Hibernate继承，Collections和@OrderedBy超类属性生成MySQL语法错误 [英] Hibernate inheritance, Collections and @OrderedBy superclass attribute generates MySQL syntax Error

问题描述

我使用Hibernate 3.6.1来映射三个实体

$ pre $ @ $ e
@Inheritance（strategy = InheritanceType .JOINED）
公共类条目{
私有长ID;
私人日期publishedAt;

@Id
public getId（）{...}

...
}

@Entity
public class Category {
private Long id;

列表< Podcast>播客;

@Id
public getId（）{...}

@OneToMany（mappedBy =category，cascade = {CascadeType.ALL}，fetch = FetchType.EAGER）
@OrderBy（publishedAt）
public List< Podcast> getPodcasts（）{
返回播客;


code

  @Entity 
 public class Podcast extends Entry {
 
 private Category category; 
 
 @ManyToOne（fetch = FetchType.EAGER）
 public PodcastsCategory getCategory（）{
 return category; 
 
 
 
 
 $ b如果我试图获取一个类别实例，我得到一个异常
  com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException ：'订单子句'中的未知列'podcasts0_.Entry.publishedAt'
  
什么导致此异常？这个映射有什么问题？ 
解决方案
这是由以下错误导致的： HHH-3577使用连接的子类时，按顺序错误地使用了SQL。
 
 
 
可以在 podcasts上删除 @OrderBy 和 fetch = FetchType.EAGER  和使用下面的查询加载类别，而不是 get（）： 
 
 
  SELECT DISTINCT c 
 FROM Category c LEFT JOIN FETCH c.podcasts p 
 WHERE c.id =？ 
 ORDER BY p.publishedAt 
  
 
I' using Hibernate 3.6.1 to map three entities 
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Entry {
   private Long id; 
   private Date publishedAt; 

   @Id
   public getId() {...}

   ...
}

@Entity
public class Category {
   private Long id; 

   List<Podcast> podcasts;

   @Id
   public getId() {...}

   @OneToMany(mappedBy = "category", cascade = {CascadeType.ALL}, fetch = FetchType.EAGER)
   @OrderBy("publishedAt")
   public List<Podcast> getPodcasts() {
      return podcasts;
   }
}
and
@Entity
public class Podcast extends Entry {

   private Category category; 

   @ManyToOne(fetch = FetchType.EAGER)
   public PodcastsCategory getCategory() {
      return category;
   }
}
If i try to fetch a Category instance, i get an Exception 
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'podcasts0_.Entry.publishedAt' in 'order clause'
What causes this exception? Whats wrong with this mapping? 
解决方案
It's caused by the following bug: HHH-3577 Wrong SQL in order by clause when using joined subclasses.


As a workaround you can remove @OrderBy and fetch = FetchType.EAGER on podcasts and load category using the following query instead of get():
SELECT DISTINCT c 
FROM Category c LEFT JOIN FETCH c.podcasts p
WHERE c.id = ?
ORDER BY p.publishedAt


                        
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