How does Query.prototype.merge() works in Mongoose ?
The Query.prototype.merge() function is used to merge another Query or conditions object into the current query for which this function is used i.e this query. When a Query is passed, conditions, field selection and options are merged.
Syntax:
Query.prototype.merge()
Parameters: This function has one source parameter of Object/Query type.
Return Value: This function returns Query Object.
Mongoose Installation:
npm install mongoose
After installing the mongoose module, you can check your mongoose version in command prompt using the command.
npm mongoose --version
After that, you can just create a folder and add a file for example, index.js as shown below.
Database: The sample database used here is shown below:
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 } }); const query = User.find({age: { $gte:0 }}) console.log( "Before merge function" ) query.exec( function (err, res){ if (err) console.log(err) else console.log(res) }); setTimeout( function () { query.merge({name: "Gourav" }) console.log( "After merge function" ) query.exec( function (err, res){ if (err) console.log(err) else console.log(res) }); }, 1000); |
The project structure will look like this:
Run index.js file using below command:
node index.js
Output:
Before merge function
[
{ _id: 5ebb9129a99bde77b2efb809, name: ‘Gourav’, age: 10, __v: 0 },
{ _id: 5ebc3669a99bde77b2efb9ba, name: ‘Lalit’, age: 25, __v: 0 },
{ _id: 5ebc367da99bde77b2efb9bf, name: ‘Piyush’, age: 5, __v: 0 },
{ _id: 5ebd345f5d2d8a3534b2f391, name: ‘Manish’, age: 34, __v: 0 }
]
After merge function
[ { _id: 5ebb9129a99bde77b2efb809, name: ‘Gourav’, age: 10, __v: 0 } ]
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 } }); const query = User.find({age: { $gte: 1}}) console.log( "Before merge function" ) query.exec( function (err, res){ if (err) console.log(err) else console.log(res) }); setTimeout( function () { query.merge({name: "Gourav" }) console.log( "After merge function" ) query.exec( function (err, res){ if (err) console.log(err) else console.log(res) }); }, 1001); app.listen(3000, function (error ) { if (error) console.log(error) console.log( "Server listening on PORT 3000" ) }); |
The project structure will look like this:
Run index.js file using below command:
node index.js
Output:
Before merge function
Server listening on PORT 3000
[
{ _id: 5ebb9129a99bde77b2efb809, name: ‘Gourav’, age: 10, __v: 0 },
{ _id: 5ebc3669a99bde77b2efb9ba, name: ‘Lalit’, age: 25, __v: 0 },
{ _id: 5ebc367da99bde77b2efb9bf, name: ‘Piyush’, age: 5, __v: 0 },
{ _id: 5ebd345f5d2d8a3534b2f391, name: ‘Manish’, age: 34, __v: 0 }
]
After merge function
[ { _id: 5ebb9129a99bde77b2efb809, name: ‘Gourav’, age: 10, __v: 0 }
Reference: https://mongoosejs.com/docs/api/query.html#query_Query-merge