Add N Times one object

mcorleone · **Joined:** Thu Jul 14, 2005 10:11 am **Posts:** 32

Hello,

I'm having some trouble to add N times one object. Each time i change an attribute (it's a while).

The ID is generated by the database... and i'm calling session.save N times. But i can only insert ONCE.

I'm guessing there is some kind of protection. Can it be overriden ?

Thanks!!!

nathanmoon · **Posted:** Mon Oct 17, 2005 12:22 pm

I'm not sure I understand your post, but if you want to insert N objects, you should construct N objects. You shouldn't re-use the same object and keep passing it to Session.save().

mcorleone · **Joined:** Thu Jul 14, 2005 10:11 am **Posts:** 32

exactly. That's it... i need to insert an object N times. But... each 'time' i change an attribute. It's basically the same object with a property with a different value.

So... i need to instantiate N objects ??... can't i just override that limitation ?

Thank you!!!

nathanmoon · **Posted:** Mon Oct 17, 2005 12:30 pm

You can probably fool Hibernate by setting the id value to null each time, but I'm not sure what other problems that might cause.

mcorleone · **Joined:** Thu Jul 14, 2005 10:11 am **Posts:** 32

thanks Nathan. I'll give it a shot :D

mcorleone · **Joined:** Thu Jul 14, 2005 10:11 am **Posts:** 32

I've just solved it the cool way... no need of creating N objects with different hashcode.

In hibernateUtil class, i just had to add session.clear() to empty the session.

Code:

   public static void add(Object o){      
      HibernateUtil.beginTransaction();
      Session session = HibernateUtil.getSession();      
      session.save(o);session.clear();
   }   

Thanks :D

RobJellinghaus · **Joined:** Thu Jan 08, 2004 6:17 pm **Posts:** 278

You might call this the "cool" way, but it looks kind of weird to me. What kind of id's are being assigned to these objects? Are you nulling out the id of the object when you clear it from the session?

Why *not* just create 10,000 different objects and save them all?

Cheers,
Rob

d · **Joined:** Mon Jul 04, 2005 5:19 pm **Posts:** 720

RobJellinghaus wrote:

Why *not* just create 10,000 different objects and save them all?

the session would cache every one of them

RobJellinghaus · **Joined:** Thu Jan 08, 2004 6:17 pm **Posts:** 278

dennisbyrne wrote:

RobJellinghaus wrote:

Why *not* just create 10,000 different objects and save them all?

the session would cache every one of them

Loading 10,000 objects from the database in a single query is sometimes a problem. But creating and saving them one at a time, perhaps not so much. (If, that is, you can fit them into memory to start with, which you probably can.)

But I understand the issue better now. You might also want to consider using a sequential hi/lo generator (seqhilo) because that might allow Hibernate to batch the inserts more efficiently.

Cheers!
Rob

d · **Joined:** Mon Jul 04, 2005 5:19 pm **Posts:** 720

RobJellinghaus wrote:

... sometimes a problem. But creating and saving them one at a time, perhaps not so much. (If, that is, you can fit them into memory to start with, which you probably can.) ... You might also want to consider using a sequential hi/lo generator (seqhilo) because that might

sometimes ... perhaps ... If ... probably ... might

have you considered a career in politcs ;)

d · **Joined:** Mon Jul 04, 2005 5:19 pm **Posts:** 720

mcorleone - take a look at Session.evict when you get a chance. This way you can remove a single obj instead of all of them.

mcorleone · **Joined:** Thu Jul 14, 2005 10:11 am **Posts:** 32

thanks A LOT for all your replies.

Sorry i'm a day late with the reply.

I dont want to create N objects, because...

i'm writing a system to sell airplane tickets. It's a project for university. Well.. basically, if you've got to register a flight, you need to store N times the entity flight (a flight can be 'done' N times), so you can map the different passengers to different flights.

But... if you've got to create a flight that is done, let's say, every monday, for the next 12 months, and the ONLY difference between them is the date... it doesn't make sense to create 48 objects with a slight difference.

That's why i don't want to create N objects, and instead, change the 'week' in the first object, and add it N times. No need to clone/change attributes. Way more efficient.

Thank you, again :D. Evict is better !