🚀 Mastering Spring Data JPA: Implementing @OneToMany Mapping with User and MobilePhone Entities

In my previous guide, we explored @OneToOne mapping between User and AadharCard entities. Now, we’ll move on to @OneToMany mapping between User and MobilePhone entities in Spring Data JPA. This guide will show you how to efficiently manage one-to-many relationships in your Spring Boot applications.

Understanding @OneToMany Mapping

@OneToMany mapping with User and MobilePhone means one user can have multiple mobile phones associated with them. For example, a User entity may be associated with several MobilePhone entities, each representing a different mobile phone number or device owned by that user. This relationship allows for efficient management and retrieval of data related to a user's mobile phones within a Spring Boot application.

Prerequisites

Before we dive into the code, make sure you have:

• Set up your Spring Boot project with dependencies for Spring Data JPA.

• Defined your User and MobilePhone entities with appropriate annotations.

Implementing @OneToMany Mapping

To implement @OneToMany mapping in JPA, follow these steps:

Create User and MobilePhone entities with proper annotations to establish the relationship.

User.java

package com.Spring_Data_Jpa.Entity;

import jakarta.persistence.*;
import lombok.Data;
import java.util.List;

@Entity
@Data
@Table(name = "user")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private long ID;

    @Column(name = "name")
    private String name;

    @Column(name = "email")
    private String email;

    @OneToOne(cascade = CascadeType.ALL)
    private AadharCard aadharCard;

    @OneToMany(mappedBy = "user",cascade = CascadeType.ALL)
    private List<MobilePhone> mobilePhones;
}

MobilePhone.java

package com.Spring_Data_Jpa.Entity;

import jakarta.persistence.*;
import lombok.Data;

@Entity
@Data
@Table(name="mobile_phone")
public class MobilePhone {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private long id;

    @Column(name = "mobileNumber")
    private long mobileNumber;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;
}

Create a Repository interface for managing entities

MobilePhoneRepository

package com.Spring_Data_Jpa.Repository;

import com.Spring_Data_Jpa.Entity.MobilePhone;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface MobilePhoneRepository extends JpaRepository<MobilePhone,Long > {
}

Create a Controller class for handling requests related to User Entities

package com.Spring_Data_Jpa.Controller;

import com.Spring_Data_Jpa.Entity.AadharCard;
import com.Spring_Data_Jpa.Entity.MobilePhone;
import com.Spring_Data_Jpa.Entity.User;
import com.Spring_Data_Jpa.Repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
public class UserController {

    @Autowired
    UserRepository userRepository;

    @PostMapping("/addUser")
    public String addUser(@RequestBody User user, AadharCard aadharCard) {

        if (user.getAadharCard() != null) {
            aadharCard = user.getAadharCard();
            aadharCard.setUser(user); // Set the user in the AadharCard
        }

        // Saving Mobile Numbers
        if (user.getMobilePhones() != null) {
            for (MobilePhone mobilePhone : user.getMobilePhones()) {
                mobilePhone.setUser(user); // Set the user in each MobilePhone
            }
        }
        userRepository.save(user);
        return "User and AadharCard saved successfully!";
    }
}

Testing the @OneToMany Mapping with Postman

Add User: POST /addUser

{
    "name": "Mitchell S",
    "email": "smitchell@gmail.com",
    "aadharCard": {
        "number": 619910001617
    },
    "mobilePhones": [
        { "mobileNumber": 8987286451 },
        { "mobileNumber": 197382611 }
    ]
}

Conclusion:

We've implemented one-to-many mappings between the User and MobilePhone entities. It's similar to how you might have one AadharCard linked to a single person. However, with mobile phones, it's the opposite: one user can have many mobile phone numbers. Our database keeps track of which phones belong to each user thanks to a special user ID stored in each mobile phone record. This makes it easy to find all the mobile numbers associated with a particular user in your application.

GitHub Access:

You can access the code on GitHub here. Feel free to fork the repository and try it out yourself.

About Me:

LinkedIn | GitHub