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Use deleteOne() to delete a single document, which is suitable for deleting the first document that matches the criteria; use deleteMany() to delete all matching documents. When you need to remove a specific document, deleteOne() should be used, especially if you determine that there is only one match or you want to delete only one document. To delete multiple documents that meet the criteria, such as cleaning old logs, test data, etc., deleteMany() should be used. Both will permanently delete data (unless there is a backup) and may affect performance, so it should be operated during off-peak hours and ensure that the filtering conditions are accurate to avoid mis-deletion. Additionally, deleting documents does not immediately reduce disk file size, and the index still takes up space until compression.

When you're working with MongoDB and need to remove documents from a collection, deleteOne() and deleteMany() are two of the most commonly used methods. They're straightforward but knowing when and how to use them effectively can prevent mistakes and improve performance.

Use deleteOne() to Remove a Single Document

This method is ideal when you want to delete one specific document that matches a given filter. It removes the first matching document it finds — not necessarily based on your intended order unless you specify it.

For example, if you have a collection of users and want to delete a user with a specific email:

 db.users.deleteOne({ email: "test@example.com" });

If there are multiple users with that email, only one will be deleted. This makes deleteOne() useful when:

• You're certain there's only one match.
• You want to safely delete just one document even if duplicates exist.

A good practice is to include a unique field like _id or another identifier to ensure you're targeting the correct document.

Apply deleteMany() for Bulk Deletion

Use deleteMany() when you need to delete all documents that match a certain condition. For instance, if you want to delete all inactive users:

 db.users.deleteMany({ status: "inactive" });

This operation is powerful and should be used carefully, especially in production environments. Some typical uses include:

• Cleaning up old logs or expired data.
• Removing test entries after development or testing phases.
• Deleting all records related to a specific category or user.

Always double-check your filter before running deleteMany() . Once deleted, the data won't be recoverable unless you have backups or replication enabled.

Considerations When Deleting Documents

There are a few important things to keep in mind:

• Deleted documents are permanently removed unless your database has some form of versioning or snapshotting.
• Both operations affect performance if run on large collections. Try to avoid deleting large volumes of data during peak hours.
• If you're using replica sets or sharded clusters, deletions are propagated accordingly, so make sure this aligns with your system design.

Also, remember:

• Indexes still take up space until compacted.
• Deleted documents free up storage but don't reduce the overall file size on disk immediately.

Final Thoughts

Using deleteOne() and deleteMany() correctly depends largely on understanding your data and the consequences of deletion. Make sure your filters are precision, and always verify what will be deleted before executing these commands.

Basically that's it.

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