This tutorial will walk you through the steps of mapping a One To One bidirectional relationship of JPA/Hibernate entities with Spring Boot, MySQL and Docker.
JPA/Hibernate Entity Bidirectional Relationship Mapping Example Series with Spring Boot and MySQL
- JPA/Hibernate Composite Primary Key Example
- JPA/Hibernate One To One Bidirectional Relationship Mapping
- JPA/Hibernate One To One Shared Primary Key Bidirectional Relationship Mapping
- JPA/Hibernate One To Many Bidirectional Relationship Mapping
- JPA/Hibernate Many To Many Bidirectional Relationship Mapping
- JPA/Hibernate Many To Many Extra Columns Bidirectional Relationship Mapping
- Handling Circular Reference of JPA/Hibernate Entity Bidirectional Relationships with Jackson JsonIgnoreProperties
- JPA/Hibernate CRUD Example, Deleting Data with JPQL, CascadeType, and orphanRemoval
- Database Migration/Evolution Example with Flyway and JPA/Hibernate
What you will need
- Docker CE 18+
Project structure
Project dependencies
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 address.id.
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 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.
Application Properties
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/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
Testing time
Prepare Dockerfile for Java/Spring Boot application
Start your application and infrastructure via Docker Compose. Make sure your local Docker is running and your bash console is at the springboot-examples project root directory.
docker-compose -f docker-compose-jpa.yaml up --renew-anon-volumes one-to-one-foreign-key
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
That's it! Thanks for joining and have a happy coding. You can find the full source code as below
Source code
https://github.com/hellokoding/springboot-examples/tree/master/jpa-hibernate/one-to-one-foreign-key
You may also like
- Handling Circular Reference of JPA/Hibernate Entity Bidirectional Relationships with Jackson JsonIgnoreProperties
- JPA/Hibernate CRUD Example, Deleting Data with JPQL, CascadeType, and orphanRemoval