需求：通过查看当前商品ID，也要有展示当前商品可以使用的优惠券。用Feign组件，传产品ID，调用优惠券的Service

前提：微服务项目中数据库表设计尽量都是单表查询，商品表和优惠券表联系用第三个表来联系

商品表设计：

优惠券表：

联系表：

 优惠券的业务：

@Service
public class CouponServiceImpl implements CouponService {
    @Resource
    CouponMapper couponMapper;
    @Resource
    CouponProductRelationMapper productRelationMapper;

    @Override
    public ResponseResult<List<CouponVo>> list(Long productId) {
        List<Coupon> couponList=new ArrayList<>();
        QueryWrapper<CouponProductRelation> relationQueryWrapper=new QueryWrapper<>();
        relationQueryWrapper.lambda().eq(CouponProductRelation::getProductId,productId);
        List<CouponProductRelation> relations = productRelationMapper.selectList(relationQueryWrapper);
        if (relations!=null&&relations.size()>0){
            for (CouponProductRelation c:
                    relations) {
                QueryWrapper<Coupon>queryWrapper=new QueryWrapper<>();
                queryWrapper.lambda().eq(Coupon::getId,c.getCouponId());
                Coupon coupon = couponMapper.selectOne(queryWrapper);
                couponList.add(coupon);
            }
            

        }
        List<CouponVo> voList = CommonBeanUtils.copyListProperties(couponList, CouponVo::new);

        return   ResponseResult.success(voList) ;
    }
}

Feign调用：

@FeignClient(value = "cloud-coupon",path = "/coupon")
public interface CouponFeignApi {
    @GetMapping("/list")
    ResponseResult<List<CouponVo>> list(@RequestParam Long id);
}

消费者：

商品调用

@Service
public class ProductServiceImpl implements ProductService {
    @Resource
    ProductMapper productMapper;
    @Resource
    ProductSpecsMapper productSpecsMapper;
    @Resource
    CouponFeignApi couponFeignApi;

    @Override
    public ResponseResult<ProductVo> detail(Long productId) {
        Product product = productMapper.selectId(productId);
        ProductVo productVo = new ProductVo();
        BeanUtils.copyProperties(product, productVo);
        List<ProductSpecsVo> productVos = CommonBeanUtils.copyListProperties(productSpecsMapper.selectByProductId(productId), ProductSpecsVo::new);
        productVo.setProductSpecsList(productVos);
        ResponseResult<List<CouponVo>> list = couponFeignApi.list(productId);
        List<CouponVo> data = list.getData();
        productVo.setCouponVoList(data);
        return ResponseResult.success(productVo);
    }
}