这些是类Country
和State
:
国家:
@Entity
@Table(name="Country")
public class Country{
@Id
private String countryName;
private String currency;
private String capital;
@OneToMany(mappedBy="country", cascade=CascadeType.ALL, fetch = FetchType.LAZY)
private List<State> statelist = new ArrayList<State>();
州:
@Entity
@Table(name="State")
public class State{
@Id
private String stateName;
private String language;
private long population;
@ManyToOne
@JoinColumn(name="countryName")
private Country country;
HQL 查询应该是什么来检索特定国家/地区人口最多的州(也许在列表中(?
这是我编写的代码,其中,我尝试首先检索最大人口值,然后运行该国家/地区的所有州,以匹配每个人口值,并将州添加到列表中。但是,在这样做时,我收到错误,即查询中定义的列不明确。
public List<State> stateWithMaxPopulation(String countryName){
List<State> l = new ArrayList<State>();
Country ctr = (Country)session.get(Country.class,countryName);
String hql = "select max(stlst.population) from Country cntry "
+" join cntry.statelist stlst where countryName=:cNm";
Query query = session.createQuery(hql);
query.setParameter("cNm", countryName);
Long maxPop = (Long)query.uniqueResult();
for(State st : ctr.getStatelist()){
if(st.getPopulation() == maxPop)
l.add(st);
}
return l;
}
正确的方法应该是什么?
您缺少实体的别名
select max(stlst.population) from Country cntry " +" join cntry.statelist stlst where cntry.countryName=:cNm1