In 2.6 a db.collection.update() upsert with a dotted path _id specification would complete successfully, in 3.0 this behavior has changed, though it is inconsistent between updates and upserts.
While this behavior is intentional (SERVER-14973), it may cause failures in applications that have inconsistent object notations.
- related to
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SERVER-14973 Support $eq with sharding
- Closed