ToString();
                        file.FileDescription = dr["FileDescription"].ToString();
                        file.ThumbnailPath = dr["ThumbnailPath"].ToString();
                        files.Add(file);
                    }       
                }
                dr.Close();
                dr = null;

                active_connection.Close();
                cmd = null;

            }
            catch (Exception)
            {
                throw;
            }
            finally
            {
                if (active_connection.State != ConnectionState.Closed)
                {
                    active_connection.Close();
                    active_connection.Dispose();
                }
            }

            return files;

Answer 1

Have you tried stepping through this in a debugger, and checking your command params before you exec the reader? Do you get the same values in the result set as when you run the sproc direct on sql?

I could be wrong, cos there are a few ways of doing this, but something looks a little screwy in the way you are adding the params to the command.

I usually use a pattern more like:

SqlParameter param = new SqlParameter();  
// set param stuff - here or in ctor   
cmd.Parameters.Add(param);

Is largely about what works for you....

Most of the times that I have had problems with sprocs is when I pooched the parameters.

Answer 2

If you are saying your files collection has 4 items, but the 4 item contains no value, what do you mean by that? Is it null, does the object have no data, or does it throw an index out of range exception?

Are you doing a files[4] or something like the following?

for(int x = 1; x < files.length; x++)
{
     files[x]
}

That won't work. Remember 0 based indexing in C#.

As a side note, you could do away with your try catch statments by doing something like:

using (SqlConnection connection = new SqlConnection(conn_string))
{
    connection.Open();
    using (SqlCommand cmd = new SqlCommand("SELECT * FROM MyTable", connection))
    {
         using (SqlDataReader dr = cmd.ExecuteReader())
         {
             return result;
         }
    }
}

The using statement will guarantee disposal (and therefore the closing) of the reader and connection.

Answer 3

The code looks correct to me. I think you'd definitely want to step through a debugger to see how many rows are returned from ExecuteReader. One comment I have is that the "if (dr.HasRows)" is kinda redundant since the "while (dr.Read())" will give you the same effect.

Another question I would have is do you know if you are missing the first or last record?

Brian

Answer 4

You should ditch "if (dr.HasRows)", all it does is duplicate the check in the while loop.

You shouldn't ever be calling Close on a connection, nor should you set it to null. Instead you should wrap the connection in a "using" block like so:

using (SqlCommand cmd = new SqlCommand()) {
   //use the connection
}

The same can be said for you data reader and SQL Command.

This next bit does nothing at all, delete it.

  catch (Exception) { throw; }