解決hibernate left join fetch 出錯的問題

解決hibernate left  join fetch 出錯的問題

今天寫一個hql,其中用到了 left join fetch ,最後報錯： 

 

//錯誤的寫法：

String hql = "select count(ar) from Article ar left join fetch ar.channel ch where ch.id=?"; 

query specified join fetching, but the owner of the fetched association was not present in the select list [FromElement{explicit,not a collection join,fetch join,fetch non-lazy properties,classAlias=c,role=null,tableName=Student,tableAlias=studentlig1_,origin=classentity classentitylo0_,colums={classentitylo0_.entry_id ,className=com.common.Manger}}]...

查了下資料，發現是我在實體Article中使用了@ManytoOne(fetch=FetchType.EAGER)緣由，在實體中註解指定了fetch後，在hql中就不能再寫fetch了，把fetch去掉，直接能夠成 String hql = "select count(ar) from Article ar left join  ar.channel ch where ch.id=?" 就能夠了。

在Article實體中的配置Channle

@ManyToOne(cascade=CascadeType.REFRESH,fetch=FetchType.EAGER,optional=true)
@JoinColumn(name="cid",nullable=true)
public Channel getChannel() {
return channel;
}

正確的寫法 ： 

String hql = "select count(ar) from Article ar left join  ar.channel ch where ch.id=?"