How to omit null values in JSON AssignMessage payload in APIGEE? - apigee

Question

I built a proxy that basically expects a different JSON input object than the one the final endpoint is expecting to receive. So, in order to bridge the request object from one to the other I'm using an AssingMessage policy to transform the json input.
I'm doing something like this:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<AssignMessage async="false" continueOnError="false" enabled="true" name="Assign-Message-Sample">
<DisplayName>Assign Message-Sample</DisplayName>
<Remove>
<Headers>
<Header name="login_id"/>
<Header name="Authorization"/>
</Headers>
<Payload>true</Payload>
</Remove>
<Set>
<Payload contentType="application/json">
{
"valueA": "{clientrequest.valueA}",
"valueB": "{clientrequest.valueB}",
"valueC": "{clientrequest.valueC}",
"valueD": "{clientrequest.valueD}",
"valueE": "{clientrequest.valueE}",
"valueF": "{clientrequest.valueF}",
}
</Payload>
<Verb>POST</Verb>
</Set>
<IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
<AssignTo createNew="false" transport="http" type="request"/>
</AssignMessage>
The problem comes when some of the values are empty. The destination server does not handle properly any empty values (escapes from my control).
My question is: how can I skip entirely a parameter if value is empty?
I'm looking for something like this (or better alternative):
<Payload contentType="application/json">
{
<skip-if-empty name="clientrequest.valueA">
"valueA": "{clientrequest.valueA}",
</skip-if-empty>
"valueB": "{clientrequest.valueB}",
...
}
</Payload>

Answer 1

For what I have found from my research, it seems this is a job for a Javascript Policy.
How is this done?
You basically need to place a javascript policy right before the AssignMessage execution. In the javascript policy you have the freedom to apply all the logic to omit certain parameters if values are not provided.
So for example, say we have already extracted the request values to variables using an ExtractVariables policy. Then, in the Javascript policy we can validate those values and build the resulting JSON object to later store it in another variable that will be picked up by the AssingMessage policy.
javascript policy:
var valueA = context.getVariable("clientrequest.valueA"),
valueB = context.getVariable("clientrequest.valueB"),
valueC = context.getVariable("clientrequest.valueC"),
...
var result = {};
if(valueB) {
result.b = valueB;
}
if(valueA) {
result.a = valueA;
}
if(valueC) {
result.c = valueC;
}
...
context.setVariable("newInput", JSON.stringify(result));
Then our AssignMessage will just pick up the variable we just stored: "newInput" that will contain the complete JSON object string:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<AssignMessage async="false" continueOnError="false" enabled="true" name="Assign-Message-Sample">
<DisplayName>Assign Message-Sample</DisplayName>
<Remove>
<Headers>
<Header name="login_id"/>
<Header name="Authorization"/>
</Headers>
<Payload>true</Payload>
</Remove>
<Set>
<Payload contentType="application/json">
{newInput}
</Payload>
<Verb>POST</Verb>
</Set>
<IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
<AssignTo createNew="false" transport="http" type="request"/>
</AssignMessage>
This solution worked fine for me. I hope someone else finds it helpful.