[{"dataObj":{"dataObj_id":"test_1","cFS":{"data":[{"cf_id":"123","name":"cf_1"},{"cf_id":"456","name":"cf_2"}]}},"cfCoreData":[{"cf_id":"123","qf_id":"QF_1989"},{"cf_id":"456","qf_id":"QF_6090"}]}]

db.collection.aggregate([{$set:{"dataObj.cFS.data":{$map:{input:"$dataObj.cFS.data",as:"data",in:{$mergeObjects:["$$data",{$first:{$filter:{input:"$cfCoreData",cond:{$eq:["$$data.cf_id","$$this.cf_id"]}}}}]}}}}}])