Is it Fine to store Mongo _id as a string, instead of ObjectId?

While it is technically possible to store the _id field in MongoDB as a string instead of an ObjectId, it is generally not recommended.

• The ObjectId is a special type of object that MongoDB uses to ensure uniqueness and provide some built-in functionality, such as sorting and indexing. When you use a string instead of an ObjectId, you lose some of these benefits.
• For example, sorting by _id will not work as expected if the _id is stored as a string. In addition, some MongoDB drivers may not handle string _id values correctly, which can lead to unexpected behavior.
• That being said, there may be some situations where storing _id as a string is acceptable, such as when integrating with an existing system that uses strings for identifiers. However, in general, it is recommended to use ObjectId for the _id field in MongoDB.

In MongoDB, the _id field is automatically created and assigned a unique ObjectId value when a new document is inserted. This ObjectId is a 12-byte value that includes a timestamp, a machine identifier, and a process identifier. Because the ObjectId is globally unique, it ensures that each document in a collection has a unique identifier.

When _id is stored as a string instead of an ObjectId, the uniqueness of the identifier is not guaranteed, and there may be a risk of collisions or duplication. This can cause problems when trying to retrieve specific documents from the collection, as you may not get the expected results.

In addition, ObjectId values have some built-in functionality that can be useful, such as the ability to sort documents by creation time. When _id is stored as a string, this functionality is lost, and you may need to implement your own sorting mechanism.

However, there may be situations where storing _id as a string makes sense. For example, if you are integrating with an existing system that already uses strings for document identifiers, it may be easier to store _id as a string in order to maintain compatibility. In general, though, it is recommended to use ObjectId for the _id field in MongoDB, as it provides better functionality and guarantees uniqueness.

Also, in MongoDB, the ObjectId is a binary data type. It is a 12-byte BSON (Binary JSON) value that consists of a 4-byte timestamp, a 3-byte machine identifier, a 2-byte process identifier, and a 3-byte counter.

Because ObjectId values are binary, they take up less space than equivalent string representations, making them more efficient to store and index. They also have a well-defined structure that ensures uniqueness, which makes them ideal for use as document identifiers.

In addition, MongoDB provides a number of built-in functions for working with ObjectId values, such as ObjectId() for creating new ObjectId values, ObjectId.isValid() for validating whether a string represents a valid ObjectId, and ObjectId.getTimestamp() for retrieving the timestamp associated with an ObjectId.

Overall, ObjectId values are a key part of the MongoDB data model, and they provide a reliable, efficient way to uniquely identify documents in a collection.