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
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