Mybatis-Plus - 条件构造器 QueryWrapper 的使用
目录
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;
/**
* 构造ProductWithItemsVo对象用于出参
* @param product
* @param 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;
}
/**
* wrapper.eq("banner_id", id)
* banner_id 数据库字段
* id 判断相等的值
*/
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<>();
/**
* lambda方法引用
*/
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：
/**
* 方式一
*/
LambdaQueryWrapper<ProductItem> wrapper1 = new QueryWrapper<ProductItem>().lambda();
wrapper1.eq(ProductItem::getProductId, id);
List<ProductItem> productItems1 = productItemMapper.selectList(wrapper1);
/**
* 方式二
*/
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;
}
/**
* 链式调用
*/
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
