Hi,
Schmidt wrote:
Hi Armin,
Thank you for the answer.
I'm using the 1.0.4 version. And the same problem happens with 1:n
associations as well.
If you use lazy loading with 1:n or m:n relation OJB always create a
collection proxy object (this helps to avoid a DB query on object
materialization). Recommended way to check n-side existence is to use
Collection.size() method. In this case OJB performs a count-query to
verify the number of the n-side objects.
In the 1:n associations I set auto-retrieve="false"
and proxy="dynamic". As my classes do not implement interfaces, I'm using
CGLib as ProxyFactoryClass.
The setting proxy="dynamic" is an illegal attribute value for reference-
and collection-descriptors (only true/false is valid). It doesn't make
sense (please correct me if am wrong) to use auto-retrieve="false"
(prevent materialization of the 1:n or m:n relation)
http://db.apache.org/ojb/docu/guides/basic-technique.html#Setting+Load%2C+Update%2C+and+Delete+Cascading
in combination with proxy="true" (lazy-loading).
I debugged the source code and verified that the collection representing the
n side of the 1:n association is filled with proxy references. That's good
because the real object are not materialized, but when I check for nullity,
the result is false due to proxy references. The solution (ugly) to bypass
this problem is in the ProxyHelper.getRealObject method. But this solution
is invasive, proxies should be transparent.
Please use Collection.size()
Another problem that came up after I started using proxies is in the
hierarchy mapping. I'm using just one table to map my class hierarchy. So,
this table has a CLASSNAME field to identify which class to load. In the
constructor of my base class I have a
setOjbConcreteClass(this.getClass().getName()) call. Before using proxies,
the class name was configured correctly. But after, instead of having the
real object class name, the application configures the classname field using
the proxy class name.
I assume there should be something wrong with my mapping files or some other
point in my application. As said earlier, I believe proxies should be
transparent. Did someone here experience the same problems?
Hm, I will have a look at this tomorrow (will try to reproduce your issue).
regards,
Armin
Thank you again!
Armin Waibel wrote:
Hi,
Schmidt wrote:
Hi,
Consider that an object A has an association with an object B. Also that
dynamic proxies are in use so that when object A is loaded, a proxy to B
is
created and the object B itself is not materialized. Sometimes, before
taking an action, I need to verify if there is a B object associated to
A.
This check is done as follows:
if (a.getB() == null) {...}
The problem is that even if there isn't a B associated with A, OJB
returns
false because there is always a proxy between A and B. The check is
actually
done using the proxy reference which is always present.
How can we handle that?
Which version of OJB do you use? I try to reproduce this with the
current source (OJB_1_0_RELEASE branch) without success. If class
Article has a 1:1 relation to ProductGroup and I search for an Article
without a ProductGroup I get:
Criteria c = new Criteria().addEqualTo("articleName", name + "without
PG");
q = QueryFactory.newQuery(ArticleWithReferenceProxy.class, c);
Article br = (ArticleWithReferenceProxy) broker.getObjectByQuery(q);
assertNotNull(br);
assertNull(br.getProductGroup());
Could it be that the association between A and B is a 1:n relation?
regards,
Armin
Thank in advance!
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