A simple question, let's have this query : user_result = db.users.find({"_id": "anyID"})

Is it more performant than user_result = db.users.find({"_id": "anyID"}).limit(1) if i know that this query should return only one result.

CodePudding user response：

If you compare the results if .explain() you will find that the winning plan in both cases is IDHACK. .limit(1) will not provide any perf gains.

db.users.find({"_id": "anyID"}).limit(1).explain()
db.users.find({"_id": "anyID"}).explain()

Similar question on MongoDB WinningPlan IDHACK

Also, you probably want to do a findOne() in this case.

db.users.findOne({"_id": "anyID"})

Keep in mind that the return value of findOne() differs from that of find(). FindOne returns the document, whereas Find returns a cursor.