How to add a field to an existing JSON in Velocity? - json

Question

I have a JSON coming from a request body and I'm trying to use VTL to map it by adding an additional field to it. The request body looks like this:
{
"name": "John",
"age": 20,
"address": {
"street": "Albert's Street",
"City": "Test City"
}
}
In AWS, I'm trying to map this request body to have an additional field which is coming from a parameter in the URL path to become this:
{
"name": "John",
"age": 20,
"address": {
"street": "Albert's Street",
"City": "Test City"
},
"operation": "$input.params('path.operation')"
}
I have tried looping through with something like this but it doesn't work very well:
#set($allParams = $input.path('$'))
{
#foreach($type in $allParams.keySet())
#set($params = $allParams.get($type))
"$type" : {
#foreach($paramName in $params.keySet())
"$paramName" : "$util.escapeJavaScript($params.get($paramName))"
#if($foreach.hasNext),#end
#end
}
#if($foreach.hasNext),#end
#end
}
Moreover, this only works for those with 2 levels in the JSON. It doesn't work for those at the first level of the JSON or if I happen to have more than 2 levels in the JSON payload.
All I need is simply appending one more field into the existing request body of a JSON payload. How can I do that in Velocity?

Answer 1

You can add a operation property to the input JSON like this:
#set ($input.path('$').operation = 'example')
$input.json('$')
The above results in the following for your example:
{
"name": "John",
"age": 20,
"address": {
"street": "Albert's Street",
"City": "Test City"
},
"operation": "example"
}
Of course, you can use a value from params instead of 'example'.
By the way, consider running the param through $util.escapeJavaScript for added security.