Mongodb 查询如何在 node.js 中工作？

Question

I have a very easy search query in Node.js Express.js MongoDB with Mongoose:

await Model.find({}).limit(10);

My question is how do the architects work? Is it first to get all Models Data and then limit to 10 or before getting all data will select 10 items from the database? I mean the steps:

1. Find all data from Model and return as List(Array) --> 2. Limit 10 first items and remove others from List(Array).

2. Find first 10 items and return as List(Array)

The difference in performance is high cause with first step if we got a million data it will return 1 mill items with a huge 10 20 sec and then limiting the 10 of it which we loose 10 20 seconds of time and when the user are more the server will be done but with the second way even with 100 mil items it will always take same time.

Answer 1

The limit function sets specifies the maximum number of elements a cursor will return. In the case of your example, the cursor will return the first 10 items matching the query only (option 2). You can find more information on how the cursor.limit() works via the links below:

• https://docs.mongodb.com/manual/reference/method/cursor.limit/
• http://mongodb.github.io/node-mongodb-native/3.5/api/Cursor.html#limit