import com.querydsl.jpa.impl.JPAQueryFactory;
import jakarta.persistence.EntityManager;
import jakarta.persistence.LockModeType;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class ProductService {
    private final JPAQueryFactory queryFactory;

    public ProductService(EntityManager entityManager) {
        this.queryFactory = new JPAQueryFactory(entityManager);
    }

    @Transactional
    public Product findByIdWithLock(Long productId) {
        QProduct product = QProduct.product;

        // Pessimistic Write Lock 설정
        return queryFactory.selectFrom(product)
                .where(product.id.eq(productId))
                .setLockMode(LockModeType.PESSIMISTIC_WRITE)
                .fetchOne();
    }
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class DatabaseLockExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/your_database";
        String user = "your_username";
        String password = "your_password";

        try (Connection connection = DriverManager.getConnection(url, user, password)) {
            // Auto-commit 비활성화
            connection.setAutoCommit(false);

            // SELECT ... FOR UPDATE (행 잠금 설정)
            String sql = "SELECT * FROM your_table WHERE id = ? FOR UPDATE";
            try (PreparedStatement preparedStatement = connection.prepareStatement(sql)) {
                preparedStatement.setInt(1, 1); // ID 값 바인딩
                ResultSet resultSet = preparedStatement.executeQuery();

                while (resultSet.next()) {
                    System.out.println("Data: " + resultSet.getString("your_column"));
                }

                // 작업 후 커밋
                connection.commit();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class MemberService {
    private final MemberRepository memberRepository;

    public MemberService(MemberRepository memberRepository) {
        this.memberRepository = memberRepository;
    }

    @Transactional
    public void updateMember(Long id, String name) {
        Member member = memberRepository.findById(id)
                .orElseThrow(() -> new IllegalArgumentException("Member not found"));

        member.setName(name);  // JPA 영속성 컨텍스트에 의해 자동으로 업데이트됨
    }
}

import org.springframework.transaction.annotation.Transactional;

@Service
public class MemberService {

    @Transactional
    public void joinMember(Member member) {
        memberRepository.save(member);
        // 예외 발생 시 전체 트랜잭션 롤백
    }
}

@Transactional
@Service
public class MemberService {
    public void method1() {
        // 트랜잭션 적용됨
    }

    public void method2() {
        // 트랜잭션 적용됨
    }
}