JPA One To One unidirectional Mapping example

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/

Further Reading

Custom query with @Query annotation:
Spring JPA @Query example: Custom query in Spring Boot

If you want to add Pagination to this Spring project, you can find the instruction at:
Spring Boot Pagination & Filter example | Spring JPA, Pageable

To sort/order by multiple fields:
Spring Data JPA Sort/Order by multiple Columns | Spring Boot

Handle Exception for this Rest APIs is necessary:

• Spring Boot @ControllerAdvice & @ExceptionHandler example
• @RestControllerAdvice example in Spring Boot

Or way to write Unit Test for the JPA Repository:
Spring Boot Unit Test for JPA Repositiory with @DataJpaTest

You can also know:

• how to deploy this Spring Boot App on AWS (for free) with this tutorial.
• dockerize with Docker Compose: Spring Boot and MySQL example
• way to upload an Excel file and store the data in MySQL database with this post
• upload CSV file and store the data in MySQL with this post.

• Secure Spring Boot App with Spring Security & JWT Authentication
• Spring Data JPA Reference Documentation
• Spring Boot Pagination and Sorting example

Fullstack CRUD App:

• Vue + Spring Boot example
• Angular 8 + Spring Boot example
• Angular 10 + Spring Boot example
• Angular 11 + Spring Boot example
• Angular 12 + Spring Boot example
• Angular 13 + Spring Boot example
• Angular 14 + Spring Boot example
• React + Spring Boot example

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:

• Spring JPA + H2 example
• Spring JPA + MySQL example
• Spring JPA + PostgreSQL example
• Spring JPA + Oracle example
• Spring JPA + SQL Server example

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