Velocitip: A syntax slip might not throw a fatal error, but can be a big deal

SanfordWhiteman · ‎03-23-2024

Take this VTL snippet, intended to output trial keys for known combos of Country and custom field Intended Use:

#if( $lead.Intended_Use__c.equals("MycoAlert Trial Kit")) && ($lead.Country.equals("United States") )
KGFV-WJN7-CW43
#elseif( $lead.Intended_Use__c.equals("MycoAlert Plus Trial Kit")) && ($lead.Country.equals("United States") )
7XFC-WFZP-CTDY
#elseif( $lead.Intended_Use__c.equals("MycoAlert Trial Kit")) && ($lead.Country.equals("Austria") )
VTQF-RL0D-Q6NJ
#elseif( $lead.Intended_Use__c.equals("MycoAlert Plus Trial Kit")) && ($lead.Country.equals("Austria") )
QZIC-L36N-2BDQ
#end

At a glance, what do you think the output will be for this lead:

Now click below to reveal the actual output:

Spoiler

&& (false )
KGFV-WJN7-CW43

Not what you expected?

Perhaps you counted the right and left parentheses, and indeed there are four opening ( and four closing ) on each line. But you missed that:

the && “operator” isn’t an operator here: it’s outside of the #elseif() directive, so it’s just just two ampersand characters with no special meaning
$lead.Country.equals("United States") is also outside the #elseif(), so it’s treated as standalone output

See, Velocity — like all template languages — centers on output. So anything between #-directives or $-references, as long as it doesn’t otherwise violate VTL grammar, is assumed to be a literal string.

You couldn’t get away with that wandering && in non-template languages. In JS, for example, this is a fatal syntax error:

if( lead.someProperty === "Some Value" ) { &&
}

Making it work

Here’s the code you probably thought you were seeing above:

#if( $lead.Intended_Use__c.equals("MycoAlert Trial Kit") && $lead.Country.equals("United States") )
KGFV-WJN7-CW43
#elseif( $lead.Intended_Use__c.equals("MycoAlert Plus Trial Kit") && $lead.Country.equals("United States") )
7XFC-WFZP-CTDY
#elseif( $lead.Intended_Use__c.equals("MycoAlert Trial Kit") && $lead.Country.equals("Austria") )
VTQF-RL0D-Q6NJ
#elseif( $lead.Intended_Use__c.equals("MycoAlert Plus Trial Kit") && $lead.Country.equals("Austria") )
QZIC-L36N-2BDQ
#end

Now, the && is an actual operator and $lead.Country is part of the condition.

**Making it shorter and better**

The fixed code above will work, but it’s hard to maintain as string constants are peppered throughout the code.

Better to use a map-first approach where you put all the strings up top, leaving you with only one line of “code” proper!

#set( $trialKeyPatterns = {
  ["MycoAlert Trial Kit","United States"] : "KGFV-WJN7-CW43",
  ["MycoAlert Plus Trial Kit","United States"] : "7XFC-WFZP-CTDY",
  ["MycoAlert Trial Kit","Austria"] : "VTQF-RL0D-Q6NJ",
  ["MycoAlert Plus Trial Kit","Austria"] : "QZIC-L36N-2BDQ"
})
${trialKeyPatterns.get([$lead.Intended_Use__c, $lead.Country])}

This works because the keys of a Java LinkedHashMap use value equivalence (equals), rather than reference equality (==).✱ So map.get(key) finds the item whose key equals(key). Here, key is an ArrayList, and ArrayList.equals means “Are all indexes and items equal?”

In other words:

#set( $listA = ["MycoAlert Trial Kit","United States"] )
#set( $listB = ["MycoAlert Trial Kit","United States"] )
#set( $areTheyEqual = $listA.equals($listB) ) ## true
#set( $listC = ["United States","MycoAlert Trial Kit"] )
#set( $areTheyEqual = $listA.equals($listC) ) ## false
#set( $mapD = {
  $listA : "hello"
} )
#set( $getKey = $mapD.get($listA) ) ## "hello"
#set( $getKey = $mapD.get($listB) ) ## "hello"
#set( $getKey = $mapD.get($listC) ) ## null

NOTES

✱ Yes, the terms are kind of confusing, even more so when you consider that Velocity ==, which we’re constantly reminding people not to use because it can act weird, isn’t the same as Java ==.

SaurabhGoyal_GN · ‎03-26-2024

Nice learning about velocity scripting. Thanks for the guidance as always @SanfordWhiteman .