使用deleteOne()刪除單個(gè)文檔，適合刪除匹配條件的第一個(gè)文檔；使用deleteMany()刪除所有匹配的文檔。當(dāng)需要移除一個(gè)特定文檔時(shí)，應(yīng)使用deleteOne()，尤其在確定只有一個(gè)匹配項(xiàng)或只想刪除一個(gè)文檔的情況下有效。若要?jiǎng)h除多個(gè)符合條件的文檔，如清理舊日誌、測(cè)試數(shù)據(jù)等場(chǎng)景，應(yīng)使用deleteMany()。兩者均會(huì)永久刪除數(shù)據(jù)（除非有備份），且可能影響性能，因此應(yīng)在非高峰時(shí)段操作，並確保過(guò)濾條件準(zhǔn)確以避免誤刪。此外，刪除文檔不會(huì)立即減少磁盤(pán)文件大小，索引仍佔(zhàn)用空間直到壓縮。

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 precise, and always verify what will be deleted before executing these commands.

基本上就這些。

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