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269 |
Writing Errors to the Event Log
Now that you understand how to capture each of the OleDB errors, let’s look at how you might log these errors to the System Event Log as well as display them to the user. Why would you want to write errors to the System Event Log? One reason is that whenever you are dealing with errors in the handling of data, you should provide multiple methods for identifying, troubleshooting, and resolving the issue. One method you can use to help identify certain errors is to write errors to the Event Log. This is especially useful in capturing issues that occur infrequently and may be difficult to track down.
In Listing 26-1 the last statement calls the WriteEvent() function. This function accepts as a parameter an exception and then goes through the process of writing the error summary to the Event Log. In order to use this function, you need to import the
System.Diagnostics namespace using:
<%@ Import Namespace=”System.Diagnostics”%>
Then you can implement the generic event log handler as shown in Listing 26-3 which completes Listing 26-2 discussed earlier in this session:
Listing 26-3 Writing error events to the system event log
Function WriteEvent(ByVal myException as Exception)
Dim sPage as String = Request.Path
Dim Message As String = “Url “ & sPage
Dim sLogName As String = “myLogFile”
Dim oLog as New EventLog
Message = Message & “ Error: “
Message = Message & myexception.message
If (Not EventLog.SourceExists(sLogName)) Then EventLog.CreateEventSource(sLogName,sLogName)
End if
oLog.Source = sLogName
oLog.WriteEntry(Message, EventLogEntryType.Error) End Function
</SCRIPT>
<BODY>
<FORM RUNAT=”server” ID=”Form1”> <H1>
ASP.NET OleDB Exception Handling </H1>
<P>
This example is useful for testing some of the typical errors that may
occur
while connecting to OleDB datasources. Try creating errors in the connection string and sql statements to see how error handling is
reported.
</P>
<P>
<ASP:LABEL RUNAT=”Server” ID=”Label1”>Connection String</ASP:LABEL>
Continued
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Sunday Morning |
Listing 26-3 |
Continued |
<ASP:TEXTBOX ID=”txtConnStr” RUNAT=”server” WRAP=”False” WIDTH=”800”>provider=sqloledb;Data Source=127.0.0.1;Initial Catalog=pubs;User ID=sa;pwd=;</ASP:TEXTBOX>
</P>
<P>
<ASP:LABEL RUNAT=”Server” ID=”Label2”>SQL Statement</ASP:LABEL> <ASP:TEXTBOX ID=”txtSQLStr” RUNAT=”server” WRAP=”False”
WIDTH=”800”>SELECT * FROM
GENERATE ERROR IN SQL</ASP:TEXTBOX> </P>
<P>
<ASP:BUTTON TEXT=”Execute Database Code” ONCLICK=”ExecuteDBCodeBtn_Click” RUNAT=”server” ID=”Button1” />
</P>
<P>
<ASP:DATAGRID ID=”grid1” RUNAT=”server” /> </P>
</FORM>
</BODY>
</HTML>
With this function, you are simply capturing the page that generated the error and, creating a new log file called myLogFile, or opening it if it already exists, then writing the message summary to the log file. That’s it! Now you can open the Event Viewer from your Control Panel Administrative Tools Event Viewer icon and review the log file, as illustrated in Figure 26-2, providing a way for remote administrators and local administrators to troubleshoot issues.
Figure 26-2 Using the Event Viewer to view errors in the Event Log
Session 26—Handling ADO.NET Errors |
271 |
REVIEW
You should now understand how to use the OLEDBException class and the OLEDBErrors collection to retrieve the errors that are produced by the OleDBDataAdapter. As the previous examples have shown, capturing these errors is straightforward — the real difficulty is resolving them!
QUIZ YOURSELF
1.How many OleDB errors can be handled by the OLEDBException class? (See “OLEDBError Object Description.”)
2.How could you implement a global generic OleDB error handler for use across your application? (See “OLEDBError Object Description.”)
3.If the first OleDB error in an OLEDBErrors collection contained the value Invalid column name ‘this’ in its Message property, then what would be the value of the OLEDBException.Message property wrapping this collection? (See “OLEDBError Object Properties.”)
P A R T
V
Sunday Morning
Part Review
The following set of questions is designed to provide you feedback on how well you understood the topics covered during this part of the book. Please refer to Appendix A for the answers to each question.
1.A DataSet object can be created without the use of the (SQL or ADO)
DataAdapter’s Fill method. True/False
2.The DataSet is a container class. True/False
3.Fill in the blank: The ______ property, which is read-only, returns the number of DataTables in a DataTableCollection object.
4.Fill in the blank: The ______ property gets a specified DataTable from a
DataTableCollection object.
5.Fill in the blank: ______ is the process of connecting a server control to a DataSet.
6.You can bind server controls to an array of custom classes. True/False
7.Setting the attribute AutoPostBack=”true” on a server control forces the reposting of the page to the server.
True/False
8.DTC objects are part of the ASP.NET Framework. True/False
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Part V–Sunday Morning Part Review |
9.Fill in the blank: The property ______ is what automatically generates the columns for a DataGrid control.
10.Using the following property/value combination, DataFormatString=”{0:C}” for a field will format the contents as what format type.
a.Decimal
b.Currency
c.Date
d.Fixed
11.To format alternating rows of data in a datagrid, manipulate which property?
a.HeaderStyle
b.FooterStyle
c.ItemStyle
d.AlternatingItemStyle
12.The DataReader control should be closed with the Close method. True/False
13.The U in CRUD stands for what?
a.Understand
b.Update
c.Unique
d.Undo
14.You must code your own modules to provide update, delete, and create functionality.
True/False
15.Fill in the blank: To set the number of records on each page, the ______
property should be set.
16.The RangeValidator Control cannot be used with the DataGrid when in Edit mode.
True/False
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275 |
17.Data shaping is simply the process of:
a.Reflecting the parent child relationships
b.Manipulating data values
c.Updating a DataSet
d.None of the above
18.A parent-child relationship is a type of hierarchy. True/False
19.The DataSet object can hold no more than 10 data tables. True/False
20.A special provider must be used to shape data with ADO.NET. True/False
21.Try...Catch...Finally is a type of structured error handling. True/False
22.The ADOException class acts as a ______ for the ADOErrors collection.
a.Wrapper
b.Object
c.Holding point
d.None of the above
23.What property provides a short description of the error that was generated?
a.Message
b.NativeError
c.Source
d.None of the above
24.What property retrieves the name of the object that generated the error?
a.Message
b.NativeError
c.Source
d.None of the above
P A R T
VI
Sunday
Afternoon
Session 27
SOAP It Up!
Session 28
Web Services
Session 29
Migrating from ASP to ASP.NET
Session 30
Migrating from ADO to ADO.NET