tips, trick and techniques for asp developers atlanta asp user group don draper draper consulting,...

Tips, Trick and Techniquesfor ASP Developers

Atlanta ASP User Group

Don DraperDraper Consulting, Inc.

Don@draperconsulting.com

http://www.draperconsulting.com

February 10, 2000 Draper Consulting, Inc. http://www.draperconsulting.com

Topics

• Transact-SQL Techniques

• Handling Expired Session Techniques

• Background Images in Tables

• JavaScript Tips

• The Response Object

• Understanding HTTP Headers

Transact-SQL Techniques

Transact-SQL, Technique #1Ad-Hoc WHERE Clause

• Problem: User can enter any selection criteria in multiple fields for ad-hoc query, but data source is a stored procedure.

• Solution: WHERE (col1 = @arg1 OR @arg1 is null) AND (col2 like @arg2 OR @arg2 is null) AND (col3 like @arg3 OR @arg3 is null)

• In ASP Code…– Make sure empty parameters are passed as

nulls if parm = empty then parm = null

– Can use Parameter ObjectSet param1 = cmd.CreateParameter ("city", adVarChar,adParamInput,15,city)

Set param2 = cmd.CreateParameter ("company", adVarChar, adParamInput, 40, company)

cmd.Parameters.Append param1

• In ASP Code…– Can use Array function to pass params

city = request("city")

if city = empty then city = Null ‘ pass null to sp if not needed

Set rs = cmd.Execute (recs, Array( company, city ) )

• In Stored Procedure…– default arguments to null

@companyname varchar(40) = null, …

– use “Is null”..NOT “= null”Good: WHERE (company like @company OR @company is

Bad: WHERE (company like @company OR @company = null)

Transact-SQL, Technique #2Ad-Hoc ORDER BY Clause

• Problem: User can click on any header in table and the result set is reordered for that column. However, the data source is a stored procedure. How can I alter ORDER BY clause?

Solution #1: Use Exec() – lose precompiled advantage of stored proce

• Solution #2: Use ANSI CASE (better)– Retain precompiled advantage of stored proc

Transact-SQL, Technique #2Ad-Hoc ORDER BY Clause

• Sample Code for Stored Procedure

ORDER BY

CASE @sort passed in a argument to procedure

WHEN 'id' THEN CAST (CustomerID as varchar(20))

WHEN 'companyname' THEN companyname

WHEN 'city' THEN city

ELSE CAST (CustomerID as varchar(20))

Handling Expired Sessions

• We use sessions to …– Maintain state information– Maintain user specific data across pages– Provide additional security…and more

• Sessions end by – Session.Abandon– Session expires due to period of inactivity

• When session expires– Need user to start over

• login again• start new session & re-establish session data

• Techniques to check for current session– Check for session value at top of page– Let session events handle it for you!

• Typical Technique:– Check for session variable at the top of

each page

If session(“userid”) = “” then

redirect(“login.asp”)

End if

• Suggested Technique:– Let a session event handle it for you– In Global.ASA file Session_OnStart

• Check referring URL• Redirect/Transfer if not coming from your start (login?)

fromURL = Request.ServerVariables("URL")

if InStr(lcase(fromURL), "login.asp") = 0 then

Response.Redirect("expired_page.asp")

end if

• Watch out for…– login page is ASP page

• Session already started before login – Use <@ EnableSessionState = FALSE>– Use Session.Abandon to kill session

– other pages that start session before login• Same as above

– use NT Performance Monitor to watch session count when testing

Background Images in Tables

Table background images offer an easy way to place other elements over an image. Cell can be used for positioning.

• Problem: Background images can be defined as

an attribute of a TABLE tag. This permits elements such as text, fields and more to be place over an image.

However, Netscape renders the image starting in each cell, even if defined at the TABLE level!

</TABLE>

Netscape renders the image inside each cell, even if defined at the TABLE level. As you can see, this is not acceptable!

• Solution: Use two nested tables– Outer table

• gets one empty cell to hold inner table• background attribute defined in Table tag

– Inner table• background attribute in Table tag but with

empty value ( background=“” )

• Use cells to position elements over image

Client-Side JavaScript

• Two common uses…– Place cursor in appropriate form field– Client-side form validation

• Place cursor in appropriate form fielddocument.formname.fieldname.focus();

Client-Side JavaScriptPlace cursor in UID field if empty…otherwise place in

password field

document.forms[0].as_password.focus();else

document.forms[0].as_userid.focus();}// --></script>

Use // to comment out closing HTML comments <script language="JavaScript">

function myfunction( ) {

// --> the js comment (//) prevents errors in some browsers

</script>

FormChek.js - Form Validation Library • Free, Public Domain Library• Over 60K of validation routines by Eric Krock, NS

– Basic data validation routines– Reformat data– Prompt user– Interactively check field contents– Credit card validation

Understanding HTTP Headers

Understanding HTTP Headers?

• Request Headers (from browser)– GET - hyperlink request– POST - FORM request (default)

• Response Headers (from server or ASP code)– Content-Type: - defines type of content– Location: - redirect browsers to URL– Set-Cookie: - stores data on browser

Pages / ASP

FunctionA( )FunctionB( )FunctionC(a)..

Pages / ASP

FunctionA( )FunctionB( )FunctionC(a)..

Request & Response

IIS / ASP(server)Web browser

HTTP Request

HTTP Response

GET URL HTTP/1.0

HTML page or binary content (PDF) prefixed with HTTP Response Headers

HTTP Response Headers

My Web Page!

</BODY></HTML>

My Web Page!

</BODY></HTML>

HTTP/1.0 200 OKServer: Apache/1.1.1Content-Type: text/htmlContent-Length: 31078

HTML Page

HTTP Headers

HTTP Header Format

• Each header is on its own line with no blank lines between them

• The last header is followed by a blank line and then the content

HTTP Headers

My Web Page!

</BODY></HTML></BODY>

My Web Page!

</BODY></HTML></BODY>

HTTP/1.0 200 OKServer: Apache/1.1.1Content-Type: text/htmlContent-Length: text/html

HTML Page

Headers added by Web Server

Headers you can control

One blank line separates

headers from

content

Common HTTP Response Headers

• Location: (redirection)

• Content-Type: (MIME type of content)

• Content-Length: (length of content)

• Set-Cookie: (save data on browser)

The Response Object

• Collections– Cookies

• Properties– Buffer– CacheControl– CharSet– ContentType– Expires– ExpiresAbsolute– IsClientConnected– Status

• Methods– AddHeader– AppendToLog– BinaryWrite– Clear– End– Flush– PICS– Redirect– Write

The Response Object

• Collections–

• Properties– Buffer– – – – – – –

• Methods– AddHeader– – – Clear– End– Flush– – Redirect–

Tips for Using Flush and End

• Response.Flush– Flush after page titles but before long database

queries to increase perception of speed– Output continue to fill buffer after Flush is used– Response.Buffer must be TRUE

• Response.End– Stops further output to the browser– Use Clear to remove output prior to End

Tips for Using Clear and Redirect

• Response.Clear– Clear page content since the last Flush or Clear;

headers are still sent– Useful to display only error message instead of

standard page content

• Response.Redirect– Sends 302 Object Moved response error– Buffer must be true if content already sent– Don’t need Clear prior to Redirect

Redirect(“file2.asp”)Redirect(“file2.asp”)

Request & ResponseRedirect Requires 2 Round Trips to Server

IIS / ASP(server)Web browser

Request: GET /file1.asp HTTP/1.0

Response: 302 Object MovedLocation: file2.asp

File1.asp

File2.asp

Response: 200 OkHTTP/1.1 200 OK

Server: Microsoft-IIS/4.0Date: Wed, 16 Feb 2000 10:26:53 GMT

Content-Length: 218Content-Type: text/html

Server.Transfer(“File2.ASP”)

Request & ResponseServer.Transfer Requires Only 1 Trip to Server

(ASP 3.0)

IIS / ASP 3.0(server)Web browser

File1.asp

File2.asp

Response: 200 OkHTTP/1.1 200 OK

Server: Microsoft-IIS/4.0Date: Wed, 16 Feb 2000 10:26:53 GMT

Content-Length: 218Content-Type: text/html

Server send back different file

More Information

• Ostrosoft Internet Tools– http://www.ostrosoft.com

• HTTP Protocol and Headers– http://www.w3.org/Protocols/rfc2616/rfc2616.html

• FormChek.js– Look in search engines– http://www.draperconsulting.com/downloads/formchek.zip

More Information

• Wrox Books– Professional Active Server Pages 2.0 (3.0)– ASP 2.0 (2.1) Programmers Reference– ADO 2.0 (2.5) Programmers Reference– http://www.wrox.com– http://webdev.wrox.co.uk/books/BookList.asp

Questions?

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