关于MongoDB接收无_id字段文档时处理逻辑的技术问询

Hey there! Let me clear up this confusion for you based on MongoDB's core behavior:

Scenario 1: Document already includes an _id field (but not at the start) #

If you insert a document where the _id field exists but isn't the first field in the document, MongoDB's server will automatically reposition the _id field to the very beginning of the document. You don't need to manually adjust its position before insertion.

Scenario 2: Document does NOT include an _id field #

This is the part that confused you, so let's break it down clearly:

• You do NOT need to create or position the _id field yourself.
• MongoDB will automatically generate a unique ObjectId value for the _id field, and it will place this newly created field directly at the start of the document.

The mention of "moving the field to the start" in the docs for this scenario refers to MongoDB's own action of placing the auto-generated _id at the beginning, not a requirement for you to do so manually. You can safely insert documents without an _id field, and MongoDB handles the rest seamlessly.

内容的提问来源于stack exchange，提问作者jx2lee