This post walks you through the process of mapping a many-to-many relationship with Spring Boot, Spring Data JPA and HSQL.

JPA Series with Spring Boot:
- JPA One-To-One Foreign Key Relationship Mapping Example with Spring Boot
- JPA One-To-One Shared Primary Key Relationship Mapping Example with Spring Boot
- JPA One-To-Many Relationship Mapping Example with Spring Boot
- JPA Many-To-Many Relationship Mapping Example with Spring Boot
- JPA Many-To-Many Extra Columns Relationship Mapping Example with Spring Boot

What you'll need

  • JDK 1.7 or later
  • Maven 3 or later

Stack

  • Spring Data JPA
  • Spring Boot

Project structure

├── src
│   └── main
│       ├── java
│       │   └── com
│       │       └── hellokoding
│       │           └── jpa
│       │               ├── model
│       │               │   ├── Book.java
│       │               │   └── Publisher.java
│       │               ├── repository
│       │               │   └── BookRepository.java
│       │               └── HelloJpaApplication.java
│       └──resources
│          └── application.properties
└── pom.xml

Project dependencies

Many-To-Many Relationship

The book and publisher tables have a many-to-many relationship via book_publisher table.

Define JPA Entities

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

@Table maps the entity with the table. If no @Table is defined, the default value is used: the class name of the entity.

@Id declares the identifier property of the entity.

@Column maps the entity's field with the table's column. If @Column is omitted, the default value is used: the field name of the entity.

@ManyToMany defines a many-to-many relationship between 2 entities. @JoinColumn indicates the entity is the owner of the relationship: 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 implemented some common functions to work with database: findOne, findAll, save,...All we need for this example is extend it.

Application Properties

Run the application

You can run the application using mvn spring-boot:run, JPA will insert data into book, publisher and book_publisher tables.

Source code

git@github.com:hellokoding/jpa-manytomany-springboot-hsql.git

https://github.com/hellokoding/jpa-manytomany-springboot-hsql

JPA Many-To-Many Examples:
- JPA Many-To-Many Relationship Mapping Example with Spring Boot
- JPA Many-To-Many Relationship Mapping Example with Spring Boot, Maven and MySQL
PersistenceJavaJPASpring BootHSQL