21.17.1. What isn’t and will not be supported

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Bags are not supported because they can contain non-unique elements.
Persisting, a bag of `String`s violates the relational database principle that each table is a set of tuples.

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In case of bags, however (which require a join table), if there is a duplicate element, the two tuples corresponding to the elements will be the same.
Hibernate allows this, however Envers (or more precisely: the database connector) will throw an exception when trying to persist two identical elements because of a unique constraint violation.

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There are at least two ways out if you need bag semantics:

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1. use an indexed collection, with the @javax.persistence.OrderColumn annotation
2. provide a unique id for your elements with the @CollectionId annotation. </div> </div>