Velocity: Is a any way to check if variable is defined

Question

I want to include one template nested into others cont1, cont2, cont3. And nested template should be hide one specific control for cont1 only. Before inclusion into cont1 I would like to assign value to some flag variable $hideMyControl.

And inside nested template I would like to check if $hideMyControl is assigned value.

How to perform such check?

score 37 · Answer 1 · edited Oct 11 '22 at 12:58

37

#if($hideMyControl)
    // your code
#end

If $hideMyControl is defined, your code will execute

edited Oct 11 '22 at 12:58

Yves M.

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answered Feb 14 '13 at 00:49

onlinehood

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score 23 · Accepted Answer · edited Feb 05 '13 at 16:45

23

You can do this using

  #if($!{$articleLeader})
      // Perform your operation or the template part you want to show.
  #end

For more info, see the 'formal reference' section of the Apache Velocity Reference Manual.

edited Feb 05 '13 at 16:45

StackExchange What The Heck

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answered Jan 28 '11 at 08:54

sagar27

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There's no point to using formal and silent notation in an #if, which you didn't quite get right anyway. Just do #if( $article ) ## perform op here #end – Nathan Bubna Jan 28 '11 at 18:13
2

So what about checking if it's NOT defined? – Snekse Jun 21 '13 at 18:30
This answer users [Quiet Reference Notation](http://velocity.apache.org/engine/2.0/user-guide.html#quiet-reference-notation) that may lead to exception being thrown on undefined reference in [Strict Reference Mode](http://velocity.apache.org/engine/2.0/user-guide.html#strict-reference-mode). See [VELOCITY-739](https://issues.apache.org/jira/browse/VELOCITY-739). – Vadzim Feb 15 '19 at 12:16

score 11 · Answer 3 · answered Jan 17 '17 at 13:39

11

#if($!{hideMyControl} != "")
## do something if $hideMyControl is defined
#end

This works for me in AWS API Gateway Body Mapping Templates. Please refer to Quiet Reference Notation in Velocity User Guide for more information.

answered Jan 17 '17 at 13:39

erabbit

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Only one that worked for me in AWS API Gateway Body Mapping Templates. – leo Jan 23 '17 at 14:50

score 1 · Answer 4 · answered Apr 04 '17 at 17:03

1

I was using

#if ($hideMyControl) 
    //do something 
#end

since a few months ago, however today its not working anymore.

I came here to find help, and noticed a new way of writing it :

#if($!{$hideMyControl})
   // do something
#end

this code works!

answered Apr 04 '17 at 17:03

Max Alexander Hanna

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`since a few months ago, however today its not working anymore.` Is this maybe a Velocity 2.0 migration issue? - see "method arguments are now converted as needed between all main basic Java standard types (booleans, numbers and strings)." – Patrick Feb 19 '19 at 12:43
wow im glad i left the job that hired me to do that a few years ago, no one ever told me they migrated versions as i was coding up the EDI part of their ERP systems using that language. glad i left that company it was a shitshow lol. – Max Alexander Hanna Feb 19 '19 at 15:10

score 1 · Answer 5 · answered Jun 21 '17 at 16:07

According to the docs for Strict Reference Mode it is possible to several constructions to check if variable is defined.

#if ($foo)#end                  ## False
#if ( ! $foo)#end               ## True
#if ($foo && $foo.bar)#end      ## False and $foo.bar will not be evaluated
#if ($foo && $foo == "bar")#end ## False and $foo == "bar" wil not be evaluated
#if ($foo1 || $foo2)#end        ## False $foo1 and $foo2 are not defined

So this code works in my case.

#if( !$value )
  // Perform your operation or the template part you want to show.
#end

user07 · Answer 6 · 2016-02-25T05:32:38.163

0

To check if $hideMyControl is in Velocity context and IS NOT boolean 'true' value (or 'false' as well):

#if ($hideMyControl && $hideMyControl != true)
    ##do stuff
#end

Sure, if you really use your $hideMyControl variable as boolean type, you don't need second part of condition.

edited Feb 25 '16 at 05:32

answered Feb 25 '16 at 05:20

user07

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Velocity: Is a any way to check if variable is defined

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