This tutorial will walk you through the steps of mapping a JPA/Hibernate One To Many bidirectional relationship with Spring Boot, Spring Data JPA, Lombok, 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'll need

  • Docker CE 18+

Project structure

Project dependencies


One-To-Many Relationship

One-to-many relationship refers to the relationship between two entities/tables A and B in which one element/row of A may be linked with many elements of B, but a member of B is linked to only one element of A.

In this example, the book_category and book tables have a one-to-many relationship. One category may be linked with many books but one book is linked to only one category.

book.book_category_id is a foreign key references to book_category.id

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.

@OneToMany and @ManyToOne defines a one-to-many and many-to-one relationship between 2 entities. @JoinColumn indicates the entity is the owner of the relationship and the corresponding table has a column with a foreign key to the referenced table. mappedBy indicates the entity is the inverse of the relationship.

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 Book will be saved at the same time with the owner BookCategory 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-many  

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-many

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