前言
记录下Mybatis-Plus中条件构造器Wrapper 的一些基本用法。
查询示例
表结构
CREATE TABLE `product` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`title` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,
`create_time` datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=35 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci
CREATE TABLE `product_item` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`title` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,
`product_id` int(10) unsigned NOT NULL,
`create_time` datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci实现需求：
根据product - id查询product实例及其关联的product_item，如下:
基础代码
ProductController.java
@GetMapping("/{id}")
public ProductWithItemsVo getWithItems(@PathVariable Integer id) {
return productService.getWithItems(id);
}ProductService.java
public interface ProductService {
ProductWithItemsVo getWithItems(Integer id);
}ProductServiceImpl.java
@Service
public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product> implements ProductService {
@Autowired
private ProductItemMapper productItemMapper;
@Override
public ProductWithItemsVo getWithItems(Integer id) {
// 实现代码
}
}mapper
@Repository
public interface ProductMapper extends BaseMapper<Product> {
}
@Repository
public interface ProductItemMapper extends BaseMapper<ProductItem> {
}model
@Getter
@Setter
@TableName("product")
public class Product {
private Integer id;
private String title;
@JsonIgnore
private Date createTime;
}
@Getter
@Setter
@TableName("product_item")
public class ProductItem {
private Integer id;
private Integer productId;
private String title;
@JsonIgnore
private Date createTime;
}vo出参
@Data
@NoArgsConstructor
public class ProductWithItemsVo {
private Integer id;
private String title;
List<ProductItem> items;
public ProductWithItemsVo(Product product, List<ProductItem> items) {
BeanUtils.copyProperties(product, this);
this.setItems(items);
}
}QueryWrapper 的基本使用
@Override
public ProductWithItemsVo getWithItems(Integer id) {
Product product = this.getById(id);
if (Objects.isNull(product)) {
System.out.println("未查询到product");
return null;
}
QueryWrapper<ProductItem> wrapper = new QueryWrapper<>();
wrapper.eq("product_id", id);
List<ProductItem> productItems = productItemMapper.selectList(wrapper);
return new ProductWithItemsVo(product, productItems);
}如上代码，通过条件构造器QueryWrapper查询出当前product实例及其关联的product_item
QueryWrapper 的lambada写法
@Override
public ProductWithItemsVo getWithItems(Integer id) {
Product product = this.getById(id);
if (Objects.isNull(product)) {
System.out.println("未查询到product");
return null;
}
QueryWrapper<ProductItem> wrapper = new QueryWrapper<>();
wrapper.lambda().eq(ProductItem::getProductId, id);
List<ProductItem> productItems = productItemMapper.selectList(wrapper);
return new ProductWithItemsVo(product, productItems);
}如上代码，通过条件构造器QueryWrapper的lambda方法引用查询出当前product实例及其关联的product_item
LambadaQueryWrapper 的使用
LambadaQueryWrapper用于Lambda语法使用的QueryWrapper- 构建
LambadaQueryWrapper的方式：
LambdaQueryWrapper<ProductItem> wrapper1 = new QueryWrapper<ProductItem>().lambda();
wrapper1.eq(ProductItem::getProductId, id);
List<ProductItem> productItems1 = productItemMapper.selectList(wrapper1);
LambdaQueryWrapper<ProductItem> wrapper2 = new LambdaQueryWrapper<>();
wrapper2.eq(ProductItem::getProductId, id);
List<ProductItem> productItems2 = productItemMapper.selectList(wrapper2);完整代码
@Override
public ProductWithItemsVo getWithItems(Integer id) {
Product product = this.getById(id);
if (Objects.isNull(product)) {
System.out.println("未查询到product");
return null;
}
LambdaQueryWrapper<ProductItem> wrapper = new LambdaQueryWrapper<>();
wrapper.eq(ProductItem::getProductId, id);
List<ProductItem> productItems = productItemMapper.selectList(wrapper);
return new ProductWithItemsVo(product, productItems);
}如上代码，通过条件构造器LambdaQueryWrapper查询出当前product实例及其关联的product_item
LambdaQueryChainWrapper 的链式调用
@Override
public ProductWithItemsVo getWithItems(Integer id) {
Product product = this.getById(id);
if (Objects.isNull(product)) {
System.out.println("未查询到product");
return null;
}
List<ProductItem> productItems =
new LambdaQueryChainWrapper<>(productItemMapper)
.eq(ProductItem::getProductId, id)
.list();
return new ProductWithItemsVo(product, productItems);
}如上代码，通过链式调用查询出当前product实例及其关联的product_item
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