Re: Using datareader instead of dataset

[Joel Cochran <jrc@xxxxxxxxxx>]

On Fri, 2005-06-10 at 13:12, Rohan Sootarsing wrote:
> This is what ive tried so far but i am getting an error saying not all
> code paths return a value

Well, I hate to point out the obvious... but not all your paths return a
value...

And this has nothing to do with the DataReader, but rather basic C#
language stuff: 

The method returns a string, therefore EVERY possible exit path for the
method must issue a return string.  In this case, you have defined the
return string inside a try block!  Define the string OUTSIDE the try
block, set an initial value, and then adjust it's value inside the try
block.  Then, make the return statement is the last statement in the
method.

And this below cannot be the entire method... if it is, then you have no
catch block for your try block, which I don't think will compile, and if
it will would be entirely useless.

HTH,

Joel Cochran
http://www.rpgnext.com

> [WebMethod]
> public string CTX(string filter)
> {
>   try
>   {
>       string result = "Nothing";
>       iDB2Connection cn = new
> iDB2Connection("Datasource=TDC01;userid=RDS;password=sootarsing;DefaultCollection=QGPL;");
>       cn.Open();
>       string sqlstmt = "Select * from ctx4nthg where REF
> ='"+@filter+"'";
>       iDB2Command cmd = new iDB2Command(sqlstmt,cn);
>       iDB2DataReader dr = cmd.ExecuteReader();
>       while (dr.Read())
>       {
>       result = dr.GetString(0);
>       }
>                               
>                return result;
> 
> >>> jrc@xxxxxxxxxx 10/06/2005 09:07:52 >>>
> On Fri, 2005-06-10 at 09:44, Rohan Sootarsing wrote:
> > Hi I am Using a dataset to return data but want to convert this to
> > datareader but can't find much doumentation can anyone help me here
> is
> > my current code
> > 
> > 
> > iDB2Connection connDB2=new iDB2Connection(
> >   "DataSource=TDC01;" +
> >   "userid=RDS;password=sootarsing;DefaultCollection=QGPL;");
> > DataSet ds = new DataSet();
> > iDB2DataAdapter adpt = new iDB2DataAdapter();
> > string szSQLstmt = "Select * from ctx4nthg where REF ='"
> +@filter+"'";
> > adpt.SelectCommand = new iDB2Command(szSQLstmt,connDB2);
> > adpt.Fill(ds);
> > return ds;
> 
> DataReader is very simple to use:
> 
> <code>
> [create the connection and SQL string as above...]
> iDB2Command cmd = new iDB2Command( sqSQLstmt , connDB2 );
> iDB2DataReader reader = cmd.ExecuteReader();
> while ( reader.Read() )
> {
>       // Process the row
> }
> reader.Close();
> </code>
> 
> Some notes for use: 
> 1) A DataReader has an active database connection, which means it will
> stay open until you close it.  (This is unlike a DataSet which is
> disconnected).  As a rule of thumb, issue the .Close() method as soon
> as
> possible.
> 
> 2) To obtain the field data from the current row, you access it like
> an
> array variable, using either the field name or the index number
> (0-based):
> 
>       string field1 = (string)reader[ "FIELD1" ];
>       // or
>       string field1 = (string)reader[ 0 ];
> 
> If you don't know the index numbers, you can retrieve them by using
> the
> GetOrdinal() method:
> 
>       int field1Ordinal = reader.GetOrdinal( "FIELD1" );
> 
> Performance will be much better using ordinal values, so I typically
> capture the ordinals outside the loop and then use them to access the
> fields:
> 
> <code>
> iDB2Command cmd = new iDB2Command( sqSQLstmt , connDB2 );
> iDB2DataReader reader = cmd.ExecuteReader();
> 
> int field1Ordinal = reader.GetOrdinal( "FIELD1" );
> int field2Ordinal = reader.GetOrdinal( "FIELD2" );
> int field3Ordinal = reader.GetOrdinal( "FIELD3" );
> while ( reader.Read() )
> {
>       string field1 = (string)reader[ field1Ordinal ];
>       int field2 = (int)reader[ field2Ordinal ];
>       string field3 = (string)reader[ field3Ordinal ];
> }
> reader.Close();
> </code>
> 
> 3. Finally, if you are retrieving a single field, look at
> ExecuteScalar
> - it should be lightning fast.
> 
> Hope this helps,
> 
> Joel Cochran
> http://www.rpgnext.com
> 
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