In Mongoose, understanding the difference between `id` and `_id` is crucial for anyone working with MongoDB databases in their Node.js applications. These two properties may seem similar at first glance, but they serve different purposes and have distinct behaviors that you need to be aware of as a software developer. Let's dive into the details to demystify the dissimilarity between `id` and `_id`.
The `_id` field in MongoDB is a unique identifier generated by MongoDB for every document stored in a collection. This field is automatically created by the database system and serves as the primary key. It is a globally unique identifier, ensuring that each document has a distinct identifier within the collection. The `_id` field uses the ObjectID data type, which is a 12-byte identifier typically represented in hexadecimal format. MongoDB ensures the uniqueness of `_id` values across the collection, preventing any conflicts or duplicates.
On the other hand, the `id` field in Mongoose is a virtual getter for the `_id` field. When working with Mongoose models, you can access the `_id` value of a document using the more human-readable `id` property. Mongoose abstracts the complexity of dealing with MongoDB's `_id` field and provides a simplified interface using the `id` property to access the unique identifier of a document. The `id` property is not stored in the database; it is a computed property that maps to the `_id` field for convenience and ease of use in your application code.
One key distinction between `id` and `_id` is that MongoDB stores the `_id` field as an object with its own properties (e.g., timestamp, machine identifier, process identifier, and incrementing counter). In contrast, Mongoose's `id` property is a straightforward string representation of the `_id` value. When working with Mongoose schemas and models, you typically interact with the `id` property to reference the unique identifier of a document, while MongoDB manages the complexities of the underlying `_id` field.
It's essential to note that Mongoose automatically handles the conversion between the `id` and `_id` fields when interacting with documents in your application code. When you retrieve a document using Mongoose, you can access the `id` property to obtain the `_id` value. Similarly, when creating or updating documents, you can set the `id` property, and Mongoose will internally map it to the corresponding `_id` field in the MongoDB database.
In summary, the main difference between `id` and `_id` in Mongoose lies in their purposes and implementations. The `_id` field is a unique identifier created by MongoDB for each document, while the `id` property in Mongoose acts as a virtual getter for the `_id` field, providing a more user-friendly way to access the document's unique identifier. Understanding this distinction is essential for effectively working with Mongoose models and MongoDB databases in your Node.js applications.