SpringBoot JPA @OneToMany Mapping : Fetch data from tables

SpringBoot JPA @OneToMany Mapping as name says we will see one to many mapping in SpringBoot and JPA.

First see the ER Diagram

SpringBoot JPA @OneToMany Mapping ER Diagram

Following is the Entity Relationship Diagram for user, user_mails and user_mobiles table.

One user can have multiple mail ids.

So this is a one to many relation.

similarly one user can have multiple mobile numbers.

This is also one to many mapping.

user’s id in user table is

Tools/Technology used

Spring Boot 2.2
JPA
Eclipse IDE
MySQL Database

SpringBoot JPA @OneToMany Mapping Directory Structure

SpringBoot JPA @OneToMany Mapping Project Directory Structure — Fig: Project Directory Structure

To build project we used maven and included

spring-boot-starter-web
spring-boot-starter-data-jpa
mysql-connector-java

You can also use spring Initializr to generate POM.xml

POM.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.7.2</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.ebhor</groupId>
	<artifactId>mvc</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>
	<name>Spring Crud</name>
	<description>Spring CRUD Example</description>
	<properties>
		<java.version>1.8</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jpa</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-tomcat</artifactId>
			<scope>provided</scope>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<scope>runtime</scope>
		</dependency>
		
	</dependencies>
	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>
</project>

<?xml version="1.0" encoding="UTF-8"?>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-parent</artifactId>

</parent>

<groupId>com.ebhor</groupId>

<version>0.0.1-SNAPSHOT</version>

<name>Spring Crud</name>

<description>Spring CRUD Example</description>

<java.version>1.8</java.version>

</properties>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-web</artifactId>

</dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-data-jpa</artifactId>

</dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-tomcat</artifactId>

<scope>provided</scope>

</dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-test</artifactId>

</dependency>

<groupId>mysql</groupId>

<artifactId>mysql-connector-java</artifactId>

<scope>runtime</scope>

</dependency>

</dependencies>

<build>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-maven-plugin</artifactId>

</plugin>

</plugins>

</build>

</project>

Application.properties file configuration

MySQL database is used.

Configuration with MySQL is as specified below

spring.datasource.url=jdbc:mysql://localhost:3306/ebhor
spring.datasource.username=root
spring.datasource.password=
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.jpa.hibernate.ddl-auto=update
spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

spring.datasource.url=jdbc:mysql://localhost:3306/ebhor

spring.datasource.username=root

spring.datasource.password=

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

spring.jpa.hibernate.ddl-auto=update

spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect

Entities

We have created three entity files User, UserMail and UserMobile.

Tables and columns are mapped in entity file.

User.java

To access multiple mail and mobile numbers user is mapped with UserMail and UserMobile entities.

@OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY) private Set userMails = new HashSet(0);

@OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY) private Set userMobiles = new HashSet(0);

@oneToMany mapping is used and few parameters are also used.

mappedBy- a property name in userMails. Based on this property matching oneToMany mapping will be performed.
cascade- Transactions that are performing on table will also perform on mapped table or not.
fetch – specifies when to access mapped data from join table

package com.ebhor.crud.entity;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Transient;
@Entity
@Table(name = "user")
public class User {
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	@Column(name = "id")
	private int id;
	@Column(name = "name", nullable = false)
	private String name;
	@OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
	private Set<UserMail> userMails = new HashSet<UserMail>(0);
	@OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
	private Set<UserMobile> userMobiles = new HashSet<UserMobile>(0);
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Set<UserMail> getUserMails() {
		return userMails;
	}
	public void setUserMails(Set<UserMail> userMails) {
		this.userMails = userMails;
	}
	public User(int id, String name, Set<UserMail> userMails) {
		super();
		this.id = id;
		this.name = name;
		this.userMails = userMails;
	}
	public User() {
		super();
	}
	public Set<UserMobile> getUserMobiles() {
		return userMobiles;
	}
	public void setUserMobiles(Set<UserMobile> userMobiles) {
		this.userMobiles = userMobiles;
	}
}

package com.ebhor.crud.entity;

import java.util.HashSet;

import java.util.Set;

import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.OneToMany;

import javax.persistence.Table;

import javax.persistence.Transient;

@Entity

@Table(name = "user")

public class User {

@Id

@GeneratedValue(strategy = GenerationType.AUTO)

@Column(name = "id")

private int id;

@Column(name = "name", nullable = false)

private String name;

@OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)

private Set<UserMail> userMails = new HashSet<UserMail>(0);

@OneToMany(mappedBy = "user", cascade = CascadeType.ALL, fetch = FetchType.LAZY)

private Set<UserMobile> userMobiles = new HashSet<UserMobile>(0);

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public Set<UserMail> getUserMails() {

return userMails;

}

public void setUserMails(Set<UserMail> userMails) {

this.userMails = userMails;

}

public User(int id, String name, Set<UserMail> userMails) {

super();

this.id = id;

this.name = name;

this.userMails = userMails;

}

public User() {

super();

}

public Set<UserMobile> getUserMobiles() {

return userMobiles;

}

public void setUserMobiles(Set<UserMobile> userMobiles) {

this.userMobiles = userMobiles;

}

UserMail.java

@ManyToOne(fetch = FetchType.LAZY, optional = false) @JoinColumn(name = "user_id") @JsonIgnore private User user;

Here User Object is mapped as Many to one.

The @JoinColumn specified based on which (user_mail) column it will perform join and fetch data.

@JsonIgnore- This will ignored the json result and prevent the loop.

package com.ebhor.crud.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import com.fasterxml.jackson.annotation.JsonIgnore;

@Entity
@Table(name = "user_mails")
public class UserMail {
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private int id;

	@Column(name = "email", nullable = false)
	private String email;

	@ManyToOne(fetch = FetchType.LAZY, optional = false)
	@JoinColumn(name = "user_id")
	@JsonIgnore
	private User user;

	public UserMail() {
		super();
	}

	public UserMail(int id, String email, User user) {
		super();
		this.id = id;
		this.email = email;
		this.user = user;
	}

	public int getId() {
		return id;
	}

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

	public String getEmail() {
		return email;
	}

	public void setEmail(String email) {
		this.email = email;
	}

	public User getUser() {
		return user;
	}

	public void setUser(User user) {
		this.user = user;
	}

}

package com.ebhor.crud.entity;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

import com.fasterxml.jackson.annotation.JsonIgnore;

@Entity

@Table(name = "user_mails")

public class UserMail {

@Id

@GeneratedValue(strategy = GenerationType.AUTO)

private int id;

@Column(name = "email", nullable = false)

private String email;

@ManyToOne(fetch = FetchType.LAZY, optional = false)

@JoinColumn(name = "user_id")

@JsonIgnore

private User user;

public UserMail() {

super();

}

public UserMail(int id, String email, User user) {

super();

this.id = id;

this.email = email;

this.user = user;

}

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getEmail() {

return email;

}

public void setEmail(String email) {

this.email = email;

}

public User getUser() {

return user;

}

public void setUser(User user) {

this.user = user;

}

UserMobiles

package com.ebhor.crud.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

import com.fasterxml.jackson.annotation.JsonIgnore;

@Entity
@Table(name = "user_mobiles")
public class UserMobile {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private int id;

	@Column(name = "mobile_no", nullable = false)
	private String mobileNo;

	@ManyToOne(fetch = FetchType.LAZY, optional = false)
	@JoinColumn(name = "user_id")
	@JsonIgnore
	private User user;

	public UserMobile() {

	}

	public UserMobile(int id, String mobileNo, User user) {
		super();
		this.id = id;
		this.mobileNo = mobileNo;
		this.user = user;
	}

	public int getId() {
		return id;
	}

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

	public String getMobileNo() {
		return mobileNo;
	}

	public void setMobileNo(String mobileNo) {
		this.mobileNo = mobileNo;
	}

	public User getUser() {
		return user;
	}

	public void setUser(User user) {
		this.user = user;
	}

}

package com.ebhor.crud.entity;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

import com.fasterxml.jackson.annotation.JsonIgnore;

@Entity

@Table(name = "user_mobiles")

public class UserMobile {

@Id

@GeneratedValue(strategy = GenerationType.AUTO)

private int id;

@Column(name = "mobile_no", nullable = false)

private String mobileNo;

@ManyToOne(fetch = FetchType.LAZY, optional = false)

@JoinColumn(name = "user_id")

@JsonIgnore

private User user;

public UserMobile() {

}

public UserMobile(int id, String mobileNo, User user) {

super();

this.id = id;

this.mobileNo = mobileNo;

this.user = user;

}

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getMobileNo() {

return mobileNo;

}

public void setMobileNo(String mobileNo) {

this.mobileNo = mobileNo;

}

public User getUser() {

return user;

}

public void setUser(User user) {

this.user = user;

}

UserDAO.java

UserDAO is responsible for fetching data from database.

package com.ebhor.crud.dao;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;
import com.ebhor.crud.entity.User;
@Repository
public interface UserDAO extends CrudRepository<User, Integer>{
}

package com.ebhor.crud.dao;

import org.springframework.data.repository.CrudRepository;

import org.springframework.stereotype.Repository;

import com.ebhor.crud.entity.User;

@Repository

public interface UserDAO extends CrudRepository<User, Integer>{

}

UserService.java

package com.ebhor.crud.service;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.ebhor.crud.dao.UserDAO;
import com.ebhor.crud.entity.User;
@Service
public class UserService {
	@Autowired
	UserDAO dao;
	public Iterable<User> getUsers(){
		return dao.findAll();
	}
}

package com.ebhor.crud.service;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.stereotype.Service;

import com.ebhor.crud.dao.UserDAO;

import com.ebhor.crud.entity.User;

@Service

public class UserService {

@Autowired

UserDAO dao;

public Iterable<User> getUsers(){

return dao.findAll();

}

UserController.java

Here we have used RestController to show data on index position

package com.ebhor.crud.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import com.ebhor.crud.entity.User;
import com.ebhor.crud.service.UserService;
@RestController
public class UserController {
	@Autowired
	UserService service;
	
	@GetMapping("/")
	public Iterable<User> users(){
		return service.getUsers();
	}
}

package com.ebhor.crud.controller;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.RestController;

import com.ebhor.crud.entity.User;

import com.ebhor.crud.service.UserService;

@RestController

public class UserController {

@Autowired

UserService service;

@GetMapping("/")

public Iterable<User> users(){

return service.getUsers();

}

Result

On running above project we will get following data.

Angular Spring Boot Showing Data In Table