How to pass variables many level down in mongodb aggregation

Working with Data
, ,
1

I want to pass the report id variable into the pipeline stage of the user’s collection to filter the (clear) field array to get only objects owned by this report

const reports = await Report.aggregate([
      {
        $lookup: {
          from: 'operations',
          let: { operationId: '$operation', reportId: '$_id' /* I don't know if this is right or if there's a better way to get the report id */ },
          pipeline: [
            {
              $match: { $expr: { $eq: ['$_id', '$$operationId'] } },
            },
            {
              $lookup: {
                from: 'users',
                let: {
                  userId: '$initiator.user', type: '$initiator.type'},
                pipeline: [
                  { $match: { $expr: { $eq: ['$_id', '$$userId'] } } },
                  {
                    $project: {
                      color: '$colorCode.code',
                      avatar: 1,
                      type: '$$type',
                      clear: {
                        $filter: {
                          input: '$clear',
                          as: 'clear',
                          cond: {
                            $eq: [
                              '$clear.report',
                              '6375856e1f7e265016ffd3c8', /* here i want to pass the reporId */
                            ],
                          },
                        },
                      },
                    },
                  },
                ],
                as: 'initiator',
              },
            },
            {
              $lookup: {
                from: 'users',
                let: {
                  userId: '$peer.user', type: '$peer.type',
                },
                pipeline: [
                  { $match: { $expr: { $eq: ['$_id', '$$userId'] } } },
                  {
                    $project: {
                      color: '$colorCode.code',
                      avatar: 1,
                      type: '$$type',
                      clear: {
                        $filter: {
                          input: '$clear',
                          as: 'clear',
                          cond: {
                            $eq: [
                              '$clear.report',
                              '6375856e1f7e265016ffd3c8', /* same here */
                            ],
                          },
                        },
                      },
                    },
                  },
                ],
                as: 'peer',
              },
            },
            {
              $unwind: '$initiator',
            },
            {
              $unwind: '$peer',
            },
          ],

          as: 'operation',
        },
      },
      {
        $unwind: '$operation',
      },
])
2

I am not sure I understand correctly but you could use $addFields just before the inner $lookup. This way it is available an any other field.