Spring boot: JPA: @MappedSuperclass : Inherit properties from a super class

Using MappedSuperclass annotation, we can allow an entity to inherit the properties from a super class.

For example, in a typical application, we maintain below properties in every table.

a.   createdBy

b.   updatedBy

c.    createdTime

d.   updatedTime

Instead of putting all these properties in every entity, we can place these properties in a base entity (annotate base entity with MappedSuperclass annotation).

Example

@MappedSuperclass
public abstract class BaseEntity {
 @Column(name = "CREATED_BY", updatable = false)
 private String createdBy;

 @CreationTimestamp
 @Column(name = "CREATED_TIME", updatable = false)
 private Timestamp createdTime;

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

 @UpdateTimestamp
 @Column(name = "UPDATED_TIME")
 private Timestamp updatedTime;

 ......
 ......
}

@Entity
@Table(name = "employees")
public class Employee extends BaseEntity {

 @Id
 @GeneratedValue
 @Column(name = "EMPLOYEE_ID")
 private int id;

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

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

 ......
 ......
}

Find the complete working application.

BaseEntity.java    

package com.sample.app.entity;

import java.sql.Timestamp;

import javax.persistence.Column;
import javax.persistence.MappedSuperclass;

import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;

@MappedSuperclass
public abstract class BaseEntity {
 @Column(name = "CREATED_BY", updatable = false)
 private String createdBy;

 @CreationTimestamp
 @Column(name = "CREATED_TIME", updatable = false)
 private Timestamp createdTime;

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

 @UpdateTimestamp
 @Column(name = "UPDATED_TIME")
 private Timestamp updatedTime;

 public String getCreatedBy() {
  return createdBy;
 }

 public void setCreatedBy(String createdBy) {
  this.createdBy = createdBy;
 }

 public Timestamp getCreatedTime() {
  return createdTime;
 }

 public void setCreatedTime(Timestamp createdTime) {
  this.createdTime = createdTime;
 }

 public String getUpdatedBy() {
  return updatedBy;
 }

 public void setUpdatedBy(String updatedBy) {
  this.updatedBy = updatedBy;
 }

 public Timestamp getUpdatedTime() {
  return updatedTime;
 }

 public void setUpdatedTime(Timestamp updatedTime) {
  this.updatedTime = updatedTime;
 }

}

Employee.java

package com.sample.app.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "employees")
public class Employee extends BaseEntity {

 @Id
 @GeneratedValue
 @Column(name = "EMPLOYEE_ID")
 private int id;

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

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

 public int getId() {
  return id;
 }

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

 public String getFirstName() {
  return firstName;
 }

 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }

 public String getLastName() {
  return lastName;
 }

 public void setLastName(String lastName) {
  this.lastName = lastName;
 }

 @Override
 public String toString() {
  return "Employee [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", getCreatedBy()="
    + getCreatedBy() + ", getCreatedTime()=" + getCreatedTime() + ", getUpdatedBy()=" + getUpdatedBy()
    + ", getUpdatedTime()=" + getUpdatedTime() + "]";
 }

}

EmployeeRepository.java

package com.sample.app.repository;

import org.springframework.data.jpa.repository.JpaRepository;

import com.sample.app.entity.Employee;

public interface EmployeeRepository extends JpaRepository<Employee, Integer>{

}

App.java

package com.sample.app;

import java.util.Arrays;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import com.sample.app.entity.Employee;
import com.sample.app.repository.EmployeeRepository;

@SpringBootApplication
public class App {
 public static void main(String args[]) {
  SpringApplication.run(App.class, args);
 }

 @Bean
 public CommandLineRunner demo(EmployeeRepository empRepo) {
  return (args) -> {
   Employee emp1 = new Employee();
   Employee emp2 = new Employee();
   Employee emp3 = new Employee();

   emp1.setFirstName("Ram");
   emp1.setLastName("Majety");
   emp1.setCreatedBy("Ram");
   emp1.setUpdatedBy("Ram");

   emp2.setFirstName("Sowmya");
   emp2.setLastName("Konagandla");
   emp2.setCreatedBy("Ram");
   emp2.setUpdatedBy("Ram");

   emp3.setFirstName("Narendra");
   emp3.setLastName("Bora");
   emp3.setCreatedBy("Ram");
   emp3.setUpdatedBy("Ram");

   empRepo.saveAll(Arrays.asList(emp1, emp2, emp3));

   empRepo.findAll().forEach(System.out::println);

  };
 }

}

application.properties

logging.level.root=WARN
logging.level.org.hibernate=ERROR

## H2 specific properties
spring.h2.console.enabled=true
spring.h2.console.path=/h2

spring.datasource.url=jdbc:h2:file:~/db/myOrg.db;DB_CLOSE_ON_EXIT=FALSE;DB_CLOSE_DELAY=-1;

spring.datasource.username=krishna
spring.datasource.password=password123

spring.datasource.driverClassName=org.h2.Driver

## JPA specific properties
# Creates the schema, destroying previous data.
spring.jpa.hibernate.ddl-auto=create

spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

spring.jpa.show-sql=false
spring.jpa.properties.hibernate.format_sql=false

## Database connection pooling properties
# Number of ms to wait before throwing an exception if no connection is available.
spring.datasource.max-wait=10000

# Maximum number of active connections that can be allocated from this pool at the same time.
spring.datasource.tomcat.max-active=10
spring.datasource.tomcat.max-idle=5
spring.datasource.tomcat.min-idle=3

pom.xml

<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>springH2</groupId>
 <artifactId>springH2</artifactId>
 <version>1</version>

 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.1.6.RELEASE</version>
 </parent>

 <properties>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 </properties>

 <dependencies>

  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-data-jpa</artifactId>
  </dependency>

  <dependency>
   <groupId>com.h2database</groupId>
   <artifactId>h2</artifactId>
  </dependency>
  
 </dependencies>

</project>

Total project structure looks like below.

Run App.java, you can see below messages in console.

Employee [id=1, firstName=Ram, lastName=Majety, getCreatedBy()=Ram, getCreatedTime()=2019-09-28 22:12:28.484, getUpdatedBy()=Ram, getUpdatedTime()=2019-09-28 22:12:28.484]
Employee [id=2, firstName=Sowmya, lastName=Konagandla, getCreatedBy()=Ram, getCreatedTime()=2019-09-28 22:12:28.488, getUpdatedBy()=Ram, getUpdatedTime()=2019-09-28 22:12:28.488]
Employee [id=3, firstName=Narendra, lastName=Bora, getCreatedBy()=Ram, getCreatedTime()=2019-09-28 22:12:28.488, getUpdatedBy()=Ram, getUpdatedTime()=2019-09-28 22:12:28.488]

You can download complete working application from this link.

    

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