Loops in CF: To loop or not to loop?

1
Loops in CFTo loop or not to loop?

• Neil Ross
• www.codesweeper.com
• neil_at_codesweeper.com

2
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

3
Introduction

• Loops - many types
• Many uses

4
Loop Types

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

5
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.

6
Loop uses

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

7
FOR Loops

• FOR NEXT loop
• ltCFLOOP
• index"parameter_name from"beginning_value"
  
• to"ending_value"STEP"increment"gt
• Lines to repeat
• lt/CFLOOPgt

8
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

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FOR Loop Example 1

• ltCFOUTPUTgt ltCFLOOP index"LoopCount" from"5"
  TO"1" step"-1"gt
• The loop index is LoopCount.ltBRgt
• lt/CFLOOPgt
• lt/CFOUTPUTgt
• This produces.

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.
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FOR Loop Example 2

• HTML list boxes of hours that goes from 0 to 23
• ltSELECT NAME"Hour"gt
• ltCFOUTPUTgt
• ltCFLOOP INDEX"hour" FROM"0" TO"23"gt
•    ltOPTION VALUE"hour"gthour
• lt/CFLOOPgt
• lt/CFOUTPUTgt
• lt/SELECTgt

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Nested Loop Example

• List box with all the hours and minutes of the
  day.  
• ltSELECT NAME"HourAndMinutes"gt
• ltCFOUTPUTgt
• ltCFLOOP INDEX"hour" FROM"0" TO"23"gt
•   ltCFLOOP INDEX"minute" FROM"0" TO"59"gt
•         ltOPTION VALUE"'hourminute'"gthour
  minute
•   lt/CFLOOPgt
• lt/CFLOOPgt
• ltCFOUTPUTgt
• lt/SELECTgt

12
WHILE Loops

• DO WHILE loop
• Same syntax as CFIF conditional logicltCFSET
  Dice 0gtltCFLOOP CONDITION"Dice LTE 5"gt
  ltCFSET Dice RandRange(1,6)gtltCFOUTPUTgtdicelt/CF
  OUTPUTgtltBRgt
• lt/CFLOOPgt

13
WHILE Loop Details

• FOR and LIST loops are executed a certain number
  of times
• WHILE loops are executed while a condition is
  true
• ltCFLOOP CONDITIONwhile-conditiongt
• Statements to loop through
• lt/CFLOOPgt

14
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!

15
Conditional operators

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

16
Operator precedence

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

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CFBREAK

• CFBREAK exits the current loop
• ltCFSET StopIt 0gt
• ltCFLOOP CONDITIONTRUEgt
• ltCFSET StopIt RandRange(1,10)gt
• ltCFIF StopIt LTE 5gt
• ltCFBREAKgt
• lt/CFIFgt
• ltCFOUTPUTgtStopItlt/CFOUTPUTgtltBRgt
• lt/CFLOOPgt
• More code here

18
Query Loops

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

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CFOUTPUT Query Loop

• ltCFQUERY NAME"GetEmail"   DATASOURCE"Library"gt
•    SELECT Email FROM Customer
• lt/CFQUERYgt
• ltCFOUTPUT QUERY"GetEmail"gt
• GetEmail.EmailltBRgt
• lt/CFOUTPUTgt
• Variable available
• Queryname.currentrow
• Queryname.recordcount

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CFLOOP Query Loop

• ltCFQUERY NAME"GetEmail"   DATASOURCE"Library"gt
•    SELECT Email FROM Customer
• lt/CFQUERYgt
• ltCFOUTPUTgt
• ltCFLOOP QUERY"GetEmail"gt
• GetEmail.EmailltBRgt
• lt/CFLOOPgt
• lt/CFOUTPUTgt

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CFMAIL loop

•  Send one email for each record in the query 
• ltCFQUERY NAME"GetEmail"   DATASOURCE"Library"gt
•    SELECT Email FROM Customer
• lt/CFQUERYgt
• ltCFMAIL QUERY"GetEmail"
•       TO"GetEmail.Email"
•       FROM"info_at_mycompany.com"
•       SUBJECTTest
•       SERVER"smtp.mycompany.com"gt
• Hi There
•    lt/CFMAILgt

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Nested Query Loop Example

• ltCFQUERY NAME"GetEmail"   DATASOURCE"Library"gt
•    SELECT Email , SecurityLevel  FROM Customer
• lt/CFQUERYgt
• ltCFLOOP QUERY"GetEmail"gt
•    ltCFQUERY NAME"GetText" DATASOURCE"Library"gt
•       SELECT EmailText, EmailSubject FROM
  Messages
•       WHERE  SecurityLevel GetEmail.SecurityLev
  el
•    lt/CFQUERYgt
•     ltCFMAIL QUERY"GetText"
•       TO"GetEmail.Email"
•       FROM"info_at_mycompany.com"
•       SUBJECT"GetText.EmailSubject"
•       SERVER"smtp.mycompany.com"gtGetText.EmailTe
  xt
•    lt/CFMAILgt
• lt/CFLOOPgt

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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

24
List Loops

• FOR EACH loop
• ltCFOUTPUTgtltCFLOOP INDEX"ListElement"
• LIST"form.state"
• DELIMITERS","gt
• ListElementltBRgt
• lt/CFLOOPgt
• lt/CFOUTPUTgt
• Other delimiters than comma are allowed

25
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
• ltCFLOOP INDEXlist_variable
  LISTvalue_listgt
• Statements to loop through
• lt/CFLOOPgt

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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

27
List Loop example

• List local states
• ltCFLOOP INDEXStateName
• LISTMD, VA, DCgt
• ltCFOUTPUTgtStateName
• lt/CFOUTPUTgtltBRgt
• lt/CFLOOPgt
• Produces.

MD VA DC
28
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.

29
Read text file code

• The following code reads a text file, then loops
  through the content of the file.
• ltcffile action"READ" file"C\afile.txt"
  variable"text_file"gt
• ltcfoutputgt
• ltCFLOOP list"text_file" index"line"
  delimiters"CHR(13)"gt
• lineltbrgt
• lt/CFLOOPgt
• Count lines is
• ListLen(text_file,"CHR(13)")
• lt/CFOUTPUTgt

30
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

31
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)

32
Resources

• Macromedia LiveDocshttp//livedocs.macromedia.com
  /

33
Questions

• Neil Ross www.codesweeper.comneil_at_codesweeper.co
  m
• Thanks to Sandy Clarkwww.shayna.com