用Hibernate防止无限循环数据检索 [英] Preventing infinite loop data retrieval with Hibernate

问题描述

我想知道：假设一个场景，例如

// POJO

  public class User {
 
 private String userName; 
私人字符串名称; 
私人字符串姓氏; 
私人列表< Blog> blogList; 
 
 //在这里找到所有获得者和设置者，并假设他们已经生成。 
} 
 
 public class Blog {
 private String title; 
私人字符串内容; 
私人用户作者; 
私人日期datePublished; 
私人日期dateLastModified; 
 
 //所有getter和setter都已经生成（通过Eclipse或NetBeans）
} 
  

想象一下，这些对象已被正确映射到它们各自的Hibernate配置文件中。

我的问题：

我如何检索我的用户，并在代码级别列出所有用户博客？ （即，不允许hibernate自动为我填充 blogList 。
我想添加分页（即从列表5中检索20列表），并且如果您仔细想想，这可能是一个无限循环，因为Blog有一个用户实体，它有一个 List< Blog> 实体。

如何防止这种情况发生？

PS只是出于好奇，我如何让Hibernate在配置端填充我的 blogList ？

预先感谢。

解决方案

• Hibernate检测到这样的循环并且不让它们发生。可以使用fetch type = lazy（ fetchType = FetchType.LAZY ）标记您的集合，以便在拥有对象

时不会获取集合元素
• 可以通过 setFirstResult（..）和 setMaxResults（）来使用 Query 。 。）为了实现分页。（并且摆脱co然后选择）

I was wondering: Imagine a scenario where e.g.

//POJO

public class User {

   private String userName;
   private String name;
   private String surname;
   private List<Blog> blogList;

   //All getters and setters are found here and assume they're generated.
}

public class Blog {
    private String title;
    private String content;
    private User author;
    private Date datePublished;
    private Date dateLastModified;

    //All getters and setters have been generated (by Eclipse or NetBeans)
}

Imagine that these objects have been correctly mapped into their respective Hibernate configuration files.

My question:

How would I retrieve my user with the list of all the user blogs on code level? (i.e., not allow hibernate to populate blogList automatically for me. I want to add paging (i.e. from list 5, retrieve 20 list) and also, if you think carefully, this might be an infinite loop as a Blog has a User entity which has a List<Blog> entity.

How do I prevent this?

PS Just out of curiousity, how would I let Hibernate populate my blogList on the configuration side?

Thanks in advance.

解决方案

• Hibernate detects such loops and doesn't let them happen
• You can mark your collection with fetch type=lazy (fetchType=FetchType.LAZY) so that the collection elements are not fetched when the owning object is
• you can used a Query with setFirstResult(..) and setMaxResults(..) in order to achieve paging. (and get rid of the collection then)

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