JPA中的几个概念

Sky-Tiger

Lazy-loading relationships are a special case in the merge operation. If a lazy-loading relationship
was not triggered on an entity before it became detached, then that relationship will be
ignored when the entity is merged. If the relationship was triggered while managed and then
set to null while the entity was detached, then the managed version of the entity will likewise
have the relationship cleared during the merge.

Sky-Tiger

Lazy-loading relationships are a special case in the merge operation. If a lazy-loading relationship
was not triggered on an entity before it became detached, then that relationship will be
ignored when the entity is merged.

Sky-Tiger

We generally only cascade operations down from parent to child, not upwards
from child to parent. Doing so is not harmful but requires more effort from the persistence
provider to search out changes.