db={collection1:[{"_id":{"$oid":"6423cddbf4db0d397b22390a"},"dimension":[{"_id":{"$oid":"6423cde4f4db0d397b22390b"},"dimensionChild":"Wedding"},{"_id":{"$oid":"6423ce0af4db0d397b22390c"},"dimensionChild":"Business Casual"},{"_id":{"$oid":"6423ce18f4db0d397b22390d"},"dimensionChild":"Formal"}]}],collection2:[{"productTags":[{"$oid":"6423ce0af4db0d397b22390c"/** id from above doc*/},{"$oid":"6423b723f226c91a55d756bc"/** id from different document*/},{"$oid":"6423cde4f4db0d397b22390b"/** id from different document*/}]}]}

db.collection1.aggregate([{"$lookup":{"from":"collection2","localField":"productTags","foreignField":"dimension._id",as:"collection2"}},{$project:{dimension:{$filter:{input:"$dimension",cond:{$in:["$$this._id",{$getField:{input:{$first:"$collection2"},field:"productTags"}}]}}}}},{$unwind:"$dimension"},{$replaceRoot:{newRoot:"$dimension"}}])