Populating a Child-Side Parent Association via Proxy

Description: A Proxy can be useful when a child entity can be persisted with a reference to its parent. In such cases, fetching the parent entity from the database (execute the SELECT statement) is a performance penalty and a pointless action. Hibernate can set the underlying foreign key value for an uninitialized Proxy.

Key points:
- rely on EntityManager#getReference()
- in Spring, use JpaRepository#getOne() -> used in this example
- in Hibernate, use load()
- here, we have two entities, Tournament and TennisPlayer, and a tournament can have multiple players (@OneToMany)
- we fetch the tournament via a Proxy (this will not trigger a SELECT), we create a new tennis player, we set the Proxy as the tournament for this player and we save the player (this will trigger an INSERT in the tennis players table, tennis_player)

Output example:
- the console output will reveal that only an INSERT is triggered, not the SELECT