Database
[{"_id":ObjectId("5f80a44d0179262f7c2e6a42"),"key":1},{"_id":ObjectId("5f8c00762fae890e9c4d029c"),"key":2},{"_id":ObjectId("5f802cf8abac1116a46bf9d4"),"key":3}]
Query
db.collection.aggregate([{$match:{_id:{$in:[ObjectId("5f8c00762fae890e9c4d029c"),ObjectId("5f802cf8abac1116a46bf9d4"),ObjectId("5f80a44d0179262f7c2e6a42")]}}},{$group:{_id:null,root:{$push:"$$ROOT"}}},{$addFields:{ids:[ObjectId("5f8c00762fae890e9c4d029c"),ObjectId("5f802cf8abac1116a46bf9d4"),ObjectId("5f80a44d0179262f7c2e6a42")]}},{$unwind:"$ids"},{$project:{root:{$reduce:{input:"$root",initialValue:{},in:{$cond:[{$eq:["$$this._id","$ids"]},"$$this","$$value"]}}}}},{$replaceWith:"$root"}])