The Java Persistence API specification imposes only a conditional requirement that ``++@Entity++`` classes be ``++Serializable++``:
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If an entity instance is to be passed by value as a detached object (e.g., through a remote interface), the entity class must implement the ``++Serializable++`` interface.
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But it's best practice to make all such classes ``++Serializable++`` from the start. So this rule raises an issue when an ``++@Entity++`` does not implement ``++Serializable++``.