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Mongoose Aggregate.prototype.exec() API

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  • Last Updated : 07 Dec, 2022
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The Aggregate API.prototype.exec() method of the Mongoose API is used to perform aggregation tasks. It allows us to execute the aggregate pipeline on the current Model. It takes a callback function as a parameter and returns a promise.

Syntax:

aggregate.exec( callback )

Parameters: This method accepts a single parameter as discussed below:

  • callback: It is used to handle the promise returned by the method.

Return Value: This method returns a promise which can be handled using callback function or using async-await.

Setting up Node.js application:

Step 1: Create a Node.js application using the following command:

npm init

Step 2: After creating the NodeJS application, Install the required module using the following command:

npm install mongoose

Project Structure: The project structure will look like this: 

 

Database Structure: The database structure will look like this, the following documents are present in the collection.

 

Example 1: In this example, we have established a database connection using mongoose and defined model over cricketerSchema, having three columns or fields “_id”, “name”, and “nationality”. At the end, we have added pipeline operation to select name field from the collection. And we are calling exec() method to get the result set.

Filename: app.js

Javascript




// Require mongoose module
const mongoose = require("mongoose");
  
// Set Up the Database connection
    useNewUrlParser: true,
    useUnifiedTopology: true,
});
  
const cricketerSchema = new mongoose.Schema({
    _id: Number,
    name: String,
    nationality: String
});
  
const Cricketer = mongoose.model('Cricketers', cricketerSchema);
  
Cricketer
    .aggregate([{ $project: { name: 1 } }])
    .exec((error, result) => {
        if (error) {
            console.log(error);
        } else {
            console.log(result);
        }
    })


Step to run the program: To run the application execute the below command from the root directory of the project:

node app.js

Output:

[
  { _id: 3, name: 'Ben Stokes' },   
  { _id: 2, name: 'David Warner' }, 
  { _id: 5, name: 'Aaron Finch' },  
  { _id: 7, name: 'K L Rahul' },    
  { _id: 6, name: 'Hardik Pandya' },
  { _id: 1, name: 'Virat Kohli' },  
  { _id: 4, name: 'Rohit Sharma' }  
]

Example 2: In this example, we have established a database connection using mongoose and defined model over cricketerSchema, having three columns or fields “_id”, “name”, and “nationality”. At the end, we are handling the promise returned by exec() method using asynchronous function and await keyword.

Filename: app.js

Javascript




// Require mongoose module
const mongoose = require("mongoose");
  
// Set Up the Database connection
    useNewUrlParser: true,
    useUnifiedTopology: true,
});
  
const cricketerSchema = new mongoose.Schema({
    _id: Number,
    name: String,
    nationality: String
});
  
const Cricketer = mongoose.model('Cricketers', cricketerSchema);
  
const execExample = async () => {
    const result = await Cricketer
        .aggregate([{
            $project: { nationality: 1, _id: 0, name: 1 }
        }])
        .exec();
    console.log(result);
}
execExample();


Step to run the program: To run the application execute the below command from the root directory of the project:

node app.js

Output:

[
  { name: 'Ben Stokes', nationality: 'England ' },   
  { name: 'David Warner', nationality: 'Australia' },
  { name: 'Aaron Finch', nationality: 'Australia ' },
  { name: 'K L Rahul', nationality: 'India ' },      
  { name: 'Hardik Pandya', nationality: 'India ' },  
  { name: 'Virat Kohli', nationality: 'India' },     
  { name: 'Rohit Sharma', nationality: 'India ' }    
]

Reference: https://mongoosejs.com/docs/api/aggregate.html#aggregate_Aggregate-exec


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