This tutorial will walk you through the steps of mapping a JPA and Hibernate One To One bidirectional entity relationships example with Spring Boot, Spring Data JPA, Lombok, MySQL and Docker

What you will need

  • JDK 8+ or OpenJDK 8+
  • Maven 3+
  • MySQL Server 5+ or Docker CE 18+

Init project structure and dependencies

Project structure

├── src
│   └── main
│       ├── java
│       │   └── com
│       │       └── hellokoding
│       │           ├── jpa
│       │           │   ├── book
│       │           │   │   ├──
│       │           │   │   ├──
│       │           │   │   ├──
│       │           │   │   └──
│       │           │   └──
│       │           └── springboot
│       └── resources
│           └──
├── Dockerfile
├── docker-compose.yml
└── pom.xml

Project dependencies

Define JPA Entities and Repositories

One-To-One Relationship

One to one relationship refers to the relationship between two entities/tables A and B in which one item/row of A may be linked with only one item/row of B, and vice versa.

In this example, library and address tables have a one-to-one relationship. A library has only one address, and an address is the address of only one library.

library.address_id is a foreign key references to

Try this example if the relationship owner uses its foreign key as primary key
JPA/Hibernate One To One Shared Primary Key Bidirectional Relationship Mapping

Define JPA and Hibernate Entities

JPA Entity is defined with @Entity annotation, represent a table in your database.

@Id declares the entity identifier.

@Column maps the entity's field with the table's column. If @Column is omitted, the field name of the entity will be used as column name by default.

@OneToOne defines a one-to-one relationship between 2 entities.

@JoinColumn defines foreign key column and indicates the owner of the relationship.

mappedBy indicates the inverse of the relationship.

unique = true enforces the unique constraint, 1 address belongs to only 1 library.

Spring Data JPA Repository

Spring Data JPA contains some built-in Repository abstracting common functions based on EntityManager to work with database such as findAll, findById, save, delete, deleteById. All we need for this example is extends JpaRepository.

Define properties and creating data

Application Properties

hk-mysql refers to Docker Compose service defined in the below docker-compose.yml file

spring.jpa.hibernate.ddl-auto=create allows JPA/Hibernate auto create database and table schema for you.

On production environment, you may like to disable the DDL Auto feature by using spring.jpa.hibernate.ddl-auto=validate or spring.jpa.hibernate.ddl-auto=none (default). Check out this example as one of the approaches
Database Migration/Evolution Example with Flyway and JPA/Hibernate

Creating data with JPA and Hibernate

Thanks to CascadeType.ALL, associated entity Address will be saved at the same time with the owner Library without the need of calling its save function explicitly

Run the example

Run with Docker

Prepare Dockerfile for Java/Spring Boot application and docker-compose.yml for MySQL Server

Type the below command at the project root directory, make sure your local Docker is running

docker-compose up  

Access to MySQL Server docker container by issuing below bash command and key in hellokoding on Enter password:

docker exec -it hk-mysql mysql -p

Query schema and data created by JPA/Hibernate based on your mapping

Run with JDK/OpenJDK, Maven and MySQL Server local

Update hk-mysql on to localhost and type the below command at the project root directory

mvn clean spring-boot:run  

Source code

See also