MybatisPlus实现悲观锁 & 乐观锁的项目实践

@Data
public class Product {
    private Long id;
    private String name;
    private Integer price;
    
    @Version  // 乐观锁版本号字段
    private Integer version;
}

@Configuration
public class MybatisPlusConfig {
    
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // 添加乐观锁拦截器
        interceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor());
        return interceptor;
    }
}

// 1. 先查询出实体（version 会被查出来）
Product product = productService.getById(1L);

// 2. 修改数据
product.setPrice(product.getPrice() + 100);

// 3. 执行更新（MP 会自动在 WHERE 条件中加上 version = ?）
// 生成的 SQL 类似：
// UPDATE product SET price=?, version=version+1 WHERE id=? AND version=?
boolean success = productService.updateById(product);

// 批量更新时，每个实体的 version 都会参与 WHERE 条件
productService.updateBatchById(productList);

public interface ProductMapper extends BaseMapper<Product> {
    
    @Select("SELECT * FROM product WHERE id = #{id} FOR UPDATE")
    Product selectByIdForUpdate(Long id);
}

@Service
public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product> 
    implements ProductService {
    
    @Transactional  // 必须在事务中，FOR UPDATE 才有效
    public void deductStock(Long id) {
        // 1. 加锁查询
        Product product = baseMapper.selectByIdForUpdate(id);
        
        // 2. 执行业务逻辑
        if (product.getStock() > 0) {
            product.setStock(product.getStock() - 1);
            updateById(product);
        }
    }
}

<!-- ProductMapper.xml -->
<select id="selectByIdForUpdate" resultType="com.example.entity.Product">
    SELECT * FROM product WHERE id = #{id} FOR UPDATE
</select>

// 简单的重试机制
public boolean updateWithRetry(Product product, int maxRetries) {
    for (int i = 0; i < maxRetries; i++) {
        if (productService.updateById(product)) {
            return true;
        }
        // 重新查询最新数据
        product = productService.getById(product.getId());
    }
    throw new RuntimeException("更新失败，请重试");
}