In this tutorial, I will show you how to implement Spring JPA One-To-One unidirectional mapping with Hibernate in a Spring Boot example using @OneToOne annotation. You'll know:

How to configure Spring Data, JPA, Hibernate to work with Database
How to define Data Models and Repository interfaces for JPA One-To-One relationship
Way to use Spring JPA to interact with Database for One-To-One association
Way to create Spring Rest Controller to process HTTP requests

Full article at: https://www.bezkoder.com/jpa-one-to-one/

Appropriate way to implement JPA/Hibernate One To One mapping

In a relational database, a One-to-One relationship between table A and table B indicates that one row in table A links to only one row in table B, and vice versa.

For example, you need to design data model for a Tutorial Blog in which One Tutorial has corresponding Details (the Date Time it was created on, the author it was created by). So this is a One-to-One association.

You can use a Join Table (with @JoinTable annotation). It stores the primary key values from both entities in a NEW table.

Another way is to use Shared Primary Key with the Foreign Key is located in the tutorial_details table. Tutorial entity is the parent, and the Tutorial Details is the child.

You can map the child entity with the parent using JPA/Hibernate @OneToOne annotation. And in this case, only the children-side defines the relationship. We call it unidirectional One-to-One association.

Now look at the tutorial_details table that contains a Primary Key column (id) and a Foreign Key column (tutorial_id). You can see that we really need only one tutorial_details (child) row associated with a tutorial (parent) row, and the child data is hardly used in other relationships. So we can omit the child's id column:

JPA One To One example

We're gonna create a Spring project from scratch, then we implement JPA/Hibernate One to One Unidirectional Mapping with tutorials and tutorial_details table as following:

We also write Rest Apis to perform CRUD operations on the Details entities.

These are APIs that we need to provide:

Methods	Urls	Actions
POST	/api/tutorials/:id/details	create new Details for a Tutorial
GET	/api/details/:id	retrieve Details by `:id`
GET	/api/tutorials/:id/details	retrieve Details of a Tutorial
PUT	/api/details/:id	update Details by `:id`
PUT	/api/tutorials/:id/details	update Details of a Tutorial
DELETE	/api/details/:id	delete Details by `:id`
DELETE	/api/tutorials/:id/details	delete Details of a Tutorial
DELETE	/api/tutorials/:id	delete a Tutorial (and its Details)

Assume that we've had tutorials table like this:

Here are the example requests:

Create new Details entity: POST /api/tutorials/[:id]/details

tutorial_details table after that:

Retrieve Details of specific Tutorial: GET /api/tutorials/[:id]/details or /api/details/[:id]

Update Details of specific Tutorial: PUT /api/tutorials/[:id]/details or /api/details/[:id]

Delete Details of specific Tutorial: DELETE /api/tutorials/[:id]/details or /api/details/[:id]

Check the tutorial_details table, row with tutorial_id=1 were deleted:

Delete a Tutorial: DELETE /api/tutorials/[:id]

Tutorial (id=3) and its Details were deleted:

Let's build our Spring Boot Data JPA One to One example.

Spring Boot One to One example

Technology

Java 8
Spring Boot 2.7.2 (with Spring Web MVC, Spring Data JPA)
H2/MySQL/PostgreSQL
Maven 3.8.1

Project Structure

Let me explain it briefly.

– Tutorial, TutorialDetails data model class correspond to entity and table tutorials, tutorial_details.
– TutorialRepository, TutorialDetailsRepository are interfaces that extends JpaRepository for CRUD methods and custom finder methods. It will be autowired in TutorialController, TutorialDetailsController.
– TutorialController, TutorialDetailsController are RestControllers which has request mapping methods for RESTful CRUD API requests.
– Configuration for Spring Datasource, JPA & Hibernate in application.properties.
– pom.xml contains dependencies for Spring Boot and MySQL/PostgreSQL/H2 database.

– About exception package, to keep this post straightforward, I won't explain it. For more details, you can read following tutorial:
@RestControllerAdvice example in Spring Boot

Step by step and Github source code can be found at:
https://www.bezkoder.com/jpa-one-to-one/

Source Code

You can find the complete source code for this tutorial on Github.

One-to-Many: JPA One To Many example with Hibernate and Spring Boot
Many-to-Many: JPA Many to Many example with Hibernate in Spring Boot

You can apply this implementation in following tutorials:

More Derived queries at:
JPA Repository query example in Spring Boot

JPA One To One unidirectional Mapping example