Spring Boot: JPA Mappings

Spring Boot JPA Relationships and Mappings

Spring-Boot

JPA

Spring Boot JPA

Author

albertprofe

Published

Tuesday, June 1, 2021

Modified

Saturday, September 7, 2024

📘 JPA Mappings and relationships

Spring Boot provides an implementation of the Java Persistence API (JPA) to simplify database access: ORM (Object-Relational Mapping)

In JPA, entity classes represent tables in the database, and relationships between entities are mapped using annotations.

1 JPA Implementations: ORM

OpenJPA, Hibernate, and EclipseLink are all popular ORM (Object-Relational Mapping) frameworks that provide implementations of the Java Persistence API (JPA).

These frameworks simplify database access and management by mapping Java objects to database tables, and they provide features to optimize database performance and reduce the amount of boilerplate code required to interact with the database.

OpenJPA is an Apache project that provides a lightweight, high-performance implementation of JPA.
Hibernate is a popular ORM framework that’s widely used in Spring Boot applications. It provides a rich set of features and has excellent community support.
EclipseLink is an open-source JPA implementation that’s known for its performance and flexibility, and it’s frequently used in Java EE applications.

2 ORM: Hibernate

Hibernate is a popular ORM (Object-Relational Mapping) framework that provides a powerful implementation of JPA. It’s widely used in Spring Boot applications to simplify database access and management.

Hibernate uses annotations and XML configurations to map Java objects to database tables, and it provides several features to simplify CRUD (Create, Read, Update, and Delete) operations on the database.

Hibernate also provides support for caching, lazy loading, and transaction management, which can help you optimize the performance of your application.

Spring Boot and Hibernate provide a powerful combination of tools for building Java-based web applications that interact with databases.

By using these frameworks together, you can simplify database access, improve performance, and focus on building the core functionality of your application.

When you use Hibernate in your Spring Boot application, you can define entity classes using JPA annotations, just like you would with the standard JPA implementation provided by Spring Boot. Hibernate also provides its own set of annotations that can be used to fine-tune the behavior of the ORM framework.

For example, you can use the @GeneratedValue annotation to specify how primary keys are generated, or the @Fetch annotation to specify how data is retrieved from the database.

In addition to its rich set of features, Hibernate is also known for its excellent documentation and community support. You can find plenty of tutorials, sample code, and forums online to help you get started with Hibernate in your Spring Boot application.

3 Annotations

JPA Annotations
Annotation	Description
@Entity	Specifies that the class is an entity and will be managed by the EntityManager.
@Table	Specifies the database table name for the entity.
@Id	Specifies the primary key field of the entity.
@GeneratedValue	Specifies how the primary key should be generated.
@Column	Specifies the database column name for a field.
@JoinColumn	Specifies the join column when using a relationship.
@OneToMany	Defines a one-to-many relationship between two entities.
@ManyToOne	Defines a many-to-one relationship between two entities.
@ManyToMany	Defines a many-to-many relationship between two entities.
@JoinTable	Specifies the join table for a many-to-many relationship.
@Embedded	Specifies that the field should be mapped as an embedded object.
@Transient	Specifies that the field should not be persisted to the database.

4 Relationships

Here are some of the most common JPA mappings and relationships used in Spring Boot

4.1 `@OneToMany`

@OneToMany: This annotation is used to represent a one-to-many relationship between two entities.

For example, if a customer can have multiple orders, you can define a @OneToMany relationship between the Customer entity and the Order entity.

Example:

API Rest Author-Book @OneToMany CRUD with Swagger

4.2 `@ManyToOne`

@ManyToOne: This annotation is used to represent a many-to-one relationship between two entities.

For example, if an order belongs to a customer, you can define a @ManyToOne relationship between the Order entity and the Customer entity.

Example:

Library-Book @ManyToMany and @OneToOne CRUD

4.3 `@ManyToMany`

@ManyToMany: This annotation is used to represent a many-to-many relationship between two entities.

For example, if a book can have multiple authors and an author can have written multiple books, you can define a @ManyToMany relationship between the Book entity and the Author entity.

Example:

API Rest Library-Book-Author @ManyToMany @OneToMany CRUD with Swagger and Inherence