C# 4 and .NET 4

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Here, the definition of the parameters is much more complex. The second parameter, @RegionID, is defined
to include its parameter direction, which in this example is Output. In addition to this flag, on the last line
of the code, the UpdateRowSource enumeration is used to indicate that data will be returned from this
stored procedure via output parameters. This flag is mainly used when issuing stored procedure calls from a
DataTable (which is discussed later in this chapter).
Calling this stored procedure is similar to the previous examples, except in this instance the output
parameter is read after executing the procedure:
cmd.Parameters["@RegionDescription"].Value = "South West";
cmd.ExecuteNonQuery();
int newRegionID = (int) cmd.Parameters["@RegionID"].Value;
After executing the command, the value of the @RegionID parameter is read and cast to an integer. A
shorthand version of the preceding is the ExecuteScalar() method, which will return (as an object) the
first value returned from the stored procedure.
You might be wondering what to do if the stored procedure you call returns output parameters and a set of
rows. In this instance, define the parameters as appropriate, and rather than calling ExecuteNonQuery(),
call one of the other methods (such as ExecuteReader()) that will permit you to traverse any record(s)
returned.
fasT daTa aCCess: The daTa reader
A data reader is the simplest and fastest way of selecting some data from a data source, but it is also the
least capable. You cannot directly instantiate a data reader object — an instance is returned from the
appropriate database’s command object (such as SqlCommand) after having called the ExecuteReader()
method.
The following code demonstrates how to select data from the Customers table in the Northwind
database. The example connects to the database, selects a number of records, loops through these selected
records, and outputs them to the console.
This example uses the OLE DB provider as a brief respite from the SQL provider. In most cases,
the classes have a one-to-one correspondence with their SqlClient cousins; for example, there is the
OleDbConnection object, which is similar to the SqlConnection object used in the previous examples.
To execute commands against an OLE DB data source, the OleDbCommand class is used. The following
code shows an example of executing a simple SQL statement and reading the records by returning an
OleDbDataReader object.
Note the second using directive, which makes the OleDb classes available:
using System;
using System.Data.OleDb;
Most of the data providers currently available are shipped within the same assembly, so it is only necessary
to reference the System.Data.dll assembly to import all classes used in this section.
public class DataReaderExample
{
public static void Main(string[] args)
{
string source = "Provider=SQLOLEDB;" +
"server=(local);" +
"integrated security=SSPI;" +
"database=northwind";
string select = "SELECT ContactName,CompanyName FROM Customers";
OleDbConnection conn = new OleDbConnection(source);
conn.Open();
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