Pipeline: accessing variables defined in $let

Working with Data
1

Hello!

Is there a way to output the actual values of the variables defined in the “$let” stage of a lookup? For debug purposes, I mean.

In something like
$lookup{…
let: {source: “SOURCE”, joinKey: “$CONC_DN”, dataType: “EVALS”, endDate: {$add: [{$toDate:"$SCHEDULEDDATE"}, -(31000606024)]}},
…

I would like to see whether endDate is actually correct (3 days before the value of SCHEDULEDDATE)

Thank you in advance!

2

Here is an example of how you can debug your custom vars inside $lookup.pipeline:

const pipeline = [
  {
    $lookup: {
      from: 'other_collection',
      let: {
        varA: '$parentProp',
      },
      pipeline: [
        {
          // this is needed to output only 1 doc with vars
          // and hide all the unnecessary fields
          $group: {
            _id: null,
          },
        },
        {
          $addFields: {
            debugVarA: '$$varA',
          },
        },
      ],
      as: 'result',
    },
  },
];