I have an object with several collection (defined as set) that are all mapped as lazy=true. In some cases I want to search for objects and get several of its relations (with a criteria query). I can not (do not want to) use every time a FetchMode.Join, because this would explode the resultSet. So, for some collections, I thought of using FetchMode.Select. In the doc I found that this also loads the collection, but with a second query, so perfectly what I wanted. But apparently this does not load the collection.
I know I could do the subqueries myself, but I wanted to use this technic also for deep nested relations and their relations, so that becomes complicated. And the FetchMode.Select seemed perfect for this task.
Is there a workaround? Or do I do something wrong?

My version of Hibernate: 3.2.6
I use the Oracle10gDialect

The relevant part of my mapping:

I tried with fetch="select", fetch="subselect", without fetch, same with lazy: tried with lazy="true", lazy="false", without lazy. This doesn't seem to make any difference.

The relevant part of the code:

Same here: I tried several things: with createAlias, with createCriteria,... but the problem seems really the FetchMode.SELECT, if I change it in FetchMode.JOIN everything works fine, except that it is in this case (of course) all in one query, which I don't want

Hi,
I didn't really understand what you are asking, I'll try to open a discussion:


Are you talking about managed entities?

What do you mean with
?
Do you want the data or not? In some way it most be transported from DB to you entities; if you explaing when and how much (data) we could help to define that.

No, it are just POJO's, but 'deep nested' POJO's: in the example I gave, a user has a Set of Usergroups and Usergroups have themselves Sets of translations and so on (so basically all one-to-many relations). Next to the Set of UserGroups, a User consists also of a Set of UserRoles and a Set of Languages and so on.

So, what I really want to do, is to load one or more users from the database, based on some criteria, with in some cases all the data (the userGroups with translations, the userRoles,...) ideally in one big createCriteria-statement.

I know there are two working options to do so:
1. Define all relations in the mapping as lazy="false". But, I don't want to do that, because I do not always want all related data.
2. create the query and get all related data (for the one-to-many relations) with left join fetch (HQL) or setFechtMode("...", FetchMode.Join) (criteria query). But that doesn't seem as an option to me either, because with too much left joins on one-to-many relations, we would have to deal with the cartesian product problem (see for example http://www.hibernate.org/hib_docs/reference/en/html/queryhql.html). In my example, a fetch join on all relations could still work, but I have other examples where we have objects with a lot more one-to-many relations and several of them again with one-to-many relations. Sot in that case this isn't an option either.

That's why I tried to use the setFetchMode("...", FetchMode.SELECT). In the documentation it is mentioned that this also gets the related data, but in a seperate query and that is exactly what I wanted. But apparently, this doesn't work: the related data is not loaded.
So my question is: how to really load the related data in a seperate query? Do I forget something the way I'm doing it? The relevant piece of code and mapping is in my first post.



So, yes I want the data. And in some cases it is a lot of data with a lot of nested one-to-many relations. I thought of using seperate queries for all one-to-many relations of the first level (so for example the userGroups of the user) and a left join fetch on the relations of the second level (so for example the translations of the userGroups).

Well most hibernate applications are like this, the whole problem you are explaining is the reason for hibernate's existence ;-)

Managed entities are POJO's, only Hibernate is automagically adding the data to them when you need it, you just need to use it the correct way so that a connection to the DB stays open until you're finished with the current transaction.

Is this your first hibernate application?

No, this is not my first Hibernate application, but I have to admit, it is the first one that is so complex and big. But, yes, I have some Hibernate experience.



I know that and I know that when the connection is still open, I can just let Hibernate get the data, for example when I call (in my example) user.getUserGroups() or with Hibernate.initialize. That is a sollution, but in my opinion asking a subselect directly in the base query would be nicer like in my code-example above. In the sollution of getting the data after the query (with getters of with Hibernate.initialize), when I have several users as result, I have to loop through the users and do for each one a getUserGroups(). And so on for relations on this relations. Ok, I can do that, but it seemed a lot nicer to me to use the fetchMode.SELECT. So, my only question was: why does the fetchMode.SELECT doesn't load me the data (see first post for explanation and code)?
The only thing I want to do, is to have a method in my dao that gives me all users corresponding to some criteria with the wanted relations (given as a parameter in the method). And I thought (reading the doc) that this would be possible with a fetchMode.SELECT (why I don't want to use fetchMode.JOIN on all relations, I explained clearly in my posts above).

I also know that (in HQL) I can add the userGroups in my select, so that I get users and userGroups, but that way I would have to loop through the results and see what objects it are, when I want to construct my users as objects with userGroups. OK, that also is a possibility, but that's not my question. I'm just wondering why this doesn't work in one statement, without loops, not using left join fetch on all relations.
I can do it, that's not the point, but I wanted to do it nicely and I don't see why this doesn't work with the fetchMode.SELECT.

I use annotation configuration. You need use subselect fetch.

Example configuration:
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "message_tag", joinColumns = {@JoinColumn(name = "message_id")},
inverseJoinColumns = {@JoinColumn(name = "tag_id")})
@Fetch(value = FetchMode.SUBSELECT)
public Set<Tag> getTags() {
return tags;
}


After this you must access collection before session closed or use not lazy fetch.
http://www.hibernate.org/hib_docs/v3/re ... erformance
19.1
Subselect fetching - a second SELECT is used to retrieve the associated collections for all entities retrieved in a previous query or fetch. Unless you explicitly disable lazy fetching by specifying lazy="false", this second select will only be executed when you actually access the association.