struts2之关联查询

Posted 2020-10-13 但为君故L

需要关联四个表

select g.*,b.name brname,s.bid,s.sname,bi.name biname  from T_GOODS g

left join T_brand b on b.id = g.brandid 

inner join T_smallclass s on g.sid = s.sid 

inner join T_bigclass bi on bi.id = s.bid"

T_GOODS   商品表格

 

商品实体类

 

public class Goods {
public int id;
public String goodsname;
public double weight;
public double price;
public String color;
public int brandid;
public Date shangtime;
public int stock;
public int sid;
public BigClass bigclass;  //其实是大分类与小分类的实体类，写一个了，不允许这样，因为主键不清
public Brand brand;//其实是把品牌实体类写在商品实体类，后台需要

}

 

 

T_brand     品牌表格

品牌实体类

public class Brand {
private int id;
private String name;

}

 

T_smallclass  小分类表格

 

public class SmallClass {
private int id;
private String name;
public int bid;

}

 

T_bigclass   大分类表格

public class BigClass {
//大分类
private int id;
private String name;

}

//商品关联查询
public List<Goods> goodslist();

 

//商品关联查询

connection = DBUtil.getConnection();
String sql = "select g.*,b.name brname,s.bid,s.sname,bi.name biname "
+ " from T_GOODS g left join T_brand b on b.id = g.brandid"
+ " inner join T_smallclass s on g.sid = s.sid"
+ " inner join T_bigclass bi on bi.id = s.bid";
p = connection.prepareStatement(sql);
set = p.executeQuery();
List<Goods> list = new ArrayList<Goods>();
while(set.next()){
Goods goods = new Goods();
goods.setId(set.getInt("id"));
goods.setGoodsname(set.getString("goodsname"));
// goods.setBrandid(set.getInt("brandid"));
goods.setColor(set.getString("color"));
goods.setPrice(set.getDouble("price"));
goods.setShangtime(set.getDate("shangtime"));
// goods.setSid(set.getInt("sid"));
goods.setStock(set.getInt("stock"));
goods.setWeight(set.getDouble("weight"));
goods.setBrand(new Brand());
goods.getBrand().setId(set.getInt("brandid"));
goods.getBrand().setName(set.getString("brname"));
goods.setBigclass(new BigClass());
goods.getBigclass().setBid(set.getInt("bid"));
goods.getBigclass().setName(set.getString("biname"));
goods.getBigclass().setSid(set.getInt("sid"));
goods.getBigclass().setSname(set.getString("sname"));

//注意，这里的值不可以重复（写错了，把大分类和小分类写在一起了，应该分开）
list.add(goods);

}
return list;

其余都是一样

前台赋值问题

关于前台赋值，如果跨实体的话，先写进的实体，然后写远的，比如，goodslist.brand.name{brand是goods实体类里面的 Brand  品牌 . 品牌实体类的name值}（自己理解）