Supported

Composite primary keys declared with @EmbeddedId (a plain @Embeddable). @Struct on the id embeddable is neither required nor needed.

The key is stored as the document's _id sub-document, with a stable field order. For an entity keyed on (publisherId, bookNo):

{ "_id": { "publisherId": 1, "bookNo": 1 }, "title": "..." }

Application-assigned only (composite keys are never generated).

Operations:

• persist / find / update / delete by id
• HQL filtering by the whole id (=, in) and by individual id fields
• selecting the id or an id field
• order by id
• bulk update / delete by id

Associations to a composite-key entity depend on HIBERNATE-164 (compound equijoin ON); end-to-end support to be verified once 164 lands.

Out of scope

• @jakarta.persistence.IdClass composite keys