Hibernate: two List fetch joins in one query is MultipleBagFetchException

A List with no @OrderColumn is a 'bag' - unordered and duplicate-tolerant. Joining two bags produces a cartesian product Hibernate cannot unpick back into two collections, so it refuses at startup rather than returning wrong data.

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• Hibernate: equals/hashCode on a generated id breaks HashSet membership
• Hibernate: the first-level cache means a re-query never sees another transaction's update
• Hibernate: merge returns a copy, and the object you passed in stays detached

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Published 2026-08-25

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