The Query.prototype.$where() specifies a JavaScript function or expression to pass to MongoDB’s query system. Using this, the where condition can be customized according to the need of the user.
Syntax:
Query.prototype.$where()
Parameters: This function has one parameter js i.e. JavaScript string or function.
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
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:
Project Structure: The project structure will look like this:
Example 1:
Filename: index.js
const mongoose = require( 'mongoose' );
// Database connection useNewUrlParser: true ,
useCreateIndex: true ,
useUnifiedTopology: true
}); // User model const User = mongoose.model( 'User' , {
name: { type: String },
age: { type: Number }
}); const query = User.find(); query.collection(User.collection); query.$where( function () {
if ( this .age < 100) return true ;
else return false ;
}) query.where( 'age' ).gte(1).exec( function (error, result) {
if (error) {
console.log(error)
} else {
console.log(result)
}
}); |
Run index.js file using below command:
node index.js
Output:
[ { _id: 5ebb9129a99bde77b2efb809, name: 'Gourav', age: 10, __v: 0 }, { _id: 5ebc3669a99bde77b2efb9ba, name: 'Lalit', age: 25, __v: 0 }, { _id: 5ebc367da99bde77b2efb9bf, name: 'Piyush', age: 5, __v: 0 }, { _id: 5ebd345f5d2d8a3534b2f391, name: 'Manish', age: 34, __v: 0 } ]
Example 2:
Filename: index.js
const mongoose = require( 'mongoose' );
// Database connection useNewUrlParser: true ,
useCreateIndex: true ,
useUnifiedTopology: true
}); // User model const User = mongoose.model( 'User' , {
name: { type: String },
age: { type: Number }
}); const query = User.find(); query.collection(User.collection); query.$where( function () {
if ( this .age < 100) return false ;
else return true ;
}) query.where( 'age' ).gte(1).exec( function (error, result) {
if (error) {
console.log(error)
} else {
console.log(result)
}
}); |
Run index.js file using below command:
node index.js
Output:
[]
Reference:
https://mongoosejs.com/docs/api/query.html#query_Query-$where