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Hibernate version: 2.1.8

Name and version of the database you are using:Oracle 9i

I have the same situtation that was asked in this forum thread: http://forum.hibernate.org/viewtopic.php?t=929721&highlight=one+collection+role+may+fetched+query



However the thread appears to end before the question was answered.



And I know about

From other threads it appears that maybe I can achieve this doing 2 queries as opposed to n+1, but I'm not sure how to exaclty this should work. Is there a sample somewhere? Would I execute find twice within the same session, with the two queries? Am I barking up the wrong tree with the two queries, is there another way to avoid the n+1?

Thanks.

If you have a <many-to-one> reference from B to C, and a <many-to-one> reference from B to A, with outer-join="true", then you could perform a query on C.class to return a list of all C associated with A. That would not initialize A's collection of Bs or B's collection of Cs, but it would give you all of the Cs your are interested in (with references back to B and ultimately A). Depending on how you are using the objects, that may be a quick-and-dirty workaround for the 1+m*n selects problem you are having, but it does have some interesting implications if you are trying to add or remove Bs from A or Cs from B.

You could set outer-join="true" on the <set> of Bs in A or the <set> of Cs in B to change 1+m*n selects to just 1+n or 1+m selects. Which one is up to you, but it would make sense to choose the one that is potentially larger. For example, if the average number of Bs in any given A exceeds the average number of Cs in any given B, then put the outer-join="true" on the <set> of Bs in A. I don't know the particulars, but setting a batch-size on the <class> may also improve performance.

Other than that, I don't know. Depending on your caching strategy you can minimize the number of times that you have to take the 1+m*n hit...if you load up the collections and put them in your user session as detached objects, for example, then you control when they are loaded/refreshed. For example, I have a similar heirarchy with user-role-permission that I load once per user session and keep independent of the Hibernate session or application transactions. It's a significant hit during the log-in process, but that's the only time it hurts.

- Jesse

Another (much better) approach is to use HB3 subselect fetching.

Before I make a jump to ver 3, I'd like to take a look at this. Is there any documentation for this? The doc currently says: TODO

Thanks.

I follow davout asking for a documentation. The feature is exactly that what I wanted, but it would be interesting to know "how".

Taking a look into the DTD of hibernate3 offers that the fetch attribute of set, bag etc. can take the argument "subselect".

I assume it could be done this way:

[code]
<class name="sample.Entity" table="ENTITY">

<id name="id" type="long">
<column name="ENTITY_ID" not-null="true" />
<generator class="native" />
</id>

<set name="properties" table="ENTITY_PROPERTY" lazy="false" cascade="all-delete-orphan" fetch="subselect">
<key column="ENTITY_ID" />
<many-to-many class="sample.Property" column="PROPERTY_ID" />
</set>
[code]

Am I right?[/b][/code]