aspose file tools*
The moose likes Object Relational Mapping and the fly likes Collection Mapping Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Databases » Object Relational Mapping
Bookmark "Collection Mapping" Watch "Collection Mapping" New topic
Author

Collection Mapping

subhashchandra medhiassam
Ranch Hand

Joined: Sep 10, 2008
Posts: 72
Hi all,
I am new to Hibernate. I am entangled with Collection-Mappping.I need some good tutorial having complete example program on Collection Mapping.

Also, i tried the following to test Collection mapping.

I wrote the following POJO class:


I wrote the following class to persist an object of type Book into the MYSQL database running on local host:




The following is the content of my mapping file:



When run the second program, i am getting the following output:
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
null
Exception in thread "main" java.lang.NullPointerException
at roseindia.tutorial.hibernatecollection.BookInsert.main(BookInsert.java:52)

The line where the NullPointerException took place corresponds to:

session.flush();

Kindly let me know where i could have gone wrong.
Paul Sturrock
Bartender

Joined: Apr 14, 2004
Posts: 10336

So you are trying to flush a session that is null. So I would assume that something has gone wrong in these two lines:

What other exception messages do you have in your log? Has the SessionFactory been properly configured? Is the DataSource valid and can you connect to the database.
[ September 11, 2008: Message edited by: Paul Sturrock ]

JavaRanch FAQ HowToAskQuestionsOnJavaRanch
Cameron Wallace McKenzie
author and cow tipper
Saloon Keeper

Joined: Aug 26, 2006
Posts: 4968
    
    1

As far as finding tutorials on collection mapping, might I suggest my own?

I've got some very simple and straight forward examples on how to map one to one, one-to-many and many-to-many associations. Many people have found these tutorials very helpful.

Mapping Collections with Hibernate

-Cameron McKenzie
 
wood burning stoves
 
subject: Collection Mapping