Deleting Documents in MongoDB

1. Introduction

In this tutorial, we will focus on how to delete documents in MongoDB. MongoDB is a popular NoSQL database that stores data in BSON format, which is a binary representation of JSON-like documents. Deleting documents is a crucial part of data management, and MongoDB provides two primary methods for this purpose: deleteOne() and deleteMany().

By the end of this tutorial, you will learn:

• How to use the deleteOne() method to delete a single document.
• How to use the deleteMany() method to delete multiple documents.
• Best practices when deleting documents.

There are no strict prerequisites for this tutorial, but it would be helpful if you have:

• Basic knowledge of MongoDB.
• MongoDB installed on your local machine.
• Basic knowledge of JavaScript, as we'll use it in our examples.

2. Step-by-Step Guide

In MongoDB, the deleteOne() function is used to delete the first document that matches the deletion criteria, while deleteMany() is used to delete all documents that match the deletion criteria.

2.1 deleteOne()

The deleteOne() function deletes the first document that matches a specified filter. Here's how it's used:

db.collection.deleteOne(query)

The query parameter is a filter that specifies the document to delete.

2.2 deleteMany()

The deleteMany() function deletes all documents that match a specified filter. Here's how it's used:

db.collection.deleteMany(query)

The query parameter is a filter that specifies the documents to delete.

3. Code Examples

Example 1: Using deleteOne()

In the following example, we'll delete a single document from the employees collection where name is 'John Doe':

// This is your MongoDB client
const MongoClient = require('mongodb').MongoClient;

// This is your connection string
const url = 'mongodb://localhost:27017/';

// Connect to the server
MongoClient.connect(url, function(err, db) {
  if (err) throw err;

  // This is your database
  const dbo = db.db('mydb');

  // This is your query
  const myquery = { name: 'John Doe' };

  // This is where you're deleting one document
  dbo.collection('employees').deleteOne(myquery, function(err, obj) {
    if (err) throw err;
    console.log('1 document deleted');
    db.close();
  });
});

Example 2: Using deleteMany()

In the following example, we'll delete all documents from the employees collection where name starts with the letter 'A':

// This is your MongoDB client
const MongoClient = require('mongodb').MongoClient;

// This is your connection string
const url = 'mongodb://localhost:27017/';

// Connect to the server
MongoClient.connect(url, function(err, db) {
  if (err) throw err;

  // This is your database
  const dbo = db.db('mydb');

  // This is your query
  const myquery = { name: /^A/ };

  // This is where you're deleting many documents
  dbo.collection('employees').deleteMany(myquery, function(err, obj) {
    if (err) throw err;
    console.log(obj.result.n + ' document(s) deleted');
    db.close();
  });
});

4. Summary

In this tutorial, we covered how to delete documents in MongoDB using deleteOne() and deleteMany(). We also walked through examples of how to use these methods.

Next, you might want to learn about other CRUD operations (Create, Update, Read) in MongoDB.

Here are a few additional resources:

• MongoDB Documentation
• MongoDB CRUD operations

5. Practice Exercises

Exercise 1: Delete a document from the students collection where age is less than 20.

Exercise 2: Delete all documents from the employees collection where salary is greater than 50000.

Exercise 3: Delete all documents from the products collection where name starts with the letter 'B'.

Practice is key to mastering any concept. Try to solve these exercises, and don't forget to check the MongoDB documentation if you're stuck. Happy learning!