[Spring] Spring REST Data JPA

Application Architecture

REST CRUD APIs(9)

The Problem

• We saw how to create a DAO of Employee
• What if we need to create a DAO for another entity?
  • Customer, Student, Product, Book…
• Do we have to repeat all of the same code again?

Creating DAO

• You may have noticed a pattern with creating DAOs

Wish

• Create a DAO for me
• Plug in my entity type and primary key
• Give me all of the basic CRUD features for free

Spring Data JPA - Solution

• Spring Data JPA is the solution!! – https://spring.io/projects/spring-data-jpa
• Create a DAO and just plug in your entity type and primary key
• Spring will give you a CRUD implementation for FREE
  • Helps to minimize boiler-plate DAO code

    More than 70% reduction in code .. depending on use case

JpaRepository

• Spring Data JPA provides the interface: JpaRepository
• Expose methods (some by inheritance from parents)

Development Process

1. Extend JpaRepository interface
2. Use your Repository in your app

   No need for implementation class

Step 1: Extend JpaRepository interface

public interface EmployeeRepository extends JpaRepository<Employee//(Entity type)
, Integer//(primary key)> {
>{
	that's it ... no deed to write any code
	No need for implementation class
}

JpaRepository Docs

• Full list of methods available … see JavaDoc for JpaRepository https://docs.spring.io/spring-data/jpa/docs/current/api/org/springframework/data/jpa/repository/JpaRepository.html

Step 2: Use Repository in your app

@Service
public class EmployeeServiceImpl implements EmployeeService {

	private EmployeeRepository employeeRepository

	@Autowired
	public EmployeeServiceImpl (EmployeeRepository theEmployeeRepository) {
		employeeRepository = theEmployeeRepository;
	}

	@Override
	public List<Employee> findAll() {
		return employeeRepository.findAll(); <- Magic method that is available via repository
	}
}

Minimized Boilerplate Code

• Before Spring Data JPA
  • We’d create our Interface for given entity
  • We’d write our repository or our DAO implementation

    2 Files , 30+ lines of code

• After Spring Data JPA
  • We create this interface employee repository

    • 1 File, 3 lines of code!
    • No need for implementation class

Advanced Features

• Advanced features available for
  • Extending and adding custom queries with JPQL
  • Query Domain Specific Language (Query DSL)
  • Defining custom methods (low-level coding)

Refactor

package com.luv2code.springboot.cruddemo.service;  
  
import com.luv2code.springboot.cruddemo.dao.EmployeeRepository;  
import com.luv2code.springboot.cruddemo.entity.Employee;  
import jakarta.transaction.Transactional;  
import org.springframework.beans.factory.annotation.Autowired;  
import org.springframework.stereotype.Service;  
  
import java.util.List;  
import java.util.Optional;  
  
@Service  
public class EmployeeServiceImpl implements EmployeeService {  
  
    private EmployeeRepository employeeRepository;  
  
    @Autowired  
    public EmployeeServiceImpl (EmployeeRepository theEmployeeRepository) {  
        employeeRepository = theEmployeeRepository;  
    }  
    @Override  
    public List<Employee> findAll() {  
        return employeeRepository.findAll();  
    }  
  
    @Override  
    public Employee findById(int theId) {  
        Optional<Employee> result = employeeRepository.findById(theId);  
  
        Employee theEmployee = null;  
  
        if (result.isPresent()) {  
            theEmployee = result.get();  
        }  
        else {  
            // we didn't find the employee  
            throw new RuntimeException ("Did not find employee id - " + theId);  
        }  
        return theEmployee;  
    }  
  
    //@Transactional  
    @Override  
    public Employee save(Employee theEmployee) {  
        return employeeRepository.save(theEmployee);  
    }  
  
    //@Transactional  
    @Override  
    public void deleteById(int theId) {  
        employeeRepository.deleteById(theId);  
    }  
}

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