So far, we handed the plain instance deserialized from the request body to the repository to persist it. That caused issues in PUT for create scenarios where the URI contains the identifier to be used for the aggregate to create and identifier generation being used in the backend. In that case the identifier submitted was never considered and subsequent requests would've created new instances, effectively breaking the idempotent nature of PUT.
We now make sure the backend identifier derived from the resource is set on the aggregate instance about to be created, so that backend can either accept that situation (new entity + manually defined identifier) or reject it (in case it insists on identifier generation).
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