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

Create a @ManyToOne Relationship in Spring Boot

📖 Scenario: You are building a simple Spring Boot application to manage books and their authors. Each book is written by one author, but an author can write many books.

🎯 Goal: Build two Java classes, Author and Book, where Book has a @ManyToOne relationship to Author. This means each book is linked to one author.

📋 What You'll Learn

Create an Author entity with id and name fields

Create a Book entity with id, title, and a @ManyToOne relationship to Author

Use proper JPA annotations for entity and relationship mapping

Include getters and setters for all fields

💡 Why This Matters

🌍 Real World

Managing data with relationships is common in apps like libraries, stores, or social media. This project shows how to link entities with @ManyToOne in Spring Boot.

💼 Career

Understanding JPA relationships is essential for backend developers working with databases in Java Spring Boot applications.

1

Create the Author entity

Create a Java class called Author annotated with @Entity. Add private fields Long id annotated with @Id and @GeneratedValue, and String name. Add public getters and setters for both fields.

Spring Boot

@Entity
public class Author {
    // Your code here
}

Need a hint?

Remember to import javax.persistence.Entity, javax.persistence.Id, and javax.persistence.GeneratedValue.

2

Create the Book entity with basic fields

Create a Java class called Book annotated with @Entity. Add private fields Long id annotated with @Id and @GeneratedValue, and String title. Add public getters and setters for both fields.

Spring Boot

@Entity
public class Book {
    // Your code here
}

Need a hint?

Use the same annotations as in the Author class for id.

3

Add the @ManyToOne relationship in Book

In the Book class, add a private field Author author annotated with @ManyToOne. Add public getter and setter for author.

Spring Boot

@Entity
public class Author {
    @Id
    @GeneratedValue
    private Long id;
    private String name;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

@Entity
public class Book {
    @Id
    @GeneratedValue
    private Long id;
    private String title;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    // Add the author field with @ManyToOne annotation below
    // Your code here
}

Need a hint?

Import javax.persistence.ManyToOne and add the field with getter and setter.

4

Complete the relationship with @JoinColumn

In the Book class, add @JoinColumn(name = "author_id") annotation above the author field to specify the foreign key column name.

Spring Boot

@Entity
public class Author {
    @Id
    @GeneratedValue
    private Long id;
    private String name;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

@Entity
public class Book {
    @Id
    @GeneratedValue
    private Long id;
    private String title;

    // Add @JoinColumn annotation above author field
    @ManyToOne
    private Author author;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Author getAuthor() {
        return author;
    }

    public void setAuthor(Author author) {
        this.author = author;
    }
}

Need a hint?

This annotation tells JPA the name of the foreign key column in the Book table.