Planned lessonJNR-030-L03

One-to-one

On This Lesson 4 topics

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In this lesson

map a one-to-one link and know its trade-offs.

@OneToOne with a unique foreign key column on the owning side.
Typical example: Customer and CustomerProfile.
Inverse (mappedBy) one-to-one cannot be lazy easily, because Hibernate must check if the row exists.
@MapsId shares the primary key with the parent and avoids a separate key.
Often an @Embeddable or a plain column set is simpler.

Draft outline details

java

@OneToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "customer_id", unique = true)
private Customer customer;

When might an embeddable be better than one-to-one?

Show answer

When the data has no identity and lives in the same table.

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