C# 4 and .NET 4

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The < p r o v i d e r > C ommand classes have a property called CommandType , which is used to defi ne whether the
command is a SQL clause, a call to a stored procedure, or a full table statement (which simply selects all
columns and rows from a given table). The following table summarizes the CommandType enumeration.
CommandTyPe
Text (default)
StoredProcedure
TableDirect
eXamPle
String select = “SELECT ContactName FROM Customers”;SqlCommand
cmd = new SqlCommand(select, conn);
SqlCommand cmd = new SqlCommand(“CustOrderHist”, conn);cmd
.CommandType = CommandType.StoredProcedure;cmd.Parameters
.AddWithValue(“@CustomerID”, “QUICK”);
OleDbCommand cmd = new OleDbCommand(“Categories”, conn);cmd
.CommandType = CommandType.TableDirect;
When executing a stored procedure, it might be necessary to pass parameters to that procedure. The
previous example sets the @CustomerID parameter directly, although there are other ways of setting
the parameter value, which you look at later in this chapter. Note that since .NET 2.0, the AddWithValue()
method is included in the command parameters collection — and the Add(name, value) member was
attributed as Obsolete . If you have used this original method of constructing parameters for calling a
stored procedure, you will receive compiler warnings when you recompile your code. We suggest altering
your code now because Microsoft will most likely remove the older method in a subsequent release of .NET.
The TableDirect command type is valid only for the OleDb provider; other providers
will throw an exception if you attempt to use this command type with them.
executing Commands
After you have defi ned the command, you need to execute it. A number of ways exist to issue the statement,
depending on what you expect to be returned (if anything) from that command. The C o m m a n d
classes provide the following execute methods:
➤
➤
➤
ExecuteNonQuery() — Executes the command but does not return any output
ExecuteReader() — Executes the command and returns a typed IDataReader
ExecuteScalar() — Executes the command and returns the value from the fi rst column of the fi rst
row of any result set
In addition to these methods, the SqlCommand class exposes the following method:
➤
executenonQuery()
ExecuteXmlReader() — Executes the command and returns an XmlReader object, which can be
used to traverse the XML fragment returned from the database
The ExecuteNonQuery() method is commonly used for UPDATE , INSERT , or DELETE statements, where the
only returned value is the number of records affected. This method can, however, return results if you call a
stored procedure that has output parameters:
using System;
using System.Data.SqlClient;
public class ExecuteNonQueryExample
{
public static void Main(string[] args)
{
string source = "server=(local);" +
"integrated security=SSPI;" +
"database=Northwind";
string select = "UPDATE Customers " +
"SET ContactName = 'Bob' " +
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