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I am creating a resolvers response mapping in AWS AppSync which is meant to perform a math calculation and return a percentage value as a float:

#set( $result = $ctx.source.total * 100 / 365000 )
$result

However VTL rounds this down each time to the nearest whole number such as 1.0, 2.0 etc.

Given 5000 * 100 / 365000:

Expected - 1.36 Result - 1.0

Is there anyway I can achieve this? or do I need to look towards using a Lambda (which feels overkill for something so simple).

leepowell
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2 Answers2

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The problem is that $ctx.source.total, 100, and 365000 are all treated as integers (java.lang.Integer) by VTL.

VTL does support floating point numbers via java.lang.Double. The VTL syntax for a double instead of an integer is just 100.0 instead of 100.

If any of the numbers in the assignment are doubles,$result will be a double.

So you could do this and get 1.36986301369863:

#set( $result = $ctx.source.total * 100.0 / 365000 )

Here's a link to some examples and example output:

https://mappingtool.dev/app/appsync/3d44255e560fa075b45bfa08afbb6fe4

Zac Charles
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In the case of the example above, the result would be 1.0 because 1.36 is rounded down to 1.0. To return the result as a float, you can use the Math.round() function and divide the result by 100:

#set( $result = Math.round($ctx.source.total * 100 / 365000) / 100 )
$result

This will return the result as a float with 2 decimal places.

To solve this problem, without using a Lambda and without using the Math.round() function, you can use the following VTL:

#set( $result = $ctx.source.total * 100 / 365000 )
#set( $result = $util.parseJson($util.toJson($result)) )
$result

This will return the result as a float with 2 decimal places.

Tibic4
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