Database
[{_id:ObjectId("649d0bae47fa0b4db69f2cf6")},{_id:ObjectId("649d0bae47fa0b4db69f2cf8")},{_id:ObjectId("649d0bae47fa0b4db69f2cf9")}]
Query
db.collection.update({$expr:{$in:[{$toString:"$_id"},["649d0bae47fa0b4db69f2cf6","649d0bae47fa0b4db69f2cf8"]]}},[{$set:{someField:{$first:{$reduce:{input:{$objectToArray:{"649d0bae47fa0b4db69f2cf6":1,"649d0bae47fa0b4db69f2cf8":2}},initialValue:[],in:{$concatArrays:["$$value",{$cond:[{$eq:["$$this.k",{$toString:"$_id"}]},["$$this.v"],[]]}]}}}}}}],{multi:true})