Database
[{"docId":"x1"},{"docId":"x2"},{"docId":"x3"},{"docId":"x4"},{"docId":"x5"},{"docId":"x434"},{"docId":"x6"},]
Query
db.collection.aggregate([{$facet:{all:[{$match:{docId:{$ne:"x434"}}},{$limit:2}],wanted:[{$match:{docId:"x434"}}]}},{$project:{data:{$concatArrays:["$wanted","$all"]}}},{$unwind:"$data"},{$replaceRoot:{newRoot:"$data"}}])