Spring Boot notes1 - Database and CURD

This notes is the learning process of Spring boot. Follow the https://www.udemy.com/course/spring-hibernate-tutorial/learn/lecture/12940996#overview

Connect to database

in the Resource path, there are a application.properties

input the JDBC properties

#
# JDBC properties

spring.datasource.url=jdbc:mysql://localhost:3306/employee_directory?useSSL=false&serverTimezone=UTC
spring.datasource.username=<username>
spring.datasource.password=<assword>

Create Entity

@Entity
@Table(name="employee")
public class Employee {

    // define fields

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

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

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

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


    // define constructors

    public Employee() {

    }

    public Employee(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    //define getter setter toString...
}

Hibernate implementation

Create a interface in src/java/projectname/dao/EmployeeDAO

DAO aka Data Access Object, is the “model” of MVC.

public interface EmployeeDAO {

    public List<Employee> findAll();

    public Employee findById(int theId);

    public void save(Employee theEmployee);

    public void delete(Employee theEmployee);

}

Implementing the interface in src/java/projectname/dao/EmployeeDAOHibernateImpl

@Repository

contains the api to control the database;
-. createQuery(…)

• .get(…)
• etc…

@Transactional

transaction is atom unit of the DBMS, Provides a way for database operation sequences to recover from failure to a normal state.
DBMS needs to ensure that all operations in the transaction are completed successfully and the results are permanently stored in the database.
IF some operations in the transaction are not completed successfully, all operations in the transaction need to be rolled back to the state before the transaction has no effect on the database or the execution of other transactions, and all transactions needs to be executed independently.

// repository contains the api to control the database;
@Repository
public class EmployeeDAOHibernateImpl implements EmployeeDAO {

    // define field for entitymanager
    private EntityManager entityManager;

    // set up constructor injection
    @Autowired
    public EmployeeDAOHibernateImpl(EntityManager theEntityManager) {
        entityManager = theEntityManager;
    }


    @Override
    @Transactional
    public List<Employee> findAll() {

        // get the current hibernate session
        Session currentSession = entityManager.unwrap(Session.class);

        // create a query
        Query<Employee> theQuery =
                currentSession.createQuery("select e from Employee e", Employee.class);

        // execute query and get result list
        List<Employee> employees = theQuery.getResultList();

        // return the results
        return employees;
    }

    @Override
    public Employee findById(int theId) {
        Session currentSession = entityManager.unwrap(Session.class);

        Employee theEmployee = currentSession.get(Employee.class, theId);
        return theEmployee;
    }

    @Override
    public void save(Employee theEmployee) {
        Session currentSession = entityManager.unwrap(Session.class);

        currentSession.saveOrUpdate(theEmployee);
    }

    @Override
    public void delete(Employee theEmployee) {
        Session currentSession = entityManager.unwrap(Session.class);

        currentSession.delete(theEmployee);
    }

}

Service

Mostly similar to the dao, first create a interface, then implementing the interface.

public interface EmployeeService {

    public List<Employee> findAll();

    public Employee findById(int theId);

    public void save(Employee theEmployee);

    public void deleteById( int theId);
}

@Service
public class EmployeeServiceImpl implements EmployeeService {
...
}

Rest

@RestController
@RequestMapping("/api")
public class EmployeeRestController {
    private EmployeeService employeeService;

    @Autowired
    public EmployeeRestController(EmployeeService theEmployeeService) {
        employeeService = theEmployeeService;
    }

    @GetMapping("/employees")...
    @PostMapping("/employees")...
    @GetMapping("/employees/{employeeId}")
    @PutMapping("/employees")
    @DeleteMapping("/employees/{employeeId}")
    ...
}