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为什么在hibernate中用list影射one-to-many时，在查询数据时，经常有null值

 Learned a little this weekend - Bag vs List in Hibernate.  I was troubled since i really wanted to have a Java ArrayList in my object so i could index in my jsp and iterate over the list in an update form.  Using a Hibernate Set left me unable to index.  A Hibernate List left the Java ArrayList populated using the primary key - if the keys were 0,1,2,... that would have been ok.  But i only needed a few items from the database in my ArrayList and since the Hibernate List maintains the position of the object in the ArrayList equal to the position in the database the technique was leaving holes in my ArrayList of nulls.  Of course this was not what i wanted.  Now this may be explained in the documentation but after reading it twice i did not fully understand the Hibernate List.  Over the weekend i read the book Hibernate in Action and discovered the Hibernate Bag and it solved my problem.  I can use a Java ArrayList that is loaded simply by adding new objects to the beginning of the ArrayList.

posted on 2007-04-05 16:50 lqx 阅读(989) 评论(0)  编辑  收藏




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