Unlock the Power of MongoDB: Learn How to Create Primary Keys with These Easy Code Examples.

Table of content

  1. Introduction
  2. What is MongoDB?
  3. Why Use Primary Keys?
  4. Creating Primary Keys in MongoDB
  5. Creating a Primary Key in the MongoDB Shell
  6. Creating a Primary Key in Python Using PyMongo
  7. Creating a Primary Key in Node.js Using the MongoDB Driver
  8. Best Practices for Primary Keys in MongoDB
  9. Conclusion
  10. Additional Resources (optional)


If you are looking for a database that is flexible, scalable, and easy to use, MongoDB is a popular choice for many developers. One key feature of MongoDB is the ability to create primary keys for your data, which can help ensure the uniqueness of your records and improve the performance of your queries.

In this article, we will provide you with an overview of primary keys and how they work in MongoDB. We will also give you some easy-to-follow code examples that you can use to create primary keys in your own MongoDB applications.

Whether you are a beginner or an experienced developer, this guide can help you unlock the power of MongoDB and take your applications to the next level. So let's get started and learn how to create primary keys with MongoDB!

What is MongoDB?

MongoDB is a popular document-oriented NoSQL database. "NoSQL" refers to non-relational databases, which means that they do not use the traditional table structure found in relational databases like SQL. Instead, NoSQL databases like MongoDB store data in flexible, semi-structured documents that can be easily modified and expanded over time.

MongoDB has become a popular choice for many developers who prefer its flexible data model and dynamic schema. It is particularly well-suited for large-scale applications that need to handle complex and unstructured data sets, such as social media platforms, e-commerce sites, and IoT applications.

Here are a few key features of MongoDB:

  • Flexible schema: MongoDB allows developers to store data in a dynamic and flexible manner, making it easy to modify and update databases without needing to redefine the entire schema.

  • JSON-based documents: MongoDB stores data in JSON-like documents, which are human-readable and easy to work with. This also makes it easy to integrate MongoDB with other web technologies.

  • Horizontal scalability: MongoDB is designed to scale horizontally, allowing developers to add more servers to handle increased traffic and data volumes.

  • Indexing: MongoDB supports a variety of indexing capabilities, helping to optimize query performance and improve the speed of database operations.

Overall, MongoDB offers a powerful and flexible database solution that can help developers build robust and scalable applications.

Why Use Primary Keys?

A primary key is a field that uniquely identifies each record in a database table. Here are some reasons why primary keys are important for effective data management:

  • Uniqueness: Primary keys ensure that each record in a table is unique and can be identified easily.
  • Efficiency: Without primary keys, searching for a specific record in a large table can be time-consuming and resource-intensive.
  • Data Consistency: Primary keys can help maintain data integrity by preventing duplicate records and ensuring that each record has a unique identity.
  • Foreign Key Relationships: Primary keys are often used as the basis for establishing relationships between tables in a database.

By using primary keys, you can improve the overall efficiency and reliability of your database. For example, when you need to update or delete a record, you can easily identify it using the primary key. Additionally, primary keys make it easier to establish relationships between tables, which is essential for complex databases with multiple related tables.

In MongoDB, primary keys are known as "_id" fields. By default, MongoDB creates an "_id" field for each record in a collection, which acts as the primary key. However, you can also create custom primary keys to suit the specific needs of your application.

Creating Primary Keys in MongoDB


In MongoDB, primary keys (also known as "_id") are automatically created for each document in a collection, but sometimes developers need more control over this process. There are several ways to create primary keys in MongoDB, including:

###Creating a Primary Key with ObjectId()

One common way to create primary keys in MongoDB is by using a function called ObjectId(). This function creates a unique 12-byte hexadecimal string that is guaranteed to be unique on the machine and within the same second.

To use this function in your code, simply call it when creating a new document:

    _id: ObjectId(),
    name: "John",
    age: 30 

###Creating a Primary Key with a Custom Value

If you want to create a primary key with a specific value, you can do so by passing the value as a parameter when creating the document:

    _id: "ABC123",
    name: "John",
    age: 30 

Keep in mind that using custom values for primary keys can cause problems if not properly managed. It's best to use autogenerated primary keys whenever possible.


is an important part of developing scalable and efficient applications. With the methods described above, developers can create unique primary keys that allow for easy data retrieval and management. By using autogenerated primary keys, developers can ensure that their data is properly indexed and avoid potential issues caused by duplicate values.

Creating a Primary Key in the MongoDB Shell

When creating a new collection in MongoDB, you can specify a primary key for that collection. A primary key is a unique identifier for each document in the collection and is used to ensure that the collection remains organized and that each document can be accessed quickly and efficiently.

To create a primary key in the MongoDB shell, follow these steps:

  1. Open the MongoDB shell and select the database where you want to create the collection.
  2. Type db.createCollection() and specify the name of the collection you want to create. You can also include options for the collection, such as the maximum number of documents or the size of the collection.
  3. Specify the primary key when you create the collection by including { "_id": 1 } as an argument in the createCollection() method. This will create a primary key field called _id and set the value of the field to 1.
  4. Add documents to the collection using the insert() method. When adding new documents, you do not need to specify a value for the primary key field. MongoDB will automatically generate a unique value for the _id field for each new document.

Here is an example of how to create a collection with a primary key in the MongoDB shell:

> use mydb
switched to db mydb
> db.createCollection("mycollection", { capped: true, size: 100000})
{ "ok" : 1 }
> db.createCollection("mycollection", { _id: 1 })
{ "ok" : 1 }
> db.mycollection.insert({ name: "John", age: 25 })
WriteResult({ "nInserted" : 1 })

In this example, we created a new collection called mycollection in the mydb database with a primary key set to _id. We also specified options for the collection, such as the maximum size of the collection. Finally, we inserted a new document into the collection without specifying a value for the _id field. MongoDB automatically generated a unique value for the _id field for the new document.

Creating a Primary Key in Python Using PyMongo

PyMongo is a popular third-party Python package that allows developers to interact with MongoDB in a Python application. When creating documents in MongoDB, it's important to ensure each document has a primary key. A primary key is a unique identifier for each document in a MongoDB collection, and it helps maintain data integrity and database performance. Here's how to create a primary key in Python using PyMongo.

Step 1: Connect to MongoDB

Before we can create a primary key in Python, we need to connect to a MongoDB database using PyMongo. Here's an example of how to do that:

import pymongo

# Create a MongoClient object
client = pymongo.MongoClient("mongodb://localhost:27017/")

# Get the "mydatabase" database
db = client["mydatabase"]

Step 2: Insert a Document

Next, we need to insert a document into a MongoDB collection. Here's an example:

# Get the "customers" collection
col = db["customers"]

# Create a document with a primary key
customer = {"_id": 1, "name": "John"}

# Insert the document into the collection

Note that we've included an "_id" field with a value of 1 to create a primary key for the document. If we try to insert another document with the same "_id" value, MongoDB will throw an error.

Step 3: Generate a Unique ID

If we don't have an appropriate unique identifier for our document, we can generate a new ObjectId using PyMongo. Here's an example:

# Generate a new ObjectId
from bson.objectid import ObjectId

id = ObjectId()

# Create a document with the new ObjectId
customer = {"_id": id, "name": "Jane"}

# Insert the document into the collection

This creates a new ObjectId, which can be used as a primary key in our MongoDB collection.

is simple and straightforward. By following the steps outlined above, you can ensure your MongoDB database has a unique identifier for each document, which will help maintain data integrity and database performance.

Creating a Primary Key in Node.js Using the MongoDB Driver

In MongoDB, every document must have a unique identifier, known as a primary key. This primary key is used to identify and label documents within a collection, and it ensures that each document can be accessed easily and efficiently. In Node.js, you can create a primary key using the MongoDB driver, which is a powerful tool that allows you to interact with MongoDB databases and collections directly from your Node.js application.

To create a primary key in Node.js using the MongoDB driver, follow these simple steps:

  1. First, define your primary key field. In most cases, this will be a unique identifier such as an email address or username. You can define this field using the "_id" property.
const user = {_id: 'john.doe@example.com', name: 'John Doe'}
  1. Next, connect to your MongoDB database using the MongoClient from the MongoDB driver.
const MongoClient = require('mongodb').MongoClient;
const uri = "mongodb+srv://<cluster>.mongodb.net/<db>?retryWrites=true&w=majority";
const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true });
  1. Once you are connected to your database, you can insert your document into a collection using the insertOne() method.
client.connect(err => {
  const collection = client.db("test").collection("users");
  collection.insertOne(user, function(err, res) {
    console.log("Document inserted.");
  1. Finally, verify that your primary key is working correctly by querying the collection for a specific document using the findOne() method.
client.connect(err => {
  const collection = client.db("test").collection("users");
  collection.findOne({_id: 'john.doe@example.com'}, function(err, res) {

By following these steps, you can easily create a primary key in Node.js using the MongoDB driver. With this primary key, you can ensure that your documents are easily accessible and identifiable, and you can streamline your MongoDB queries and operations for maximum efficiency.

Best Practices for Primary Keys in MongoDB

When working with MongoDB, it's important to use primary keys in order to uniquely identify each document in your collections. Here are some best practices to keep in mind when creating primary keys in MongoDB:

Use ObjectIds as Primary Keys

ObjectIds are automatically generated by MongoDB and provide a globally unique identifier for each document. They are easy to use and don't require any additional configuration. Here's an example of how to create a new document with an ObjectId as its primary key:

db.collection.insertOne({ _id: ObjectId(), name: "John Doe" });

Consider Using Application-Specific Values

In some cases, it may be appropriate to use application-specific values as primary keys. For example, if you were building a social media application, you might use a combination of the user's username and the post's timestamp as the primary key for each post. Just keep in mind that using application-specific values may require additional logic to ensure uniqueness.

Avoid Using Sequential Numbers as Primary Keys

While it may be tempting to use sequential numbers as primary keys to make it easier to retrieve documents in the order they were created, doing so can lead to performance issues at scale. When you insert a new document, MongoDB has to find the next sequential number before inserting the document, which can slow down your writes.

Keep Primary Keys Small

It's generally a good idea to keep primary keys small, since they are used in many places throughout MongoDB. In particular, smaller primary keys can improve performance by reducing the amount of data that needs to be loaded into memory.

By keeping these best practices in mind, you can ensure that your MongoDB collections are well-designed and performant.


In this article, we've explored the concept of primary keys in MongoDB and how they can be utilized in Android application development. Primary keys are essential for managing data efficiently, ensuring data integrity and facilitating data retrieval. By creating primary keys, you can also easily update, delete, and query your database documents.

We discussed three approaches to create primary keys in MongoDB, which include:

  • ObjectIds
  • UUIDs
  • Custom keys

ObjectIds are the most common keys used in MongoDB, and they provide a simple and efficient way of generating unique IDs. UUIDs are also an excellent alternative if you need to generate IDs that are independent of the underlying platform or programming language. Custom keys offer flexibility, but they require careful planning to ensure uniqueness.

We also provided code examples of how to create primary keys using these approaches, which should help you get started with using primary keys in your Android application development. By implementing primary keys, you are on your way to building a robust and scalable database system for your Android application.

In , primary keys are a fundamental aspect of MongoDB and Android application development. They provide a way to uniquely identify and manage data, ensuring data accuracy, consistency, and reliability. By applying the knowledge you've gained in this article, you will be able to harness the power of MongoDB to create efficient and functional Android applications.

Additional Resources (optional)

If you're interested in learning more about creating primary keys in MongoDB, there are a number of additional resources available that can help you deepen your understanding of this topic. Here are a few resources to consider:

  • The MongoDB documentation: The official documentation for MongoDB is a great place to start if you're looking to learn more about creating primary keys in this database management system. The documentation includes detailed explanations and code examples that can help you get started with using primary keys in your own MongoDB applications.

  • Online tutorials: There are many online tutorials available that can help you learn how to create primary keys in MongoDB. Some of the most popular resources include tutorials on sites like Udemy, Pluralsight, and Codecademy.

  • Books: There are also a number of books available that provide detailed information on using MongoDB, including creating primary keys. Some popular options include "MongoDB: The Definitive Guide" by Kristina Chodorow, "MongoDB in Action" by Kyle Banker, and "MongoDB Applied Design Patterns" by Rick Copeland.

  • Community forums: Finally, if you're looking for help with creating primary keys in MongoDB, there are many online forums where you can connect with other developers who have experience using this database management system. Some popular options include the MongoDB Community Forum, Reddit's /r/mongodb, and the MongoDB User Group on LinkedIn.

Cloud Computing and DevOps Engineering have always been my driving passions, energizing me with enthusiasm and a desire to stay at the forefront of technological innovation. I take great pleasure in innovating and devising workarounds for complex problems. Drawing on over 8 years of professional experience in the IT industry, with a focus on Cloud Computing and DevOps Engineering, I have a track record of success in designing and implementing complex infrastructure projects from diverse perspectives, and devising strategies that have significantly increased revenue. I am currently seeking a challenging position where I can leverage my competencies in a professional manner that maximizes productivity and exceeds expectations.
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