Using ADO in ASP in VS .NET

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Using ADO in ASP
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Active Server Page code has just a single data type called a variant This data type can act as any of the standard data types- but you can't initially assign it to a type When you coded a data type in Visual Basic or Access- you could do something like this: Dim I as Integer Dim TheMessage as String The first variable is implicitly declared as an Integer- and the second- as a String But in ASP- you would code this: Dim I Dim TheMessage Both variables have been declared as variants Each could be an integer or a string or even a complex object That means that they could even be an ADO object Therefore- in Visual Basic and in Access- you had this code: Dim MyConn as New ADODBConnection What you are saying with this line of code is that you want to create a variable called MyConn And the variable needs to be an instance of the Connection object of the ADODB library All the methods and properties of that object are now available to it So the next line of code could set one of the properties of the object: MyConnConnectionString = "driver={SQL Server};" _ & "server=MyServer;uid=SomeUser" _ & ";pwd=SomePassword;database=SomeDB" But- since ASP only has one data type- the variant- you would have this declaration: Dim MyConn The compiler knows nothing about the variable at this point It could be a String- a Long- or a Connection object The compiler will remain clueless until you assign a value or an object to that variant variable: Set MyConn = ServerCreateobject ("ADODBConnection") First- note the use of the Set statement This tells the compiler that you are assigning an object type to the MyConn variable You then use the method CreateObject of the intrinsic Server object to create an instance of the Connection object- which is an object of the ADO library The library type that you want to instantiate is passed to the CreateObject method through the parameter After this line of code- you can now assign values to the properties of the Connection object- like the connection string: MyConnConnectionString = "driver={SQL Server};" _ & "server=MyServer;uid=SomeUser" _ & ";pwd=SomePassword;database=SomeDB" and then call one of the methods of the Connection object to open the connection to the database: MyConnOpen This same procedure of using the CreateObject method to instantiate an object type can be used to instantiate many different libraries Here- the same procedure is used to create an e-mail object that is used to send out an e-mail message through ASP code: Dim objMail Set objMail = CreateObject("CDONTSNewMail") objMailSend "from@nacom"- "to@nacom"- _ "Subject Text"- "The text of the message" Set objMail = Nothing
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If Active Server Pages stood on their own without the interaction of a series of pages acting together as an application, they would not be very useful That is where Active Server Page applications come into play Active Server Page applications allow you to store information about the visitor's state and pass their information on from page to page For example, if you have a secure site, you need to pass on the identity of the visitor from page to page Without Active Server Page applications, you would need to ask the visitor to log in at each page they entered In this section, you will look at how to create and use the features of Active Server Page applications that are essential to using ASP as the front end to your SQL Server databases The first thing you need to do is establish that a series of Active Server Pages is an Active Server Page application An Active Server Page application is a series of Active Server Pages that are found in the same location either within the same file folder, or within subfolders of the parent directory of the application
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From your server computer, launch your Internet Services Manager and browse to the folder that contains the files that you want to make into an Active Server Page application Such a folder is displayed in Figure 15-1
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Figure 15-1: Internet Services Manager The files that you want to establish as being part of an application are in the folder called Chat Right-click the folder and select Properties You should then see a dialog box such as the one displayed in Figure 15-2
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Figure 15-2: Folder Properties without the folder as an application Notice the section labeled Application Settings This is where you tell the Internet Services Manager that this folder is an Active Server Page application Click the Create button The Application Name property should now be enabled, and you can enter a name for the application like the one displayed in Figure 15-3
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Figure 15-3: Folder Properties with the folder as an application Notice the drop-down menu labeled Execute Permissions; make sure that it is set to Scripts Only This setting allows the Active Server Pages in this folder to be run The property can also be set to None, which means that no code in this
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folder can be executed through a browser The third setting for this property is Scripts and Executables This allows code to run in your ASP pages, as well as in standard executable files Now take a look at the Application Protection drop-down This property is used to determine the isolation mode in which your code runs Setting the property determines whether problems with this application can affect other Active Server Page applications and the performance of the server The first option is Low If the property is set to this value, the application takes up fewer resources but the Active Server Page application can potentially take down IIS if the application fails The second setting is the default setting of Medium With this value, the application runs pooled with other ASP applications; so if your application fails, it could bring down other applications but shouldn't bring down IIS with it The third setting of High uses the most resources It isolates this Active Server Page application into its own process space Next, click the Configuration button to see the dialog box displayed in Figure 15-4
Figure 15-4: App Options tab of the Application Configuration dialog box The second tab in the Application Configuration dialog box is App Options Here, you set properties relating to the state of your Active Server Page application The first property is whether to Enable Session State If this property is selected, the pages within your ASP application can share information through the use of Session variables and Application variables A session in ASP lingo refers to requests made by an individual visitor as they travel from page to page in your site A session does not have knowledge or awareness of the state of other sessions, only its own Session variables allow you to pass data on from page to page, and save it between page calls until the visitor's session ends For example, say you have a Web site where you are allowing a student to answer a series of questions on a test You probably would want to store the ID of the student, the ID of the test, and the ID of the current question You would then want that information passed from page to page to maintain the visitor's state as they take the test You would have code like this: Session("StudentID") = 10 Session("TestID") = 42 Session("QuestionID") = 145 Since the variables are Session variables, any of the pages in the Active Server Page application can retrieve or set their value So, as you go from page to page in the test, you know what question to display, and on the results page of the test you can display the visitor's score Application variables are a little different Just like Session variables, they can be retrieved or set in any page of the Active Server Pages application But their scope goes beyond a single session They are available to any session within the Active Server Page application In the preceding example, you stored the ID of the student in a Session variable Another session could not access the value in this session It would have its own instance of the variable This is how you want it You don't want one session to know the ID of another student But sometimes you do need to pass information on between sessions You do this through Application variables Let's take the school example a bit further Say that you had many online schools on your server You managed them all, but each with its own content You could store all the test and course information in the same database and then access that data through separate ASP applications, each with its own school ID Each session would have to know the ID of the school that the session belonged to in order to display the correct content You could create an Application variable to store the ID of the school: Application("SchoolID") = 2
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Now, each session would know what school data to use So, checking the Enable Session State property on the App Options tab enables the use of these variables The next property on this page is the Session Timeout property A session ends when you call the Abandon method of the Session object: SessionAbandon or when the time between requests made by the visitors exceeds the number of minutes in the Session Timeout property If Enable Buffering is checked, all the code on your page runs before the results of the code are sent to the visitor's browser If Enable Parent Paths is checked, you can use relative positioning of a page in your code instead of specifying the full path to each page call The Default ASP Language is used to tell the compiler what language to use if you don't indicate a language name in your code The last property on this page is the ASP Script Timeout property This property represents the number of seconds you want to allow your code to run before it returns an error indicating that the code on the page did not complete This is helpful when your code is fresh and may contain endless loops Instead of running on until the whole application crashes, the script will just stop running if not complete by the number of seconds indicated in this property Now, select the App Debugging tab to see the dialog box displayed in Figure 15-5
Figure 15-5: App Debugging tab of the Application Configuration dialog box On this tab, you set debugging properties for your ASP application If the first box, Enable ASP Server-Side Script Debugging, is checked, when an error occurs on a page in this application, the Script Debugger will open on the server at the point of the error The second box, Enable ASP Client-Side Script Debugging, does nothing at this point Microsoft is reserving it for some possible future use The bottom section of the dialog box allows you to determine what the visitor sees when an error does occur If the first option is selected, the visitor will see the standard error message with the error number description and the erring line of code when an error occurs If the second option is selected, the visitor sees a text message that you enter into the provided text box Now close the dialog box and select the Documents tab from the Folder Properties dialog box as displayed in Figure 15-6
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