Persistenz

package at.aydin.lab.persistence.legacy;

import java.util.List;

// Design Pattern: DAO
// Zweck: SQL und JDBC werden hinter einer fachlichen Schnittstelle gekapselt.
public interface CustomerDao {
    Customer save(String name, String email);
    List<Customer> findAll();
}

package at.aydin.lab.persistence.legacy;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public final class JdbcCustomerDao implements CustomerDao {
    private final String url;

    public JdbcCustomerDao(String url) {
        this.url = url;
        initialize();
    }

    private Connection connection() throws SQLException {
        return DriverManager.getConnection(url, "sa", "");
    }

    private void initialize() {
        String sql = "create table if not exists customer("
                + "id bigint generated by default as identity primary key, "
                + "name varchar(120), email varchar(180))";

        try (Connection connection = connection();
                Statement statement = connection.createStatement()) {
            statement.executeUpdate(sql);
        } catch (SQLException exception) {
            throw new IllegalStateException("Schema konnte nicht erstellt werden", exception);
        }
    }

    @Override
    public Customer save(String name, String email) {
        String sql = "insert into customer(name,email) values (?,?)";
        try (Connection connection = connection();
                PreparedStatement statement = connection.prepareStatement(
                        sql, Statement.RETURN_GENERATED_KEYS)) {
            statement.setString(1, name);
            statement.setString(2, email);
            statement.executeUpdate();

            try (ResultSet keys = statement.getGeneratedKeys()) {
                if (!keys.next()) {
                    throw new SQLException("Keine ID erhalten");
                }
                return new Customer(keys.getLong(1), name, email);
            }
        } catch (SQLException exception) {
            throw new IllegalStateException("Kunde konnte nicht gespeichert werden", exception);
        }
    }

    @Override
    public List<Customer> findAll() {
        List<Customer> result = new ArrayList<>();
        String sql = "select id,name,email from customer order by id";

        try (Connection connection = connection();
                Statement statement = connection.createStatement();
                ResultSet resultSet = statement.executeQuery(sql)) {
            while (resultSet.next()) {
                result.add(new Customer(
                        resultSet.getLong("id"),
                        resultSet.getString("name"),
                        resultSet.getString("email")));
            }
            return result;
        } catch (SQLException exception) {
            throw new IllegalStateException("Kunden konnten nicht gelesen werden", exception);
        }
    }
}

package at.aydin.lab.persistence.modern;

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

// Design Pattern: Repository
// Zweck: Spring Data erzeugt die technische Implementierung aus dem Interface.
public interface CustomerRepository extends JpaRepository<CustomerEntity, Long> {
}

package at.aydin.lab.persistence.legacy;

public record Customer(long id, String name, String email) {
}

package at.aydin.lab.persistence.modern;

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.Table;

@Entity
@Table(name = "customer")
public class CustomerEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
    protected CustomerEntity() {
    }

    public CustomerEntity(String name, String email) {
        this.name = name;
        this.email = email;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }

    @Override
    public String toString() {
        return "CustomerEntity[id=" + id + ", name=" + name + ", email=" + email + "]";
    }
}

package at.aydin.lab.persistence.legacy;

public final class PersistenceLegacyApplication {
    private PersistenceLegacyApplication() {
    }

    public static void main(String[] args) {
        CustomerDao dao = new JdbcCustomerDao("jdbc:h2:mem:legacy;DB_CLOSE_DELAY=-1");
        dao.save("Aydin Polat", "aydin@example.test");
        dao.findAll().forEach(System.out::println);
    }
}

package at.aydin.lab.persistence.modern;

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

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

    @Bean
    CommandLineRunner demo(CustomerService service) {
        return args -> {
            service.create("Aydin Polat", "aydin@example.test");
            service.findAll().forEach(System.out::println);
        };
    }
}

package at.aydin.lab.persistence.modern;

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import java.util.List;

@Service
// Design Pattern: Service Layer
// Zweck: Transaktions- und Fachgrenze über dem Repository.
public class CustomerService {
    private final CustomerRepository repository;
    public CustomerService(CustomerRepository repository) {
        this.repository = repository;
    }

    @Transactional
    public CustomerEntity create(String name, String email) {
        return repository.save(new CustomerEntity(name, email));
    }

    @Transactional(readOnly = true)
    public List<CustomerEntity> findAll() {
        return repository.findAll();
    }
}