[{"_id":"12345679","module_id":"9898","module":{"module_details":{"data":[{"module_id":"9898","module_child_id":"2106123","value":"Username",},{"module_id":"9898","module_child_id":"2109909","value":"DOB",},{"module_id":"9898","module_child_id":"2110899","value":"Surname",}]},"module_child":{"data":[{"name":"Field Element 1","module_child_id":"2106123"},{"name":"Field Element 2","module_child_id":"2109909"},{"name":"Field Element 3","module_child_id":"2110899"}]}}}]

db.collection.aggregate([{"$unwind":"$module.module_details.data"},{"$unwind":"$module.module_child.data"},{$match:{$expr:{"$eq":["$module.module_child.data.module_child_id","$module.module_details.data.module_child_id"]}}},{$group:{"_id":"$_id",data:{$push:{"k":"$module.module_child.data.name","v":"$module.module_details.data.value"}}}},{"$project":{_id:1,child:{"$arrayToObject":"$data"}}}])