How does Query.prototype.explain() work in Mongoose?
The Query.prototype.explain() function is used to set the explain option thereby making this query return detailed execution stats instead of the actual query result.
Syntax:
Query.prototype.explain()
Parameters: This function has one optional verbose parameter.
Return Value: This function returns Query Object.
Installing mongoose :
npm install mongoose
After installing the mongoose module, you can check your mongoose version in command prompt using the command.
npm mongoose --version
Now, create a folder and add a file for example, index.js as shown below.
Database: The sample database used here is shown below:
Project Structure: The project structure will look like this.
Example 1:
index.js
const mongoose = require( 'mongoose' ); // Database connection mongoose.connect( 'mongodb://127.0.0.1:27017/w3wiki' , { useNewUrlParser: true , useCreateIndex: true , useUnifiedTopology: true }); // User model const User = mongoose.model( 'User' , { name: { type: String }, age: { type: Number } }); var query = User.find({age: 5}).explain( 'queryPlanner' ) query.exec( function (err, res){ if (err) console.log(err.message) else console.log(res) }); |
Run index.js file using below command:
node index.js
Output :
[ { queryPlanner: { plannerVersion: 1, namespace: 'w3wiki.users', indexFilterSet: false, parsedQuery: [Object], queryHash: '3838C5A3', planCacheKey: '38305F3', winningPlan: [Object], rejectedPlans: [] }, executionStats: { executionSuccess: true, nReturned: 1, executionTimeMillis: 0, totalKeysExamined: 0, totalDocsExamined: 4, executionStages: [Object], allPlansExecution: [] }, serverInfo: { host: 'Lenovo530S', port: 27017, version: '4.2.0', gitVersion: 'a4b751dcf51dd249c58812b390cfd1c0129c30' }, ok: 1 } ]
Example 2:
index.js
const express = require( 'express' ); const mongoose = require( 'mongoose' ); const app = express() // Database connection mongoose.connect( 'mongodb://127.0.0.1:27017/w3wiki' , { useNewUrlParser: true , useCreateIndex: true , useUnifiedTopology: true }); // User model const User = mongoose.model( 'User' , { name: { type: String }, age: { type: Number } }); var query = User.find({age: 5}).explain( 'allPlansExecution' ) query.exec( function (err, res){ if (err) console.log(err.message) else console.log(res) }); app.listen(3000, function (error ) { if (error) console.log(error) console.log( "Server listening on PORT 3000" ) }); |
Run index.js file using below command:
node index.js
Output :
Server listening on PORT 3000 [ { queryPlanner: { plannerVersion: 1, namespace: 'w3wiki.users', indexFilterSet: false, parsedQuery: [Object], queryHash: '3838SF3', planCacheKey: '3238C5F3', winningPlan: [Object], rejectedPlans: [] }, executionStats: { executionSuccess: true, nReturned: 1, executionTimeMillis: 0, totalKeysExamined: 0, totalDocsExamined: 4, executionStages: [Object], allPlansExecution: [] }, serverInfo: { host: 'Lenovo530S', port: 27017, version: '4.2.0', gitVersion: 'a4b751dcf51sd249c5865812b390cfd1c0129c30' }, ok: 1 } ]
Reference:
https://mongoosejs.com/docs/api/query.html#query_Query-explain
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