Java ORM 选型困局：JPA 的优雅幻觉与 xbatis 的破局思路

@Entity
@Table(name = "t_order")
public class Order {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String orderNo;
    private BigDecimal amount;
    private LocalDateTime createdAt;
    // getter/setter 略
}

// 单表查询确实简单
Order order = entityManager.find(Order.class, 1L);
List<Order> orders = orderRepository.findByAmountGreaterThan(BigDecimal.valueOf(100));

// 复杂动态查询——JPQL 写起来并不比 SQL 简单
@Query("SELECT o FROM Order o " +
       "JOIN o.customer c " +
       "JOIN o.items i " +
       "WHERE c.level >= :level " +
       "AND o.amount BETWEEN :min AND :max " +
       "AND i.productType IN :types " +
       "ORDER BY o.createdAt DESC")
List<Order> findComplex(@Param("level") int level,
                        @Param("min") BigDecimal min,
                        @Param("max") BigDecimal max,
                        @Param("types") List<String> types);

// MyBatis-Plus 单表查询
List<Order> orders = orderMapper.selectList(
    new QueryWrapper<Order>()
        .gt("amount", 100)
        .orderByDesc("created_at")
);

// xbatis 动态多条件查询——类型安全，无 XML
List<Order> orders = xbatis.query(Order.class)
    .join(Customer.class, on -> on.eq(Order.customerId, Customer.id))
    .where(w -> w
        .gt(Customer.level, 3)
        .between(Order.amount, 100, 5000)
        .in(Order.status, List.of("PAID", "SHIPPED"))
    )
    .orderBy(Order.createdAt, Direction.DESC)
    .limit(20)
    .list();

// 生成的 SQL 可以直接打印检查
System.out.println(xbatis.lastSql()); 
// → SELECT o.*, c.* FROM t_order o 
//   JOIN t_customer c ON o.customer_id = c.id 
//   WHERE c.level > 3 AND o.amount BETWEEN 100 AND 5000 
//   AND o.status IN ('PAID','SHIPPED') 
//   ORDER BY o.created_at DESC LIMIT 20

<select id="findComplexOrders" resultType="Order">
    SELECT o.*, c.level AS customer_level
    FROM t_order o
    JOIN t_customer c ON o.customer_id = c.id
    <where>
        <if test="level != null">AND c.level > #{level}</if>
        <if test="min != null and max != null">
            AND o.amount BETWEEN #{min} AND #{max}
        </if>
        <if test="statuses != null and statuses.size() > 0">
            AND o.status IN
            <foreach collection="statuses" item="s" open="(" separator="," close=")">
                #{s}
            </foreach>
        </if>
    </where>
    ORDER BY o.created_at DESC
    LIMIT #{limit}
</select>

<!-- pom.xml 添加 xbatis 依赖 -->
<dependency>
    <groupId>com.xbatis</groupId>
    <artifactId>xbatis-core</artifactId>
    <version>1.x.x</version> <!-- 请替换为实际最新版本 -->
</dependency>

// 配置数据源（与 MyBatis-Plus 共用同一 DataSource 即可）
@Configuration
public class XbatisConfig {
    @Bean
    public XbatisSessionFactory sessionFactory(DataSource dataSource) {
        return XbatisSessionFactoryBuilder
            .create()
            .dataSource(dataSource)
            .scanPackages("com.yourcompany.entity")  // 实体类扫描路径
            .build();
    }
}

// 先在一个新查询上试水，不改动现有 MyBatis-Plus 代码
@Service
public class OrderQueryService {
    // 旧代码保留
    @Autowired private OrderMapper orderMapper;

    // 新查询用 xbatis
    @Autowired private XbatisSessionFactory sessionFactory;

    public List<Order> searchOrders(OrderSearchDTO dto) {
        return sessionFactory.query(Order.class)
            .where(w -> w
                .like(Order.orderNo, dto.getKeyword())   // 类型安全，字段名不会写错
                .eq(Order.status, dto.getStatus())
                .ge(Order.createdAt, dto.getStartDate())
            )
            .orderBy(Order.createdAt, Direction.DESC)
            .page(dto.getPageNum(), dto.getPageSize())
            .list();
    }
}