[{"_id":1,"attr1":"x","class":"vehicle"},{"_id":2,"attr1":"xf","class":"vehicle"},{"_id":3,"attr1":"xz","class":"vehicle"},{"_id":4,"attr1":"xddz","class":"vehicle"},{"_id":11,"attr1":"xy","class":"seat","vehicle":[1,2]},{"_id":12,"attr1":"exy","class":"seat","vehicle":[3,2]}]

db.collection.aggregate([{"$group":{"_id":"$null","root":{"$push":"$$ROOT"},}},{$project:{_id:0,res:{"$filter":{"input":"$root","as":"values","cond":{$in:["$$values._id",{"$reduce":{input:"$root.vehicle",initialValue:[],in:{"$setUnion":["$$value","$$this"]},}},]}}}}},{"$unwind":"$res"},{"$replaceRoot":{"newRoot":"$res"}}])