As of hibernate 5, the default identifier generator strategy is org.hibernate.id.enhanced.SequenceStyleGenerator, before it was native. Since MySQL has no physical sequences, the method BulkInsertionCapableIdentifierGenerator.supportsBulkInsertionIdentifierGeneration reports false for hibernate 5 which makes HqlSqlWalker.postProcessInsert#786 throw the exception that the generator does not support bulk insertions.
In hibernate <= 4.3 the IdentityGenerator was used which reported true thus making batch inserts possible. Maybe the default for databases that don't support sequences should stay native?
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