MongoDB · question
Question 5 of 52
What is ObjectId in MongoDB?
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Re-explain
ObjectId is a 12-byte unique identifier used as the default value for the _id field.
Structure (24 hex characters):
- 4 bytes: Unix timestamp
- 5 bytes: Random unique value
- 3 bytes: Incrementing counter
Properties:
- Automatically generated if not provided
- Contains creation timestamp
- Globally unique across machines
- Sortable by creation time
// ObjectId example
ObjectId("507f1f77bcf86cd799439011")
// Extract timestamp
ObjectId("507f1f77bcf86cd799439011").getTimestamp()
// Returns: ISODate("2012-10-17T20:46:47Z")
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