假如我們有一張banner_item表，現(xiàn)需要通過banner_id查出所有數(shù)據(jù)(查詢List)

@Data
public class BannerItem {

    private Long id;

    private String name;

    private String img;

    private String keyword;

    private Integer type;

    private Long bannerId;
}

• QueryWrapper

最基礎(chǔ)的使用方式是這樣

// 查詢條件構(gòu)造器
QueryWrapper<BannerItem> wrapper = new QueryWrapper<>();
wrapper.eq("banner_id", id);
// 查詢操作
List<BannerItem> bannerItems = bannerItemMapper.selectList(wrapper);

然后我們可以引入lambda，避免我們在代碼中寫類似的于banner_id的硬編碼

QueryWrapper<BannerItem> wrapper = new QueryWrapper<>();
wrapper.lambda().eq(BannerItem::getBannerId, id);
List<BannerItem> bannerItems = bannerItemMapper.selectList(wrapper);

• LambdaQueryWrapper

為了簡化lambda的使用，我們可以改寫成LambdaQueryWrapper構(gòu)造器，語法如下：

LambdaQueryWrapper<BannerItem> wrapper = new QueryWrapper<BannerItem>().lambda();
wrapper.eq(BannerItem::getBannerId, id);
List<BannerItem> bannerItems = bannerItemMapper.selectList(wrapper);

我們可以再次將QueryWrapper<BannerItem>.lambda()簡化，變成這個樣子

LambdaQueryWrapper<BannerItem> wrapper = new LambdaQueryWrapper<>();
wrapper.eq(BannerItem::getBannerId, id);
List<BannerItem> bannerItems = bannerItemMapper.selectList(wrapper);

• 鏈?zhǔn)讲樵?/strong>

List<BannerItem> bannerItems = new LambdaQueryChainWrapper<>(bannerItemMapper)
                        .eq(BannerItem::getBannerId, id)
                        .list();

BannerItem bannerItem = new LambdaQueryChainWrapper<>(bannerItemMapper)
                        .eq(BannerItem::getId, id)
                        .one();