Database
[{"_id":ObjectId("606b7046a0ccf72222c00c2f"),"groupId":ObjectId("5f06cca74e51ba15f5167b86"),"insertedAt":"2021-04-05T20:17:10.144521Z","isActive":true,"staffId":["606b6c34a0ccf72222c5a4df","606b6c48a0ccf722228aa035"],"subjectName":"Maths","teamId":ObjectId("6069a6a9a0ccf704e7f4b537"),"updatedAt":"2022-04-29T07:57:31.072067Z","syllabus":[{"chapterId":"626b9b94ae6cd2092024f3ee","chapterName":"chap1","topicsName":[{"topicId":"626b9b94ae6cd2092024f3ef","topicName":"1.1"},{"topicId":"626b9b94ae6cd2092024f3f0","topicName":"1.2"}]},{"chapterId":"626b9b94ae6cd2092024f3f1","chapterName":"chap2","topicsName":[{"topicId":"626b9b94ae6cd2092024f3f2","topicName":"2.1"},{"topicId":"626b9b94ae6cd2092024f3f3","topicName":"2.2"}]}]}]
Query
db.collection.aggregate([{$match:{"syllabus.topicsName.topicId":"626b9b94ae6cd2092024f3ef"}},{"$project":{result:{"$reduce":{"input":"$syllabus.topicsName","initialValue":[],"in":{"$concatArrays":["$$value","$$this"]}}}}},{"$project":{result:{"$filter":{"input":"$result","as":"r","cond":{$eq:["$$r.topicId","626b9b94ae6cd2092024f3ef"]}}}}}])