@OneToMany relationship in Spring Boot - Mini Project: Build & Apply

Create a @OneToMany Relationship in Spring Boot

📖 Scenario: You are building a simple Spring Boot application to manage a library. Each Author can write many Books. You need to set up the data model to reflect this relationship.

🎯 Goal: Build two Java entity classes, Author and Book, where one author can have many books using the @OneToMany annotation in Spring Boot.

📋 What You'll Learn

Create an Author entity class with an id and name field

Create a Book entity class with an id, title, and a reference to Author

Add a @OneToMany relationship in Author to hold multiple Book objects

Add a @ManyToOne relationship in Book to link back to Author

💡 Why This Matters

🌍 Real World

Managing related data in applications like libraries, stores, or blogs where one entity owns many related entities.

💼 Career

Understanding and implementing JPA relationships is essential for backend developers working with Spring Boot and databases.

1

Create the Author entity class

Create a Java class called Author annotated with @Entity. Add a private Long id field annotated with @Id and @GeneratedValue. Add a private String name field. Include standard getters and setters.

Spring Boot

// Your code here to create Author entity with id and name fields

Need a hint?

Use @Entity on the class. Use @Id and @GeneratedValue on the id field.

2

Create the Book entity class with author reference

Create a Java class called Book annotated with @Entity. Add a private Long id field annotated with @Id and @GeneratedValue. Add a private String title field. Add a private Author author field annotated with @ManyToOne. Include standard getters and setters.

Spring Boot

import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.ManyToOne;

// Your code here to create Book entity with id, title, and author fields

Need a hint?

Use @ManyToOne on the author field to link back to Author.

3

Add @OneToMany relationship in Author

In the Author class, add a private List<Book> books field annotated with @OneToMany(mappedBy = "author"). Initialize it with new ArrayList<>(). Add standard getter and setter for books. Import necessary classes.

Spring Boot

import java.util.List;
import java.util.ArrayList;
import jakarta.persistence.OneToMany;

// Your code here to add List books with @OneToMany(mappedBy = "author") in Author class

Need a hint?

Use @OneToMany(mappedBy = "author") on the books field. Initialize it with new ArrayList<>().

4

Complete the entity classes with imports and annotations

Ensure both Author and Book classes have all necessary imports for JPA annotations and collections. Confirm @Entity is present on both classes. Confirm @Id, @GeneratedValue, @OneToMany(mappedBy = "author"), and @ManyToOne annotations are correctly placed.

Spring Boot

// Review and add any missing imports or annotations to complete the entity classes

Need a hint?

Check that all imports and annotations are present and correctly placed in both classes.