C# 4 and .NET 4

Triggers ❘ 971
In this example, the associated table is Person.Contact, which is indicated by the Target property. The
Event property defines when the trigger should occur; here, the event string is set to FOR INSERT, which
means the trigger is started when a new row is inserted in the Users table.
The property SqlContext.TriggerContext returns the trigger context in an object of type
SqlTriggerContext. The SqlTriggerContext class offers three properties:
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ColumnsUpdated returns a Boolean array to flag every column that was changed
EventData contains the new and the original data of an update in XML format
TriggerAction returns an enumeration of type TriggerAction to mark the reason for the trigger
The following code compares whether the TriggerAction of the trigger context is set to TriggerAction.
Insert before continuing.
Triggers can access temporary tables; for example, in the following code listing the INSERTED table
is accessed. With INSERT, UPDATE, and DELETE SQL statements, temporary tables are created. The
INSERT statement creates an INSERTED table; the DELETE statement creates a DELETED table. With
the UPDATE statement both INSERTED and DELETED tables are used. The temporary tables have the same
columns as the table that is associated with the trigger. The SQL statement SELECT Username, Email
FROM INSERTED is used to access username and e-mail, and to check the e-mail address for correct syntax.
SqlCommand.ExecuteRow() returns a row represented in a SqlDataRecord. Username and e-mail are read
from the data record. Using the regular expression class, RegEx, the expression used with the IsMatch()
method checks if the e-mail address conforms to valid e-mail syntax. If it does not conform, an exception is
thrown and the record is not inserted, because a rollback occurs with the transaction:
using System;
using System.Data.SqlClient;
using System.Text.RegularExpressions;
using Microsoft.SqlServer.Server;
public partial class Triggers
{
[SqlTrigger(Name ="InsertContact", Target="Person.Contact",
Event="FOR INSERT")]
public static void InsertContact()
{
SqlTriggerContext triggerContext = SqlContext.TriggerContext;
if (triggerContext.TriggerAction == TriggerAction.Insert)
{
var connection = new SqlConnection("Context Connection=true");
var command = new SqlCommand();
command.Connection = connection;
command.CommandText = "SELECT EmailAddress FROM INSERTED";
connection.Open();
string email = (string)command.ExecuteScalar();
connection.Close();
}
}
}
if (!Regex.IsMatch(email,
@"([\w-]+\.)*[\w-]+@[\w-]+\.([\w-]+\.)*[\w]+$"))
{
throw new FormatException("Invalid email");
}
code snippet SqlSamplesUsingAdventureWorks/InsertContact.cs
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