Unable to set array as environment variable - Postman test - postman

Question

I am trying to set an array as an environmental variable in postman.
But it stores the first value of the array rather than the array.
var aDataEntry = postman.pm.environment.get('data_set_entries');
if(aDataEntry == null) {
aDataEntry = [];
}
var jsonData = pm.response.json();
aDataEntry.push(jsonData.dataEntry.id);
// a console.log here confirms that aDataEntry is an array
postman.pm.environment.set('data_entry',aDataEntry);
As mentioned in the comment of the code, the variable is coming as an array,
but when I again get the environment variable in the second run, it is not
of type array. But just contains the first element in the array.
What's wrong here?
How can set the array and use it from the postman environment variable.

Answer 1

It seems like pm.environment.set calls toString to set an environment value. You can use the below code to work-around that:
var aDataEntry = pm.environment.get('data_set_entries');
if(aDataEntry == null) {
aDataEntry = [];
} else {
aDataEntry = JSON.parse(aDataEntry);
}
var jsonData = pm.response.json();
aDataEntry.push(jsonData.dataEntry.id);
// a console.log here confirms that aDataEntry is an array
pm.environment.set('data_entry',JSON.stringify(aDataEntry));
Edit 1:
As mentioned in the Postman reference docs, it is suggested that one use JSON.stringify() and JSON.parse() for storing complex objects. I have updated the code accordingly.

Answer 2

I'm not sure of how you intend to use the array, but to dynamically generate an array for use in a Body > raw > JSON POST, as in the answer above you do need to actually store the var as a string.
Here's an example of that and it's use in the POST Body. I had a long list of IDs, and I'm using Postman to do some bulk user profile updates.
In the Pre-request Script, generate the string to be POSTed as an array.
var externalIds = [111,222,333,444];
var attrString = "";
externalIds.forEach(userId => {
attrString += `,{"external_id": ${userId},"my_first_attribute": false,"my_next_attribute": true}`;
});
attrString = attrString.replace(',',''); // strip out that 1st unwanted comma
pm.environment.set("attributeArray",attrString);
The saved "array", Postman console logged:
"{"external_id": 111,"my_first_attribute": false,"my_next_attribute": true},
{"external_id": 222,"my_first_attribute": false,"my_next_attribute": true},
{"external_id": 333,"my_first_attribute": false,"my_next_attribute": true},
{"external_id": 444,"my_first_attribute": false,"my_next_attribute": true}"
Looks like bad, nested double quotes, but the format is actually valid.
My Body > raw looks like:
{
"api_key": "{{api_key}}",
"attributes": [{{attributeArray}}]
}
Note the Postman variable is wrapped in "[" and "]".
If my externalIds array needed to be a pm variable, I'd store that as a string, and .split() it when using it in the Script tab.
The Postman console really helps get past the syntax mistakes.