How is id Generated in MongoDB
Last Updated :
24 Apr, 2024
In MongoDB, each document stored in a collection is uniquely identified by a field called _id. This _id field serves as the primary key for the document and is important for ensuring document uniqueness and efficient retrieval. But have you ever wondered how these _id values are generated in MongoDB?
In this article, we’ll explore the Complexities of MongoDB ID generation by covering concepts, and examples to provide a comprehensive understanding.
What is the _id Field in MongoDB?
- The
_id
field serves as the primary key for documents in a collection, ensuring each document has a unique identifier.
- MongoDB guarantees that each
_id
value is unique within a collection.
- If we don’t provide an
_id
field when inserting a document, MongoDB will automatically generate one for us . The default generation mechanism uses ObjectId
.
- The most common type of
_id
value is ObjectId
, which is a 12–byte identifier consisting of a timestamp, a random value, and an incrementing counter.
- While MongoDB provides automatic
_id
generation, we can also specify custom _id
values during document insertion, allowing us to use other data types such as strings or integers.
- The
_id
field is indexed by default, which can impact performance, especially when using custom _id
values or very large collections.
- MongoDB provides efficient ways to query documents by their
_id
values, making it easy to retrieve specific document
Generating an ObjectId
Let’s learn about how MongoDB generates an ObjectId. We can use the MongoDB shell to demonstrate this process.
Example of Generating an ObjectId
Open the MongoDB shell by running the Mongo command in your terminal or command prompt. Then, execute the following command to generate an ObjectId:
ObjectId()
Output:
ObjectId("62170c5af3d27e919f30b100")
In this example, MongoDB generates a new ObjectId with a unique value.
Custom _id Values
While MongoDB automatically generates ObjectId values for the _id field if one is not provided, we can also specify custom _id values during document insertion. This allows us to use other data types such as strings, integers, or even other objects as _id values.
Example of Specifying a Custom _id
db.users.insertOne({ _id: "user123", name: "John Doe", age: 30 })
In this example, we’re inserting a new document into the users collection with a custom _id value of “user123”.
Output:
{ "_id" : "user123", "name" : "John Doe", "age" : 30 }
Impact of _id Generation on Performance
MongoDB’s default _id generation strategy using ObjectId values provides several benefits, including:
- Uniqueness: ObjectId values are globally unique, ensuring document uniqueness across collections and databases.
- Scalability: ObjectId values are generated without the need for centralized coordination, making them suitable for distributed systems.
- Performance: The generation of ObjectId values is efficient, even at high write volumes.
Conclusion
Overall, Understanding how _id values are generated in MongoDB is essential for effectively managing and querying documents within collections. By default, MongoDB uses ObjectId values to uniquely identify documents, but you can also specify custom _id values to meet specific requirements. In this article, we explored the process of _id generation in MongoDB, covering concepts, examples, and outputs to provide beginners with a comprehensive understanding of this fundamental aspect of MongoDB document management. As you continue to work with MongoDB, mastering the generation and usage of _id values will empower you to build robust and efficient database solutions.
Share your thoughts in the comments
Please Login to comment...