Answer
ObjectId is the default unique identifier for documents. It includes timestamp and machine-specific information to ensure global uniqueness.
Quick Answer
ObjectId is MongoDB's default primary key type - a 12-byte unique identifier automatically generated for the _id field. It encodes: 4-byte timestamp, 5-byte random value (unique per machine/process), 3-byte incrementing counter. This makes ObjectIds roughly sortable by creation time, unique across distributed systems, and generated client-side without DB round-trips.
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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