Eagerly loading multiple collections

tgoorden · **Joined:** Mon Mar 07, 2005 7:25 am **Posts:** 10

Hi, I'm working on a POC for a very large project, but we're having issues with object detachment:

Suppose you have:

Code:

Object A
+collection(B) // lazy loaded
+collection(C) // lazy loaded

basically an object with more than one collection.

Now, using Criteria, try to get a list of A objects that are complete (both collections have been loaded) and detached. For one collection, this is easy to do with setFetchMode("Bs",FetchMode.JOIN). But, there seems to be no way to do this with the collection of Cs as well.

Setting FetchMode.JOIN twice is ignored because of Cartesian product issues. FetchMode.SELECT does a secondary select (to be expected), but this is not done eagerly, so you get a LazyLoadingException anyway.

I've really thouroughly researched this (forum, TFM, Wiki, google and several stabs at the Hibernate source code), but to no avail. Because all the lazy loading is "hidden away" behind the proxying code, it doesn't seem like there's an easy hack anyway.

anthony · **Posted:** Thu Mar 10, 2005 3:57 pm

what about executing 2 queries? one to load b, another for c

hdupre · **Joined:** Thu Jan 20, 2005 3:25 pm **Posts:** 22

tgoorden wrote:

I've really thouroughly researched this (forum, TFM, Wiki, google and several stabs at the Hibernate source code), but to no avail. Because all the lazy loading is "hidden away" behind the proxying code, it doesn't seem like there's an easy hack anyway.

Have you tried the fetch join in HSQL? I think it would do what you want (I'm not sure I understand). If you have an object ob with a collection mycol you can eagerly load it in a HSQL query with "inner join fetch ob.mycol".

Henri.

gavin · **Posted:** Fri Mar 11, 2005 2:16 pm

The correct solution is batch fetching (for now).

HB3 core implements "subselect fetching", but this is not exposed to the user for now.

jrduncans · **Joined:** Tue Mar 01, 2005 10:37 am **Posts:** 17

tgoorden wrote:

Hi, I'm working on a POC for a very large project, but we're having issues with object detachment:

Suppose you have:

Code:

Object A
+collection(B) // lazy loaded
+collection(C) // lazy loaded

basically an object with more than one collection.

Now, using Criteria, try to get a list of A objects that are complete (both collections have been loaded) and detached. For one collection, this is easy to do with setFetchMode("Bs",FetchMode.JOIN). But, there seems to be no way to do this with the collection of Cs as well.

Setting FetchMode.JOIN twice is ignored because of Cartesian product issues. FetchMode.SELECT does a secondary select (to be expected), but this is not done eagerly, so you get a LazyLoadingException anyway.

I've really thouroughly researched this (forum, TFM, Wiki, google and several stabs at the Hibernate source code), but to no avail. Because all the lazy loading is "hidden away" behind the proxying code, it doesn't seem like there's an easy hack anyway.

If you don't care about the second select (you just want to fix the LazyLoadingException), then do this:

Code:

Hibernate.initialize(collection(B));
Hibernate.initialize(collection(C));

swillfah · **Joined:** Wed May 18, 2005 4:50 am **Posts:** 18

Quote:

Setting FetchMode.JOIN twice is ignored because of Cartesian product issues. FetchMode.SELECT does a secondary select (to be expected), but this is not done eagerly, so you get a LazyLoadingException anyway.

In the javadoc (for 3.0.5) it says

Quote:

FetchMode.SELECT - Fetch eagerly, using a separate select. Equivalent to fetch="select".

Is this javadoc wrong? What does "eagerly" mean in this context. Seems to be "lazy" to me ...