Answer
Every document has a unique _id field, which acts as the primary key. MongoDB generates an ObjectId if not provided.
Quick Answer
Every MongoDB document has an _id field that serves as the primary key - it must be unique within the collection. By default, MongoDB auto-generates an ObjectId for _id. You can provide your own _id value (string, int, etc.) but it must be unique. The _id field is always indexed automatically.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ