Loops in CF: To loop or not to loop?

Loops in CF:To loop or not to loop? Neil Ross www.codesweeper.com neil@codesweeper.com

About Me • Developing Web Sites and Apps since ’95 • Worked for Allaire as CF Instructor and Consultant • Bayer, Lockheed, US Gov, State Govs • Articles in CFDJ, ‘Inside ColdFusion MX’ • Speaker at CF Dev Conf 2000, CFEurope 2003, CFUN03 • Freelance application design and development as Codesweeper • CFDJ Award Winner for PhotoFolio app (2nd Runner-Up) • Ask about my Not-Yet-Famous Application Framework

Introduction • Loops - many types • Many uses

Here is what we will be covering: For Loops While Loops Query Loops List Loops More advanced loops not covered: Structure Loops COM Loops Loop Types

What to use loops for • Use FOR loops when you know exactly how many times a set of statements should be executed • Use LIST loops when you want to loop over something other than numbers • Use WHILE loops when you want to execute a set of statements as long as a condition is True • Use QUERY loops when you want to repeat for all records in a query.

Loop uses • Repeating HTML • Processing text • Output queries • Nested Loops • Breaking out of loops • Banding report lines

FOR Loops • “FOR NEXT” loop <CFLOOP index="parameter_name“ from="beginning_value" to="ending_value"STEP="increment"> Lines to repeat </CFLOOP>

FOR CFLOOP Parameters • INDEX -name of variable that controls loop execution • FROM - starting loop value • TO - ending loop value • STEP – controls amount index variable is incremented (or decremented) in each loop iteration • Note: Loop may execute zero times if backwards - for example FROM 2 TO 1

<CFOUTPUT> <CFLOOP index="LoopCount" from="5" TO="1" step="-1"> The loop index is #LoopCount#.<BR> </CFLOOP> </CFOUTPUT> This produces…. FOR Loop Example 1 The loop index is 5. The loop index is 4. The loop index is 3. The loop index is 2. The loop index is 1.

FOR Loop Example 2 • HTML list boxes of hours that goes from 0 to 23 <SELECT NAME="Hour"> <CFOUTPUT> <CFLOOP INDEX="hour" FROM="0" TO="23"> <OPTION VALUE="#hour#">#hour# </CFLOOP> </CFOUTPUT> </SELECT>

Nested Loop Example • List box with all the hours and minutes of the day. <SELECT NAME="HourAndMinutes"> <CFOUTPUT> <CFLOOP INDEX="hour" FROM="0" TO="23"> <CFLOOP INDEX="minute" FROM="0" TO="59"> <OPTION VALUE="'#hour#:#minute#'">#hour#:#minute# </CFLOOP> </CFLOOP> <CFOUTPUT> </SELECT>

WHILE Loops • “DO WHILE” loop • Same syntax as CFIF conditional logic<CFSET Dice = 0><CFLOOP CONDITION="Dice LTE 5"> <CFSET Dice = RandRange(1,6)><CFOUTPUT>#dice#</CFOUTPUT><BR> </CFLOOP>

WHILE Loop Details • FOR and LIST loops are executed a certain number of times • WHILE loops are executed while a condition is true <CFLOOP CONDITION=“while-condition”> Statements to loop through </CFLOOP>

WHILE Loop Parameters • WHILE Loops • CONDITION contains a logical expression that is evaluated before each loop iteration • As long as CONDITION is true – the loop is executed • Tip - Make sure you change the values of variables used in CONDITION expression in the loop body – otherwise infinite loop!

Conditional operators • GT, LT, GTE, LTE, EQ, NEQ, IS, CONTAINS are the relational operators supported by ColdFusion • (don’t use > etc because CFML uses >) • AND, OR, NOT are the logical operators supported by ColdFusion • Use ()s to group expressions

Operator precedence • () • IS, EQ, NEQ, LT, LE, GT, GE • CONTAINS • NOT • AND • OR

CFBREAK • CFBREAK exits the current loop <CFSET StopIt = 0> <CFLOOP CONDITION=“TRUE”> <CFSET StopIt = RandRange(1,10)> <CFIF StopIt LTE 5> <CFBREAK> </CFIF> <CFOUTPUT>#StopIt#</CFOUTPUT><BR> </CFLOOP> More code here

Query Loops Query loops can be generated by three ColdFusion constructs. Those include the following: • CFOUTPUT • CFLOOP • CFMAIL

CFOUTPUT Query Loop <CFQUERY NAME="GetEmail" DATASOURCE="Library"> SELECT Email FROM Customer </CFQUERY> <CFOUTPUT QUERY="GetEmail"> #GetEmail.Email#<BR> </CFOUTPUT> • Variable available: • Queryname.currentrow • Queryname.recordcount

CFLOOP Query Loop <CFQUERY NAME="GetEmail" DATASOURCE="Library"> SELECT Email FROM Customer </CFQUERY> <CFOUTPUT> <CFLOOP QUERY="GetEmail"> #GetEmail.Email#<BR> </CFLOOP> </CFOUTPUT>

CFMAIL loop • Send one email for each record in the query <CFQUERY NAME="GetEmail" DATASOURCE="Library"> SELECT Email FROM Customer </CFQUERY> <CFMAIL QUERY="GetEmail" TO="#GetEmail.Email#" FROM="info@mycompany.com" SUBJECT=“Test” SERVER="smtp.mycompany.com"> Hi There </CFMAIL>

Nested Query Loop Example <CFQUERY NAME="GetEmail" DATASOURCE="Library"> SELECT Email , SecurityLevel FROM Customer </CFQUERY> <CFLOOP QUERY="GetEmail"> <CFQUERY NAME="GetText" DATASOURCE="Library"> SELECT EmailText, EmailSubject FROM Messages WHERE SecurityLevel = #GetEmail.SecurityLevel# </CFQUERY> <CFMAIL QUERY="GetText" TO="#GetEmail.Email#" FROM="info@mycompany.com" SUBJECT="#GetText.EmailSubject#" SERVER="smtp.mycompany.com">#GetText.EmailText# </CFMAIL> </CFLOOP>

Other record sets • You can loop over record sets from other tags than CFQUERY: • CFDIRECTORY – file list • CFPOP – read email • CFSEARCH – Verity text search • CFLDAP – LDAP records • CFWDDX

List Loops • “FOR EACH” loop <CFOUTPUT><CFLOOP INDEX="ListElement" LIST="#form.state#" DELIMITERS=","> #ListElement#<BR> </CFLOOP> </CFOUTPUT> • Other delimiters than comma are allowed

How list loops work • LIST loops allow you to list the values for the control variable instead of computing them as in the FOR loop <CFLOOP INDEX=“list_variable” LIST=“value_list”> Statements to loop through </CFLOOP>

List Loop parameters • INDEX - variable that controls loop execution • LIST - a list of comma separated values • INDEX is assigned the values in list one at a time as the loop executes • DELIMITERS – optional to give a delimiter other than comma

List Loop example • List local states <CFLOOP INDEX=“StateName” LIST=“MD, VA, DC”> <CFOUTPUT>#StateName# </CFOUTPUT><BR> </CFLOOP> Produces…. MD VA DC

Text file as a “list” • Text file processing by line can be done using lists • Read in text file using CFFILE • Use CR as delimiter • The list elements are now the lines in the file.

Read text file code • The following code reads a text file, then loops through the content of the file. <cffile action="READ" file="C:\afile.txt" variable="text_file"> <cfoutput> <CFLOOP list="#text_file#" index="line" delimiters="#CHR(13)#"> #line#<br> </CFLOOP> Count lines is #ListLen(text_file,"#CHR(13)#")# </CFOUTPUT>

CFSCRIPT Loops • CFScript is a JavaScript like language that provides the standard looping features of CFML plus a few more • For • While • Do-while • For-in

CFSCRIPT Loops syntax • FOR loop for (inital-expression; test-expression; final-expression) statement • WHILE loop while (expression) statement • UNTIL loop – evaluates condition in the loop do statement while (expression);

Resources • Macromedia LiveDocshttp://livedocs.macromedia.com/

Questions • Neil Ross www.codesweeper.comneil@codesweeper.com • Thanks to Sandy Clarkwww.shayna.com

Loops in CF: To loop or not to loop?