Mongoose Query() Function

The Query constructor is used for building the queries. So the user does not need to instantiate a Query directly. The `query` is an instance of `Query`.

Syntax:

Query()

Parameters: This function has optional parameters like model, condition, collection and options.

Return Value: This function returns Query object.

Installation of mongoose module:

• You can visit the link to Install mongoose module. You can install this package by using this command. 

npm install mongoose

• After installing the mongoose module, you can check your mongoose version in command prompt using the command. 

npm version mongoose

• After that, you can just create a folder and add a file for example, index.js as shown below.

Example 1: Filename: index.js

javascript

const express = require('express');
const mongoose = require('mongoose');
const app = express()

// Database connection
mongoose.connect('mongodb://127.0.0.1:27017/geeksforgeeks', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

// User model
const User = mongoose.model('User', {
    name: { type: String },
    age: { type: Number }
});

const query = new mongoose.Query();
console.log(query);

app.listen(3000, function(error ){
    if(error) console.log(error)
    console.log("Server listening on PORT 3000")
})

Steps to run the program:

• The project structure will look like this: 

• Run index.js file using below command: 

node index.js

Output:

Query {
  _mongooseOptions: {},
  _transforms: [],
  _hooks: Kareem { _pres: Map {}, _posts: Map {} },
  _executionCount: 0,
  op: undefined,
  options: {},
  _conditions: {},
  _fields: undefined,
  _update: undefined,
  _path: undefined,
  _distinct: undefined,
  _collection: undefined,
  _traceFunction: undefined,
  '$useProjection': true
}
Server listening on PORT 3000

Example 2: Filename: index.js

javascript

const mongoose = require('mongoose');

// Database connection
mongoose.connect('mongodb://127.0.0.1:27017/geeksforgeeks', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

// User model
const User = mongoose.model('User', {
    name: { type: String },
    age: { type: Number }
});

const query = new mongoose.Query();
query.collection(User.collection);
console.log(query);

Steps to run the program:

• The project structure will look like this: 

• Run index.js file using below command: 

node index.js

Output:

Query {
  _mongooseOptions: {},
  _transforms: [],
  _hooks: Kareem { _pres: Map {}, _posts: Map {} },
  _executionCount: 0,
  op: undefined,
  options: {},
  _conditions: {},
  _fields: undefined,
  _update: undefined,
  _path: undefined,
  _distinct: undefined,
  _collection: NodeCollection {
    collection: NativeCollection {
      collection: null,
      Promise: [Function: Promise],
      _closed: false,
      opts: [Object],
      name: 'users',
      collectionName: 'users',
      conn: [NativeConnection],
      queue: [],
      buffer: true,
      emitter: [EventEmitter]
    },
    collectionName: 'users'
  },
  _traceFunction: undefined,
  '$useProjection': true
}

Reference: https://mongoosejs.com/docs/api/query.html