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 Databas…


This content originally appeared on DEV Community 👩‍💻👨‍💻 and was authored by Tien Nguyen

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.

jpa-hibernate-one-to-one-join-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.

jpa-hibernate-one-to-one

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-hibernate-one-to-one-example

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:

jpa-hibernate-one-to-one-example

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:

jpa-hibernate-one-to-one-parent-table

Here are the example requests:

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

jpa-hibernate-one-to-one-create

tutorial_details table after that:

jpa-hibernate-one-to-one-table

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

jpa-hibernate-one-to-one-retrieve

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

jpa-hibernate-one-to-one-update

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

jpa-hibernate-one-to-one-delete

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

jpa-hibernate-one-to-one-delete-db

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

jpa-hibernate-one-to-one-delete-parent

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

jpa-hibernate-one-to-one-delete-parent-table

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

spring-data-jpa-one-to-one-unidirectional

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:

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

You can also know:

Fullstack CRUD App:

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


This content originally appeared on DEV Community 👩‍💻👨‍💻 and was authored by Tien Nguyen


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