My problem is:
1. The top-level class A holds an array of N (hundreds) second-level classes B. I would like to have each class B in this array as a COLUMN in the table, which represents A. However, standard Hibernate options map array elements to ROWS.

2. Each class B in the above-mentioned array, in turn, holds a sub-array of M (again, hundreds) items - now, simple numbers, rather than entities. I would like to have this array, again, map to COLUMNS in a table, which represents B.

The endpoint I would like to have in the database is: when a top-level item A is added to the database, the following events take place:
- a new row in the 2-column or 3-column A-table is added;
- a new row in the N-column B-table is added;
- N new rows in the M-column C-table are added.

Tried to implement this using explicit declaration of N B-components in class A and M C-components in class B, but to no avail. I don't post the mappings because there are too many versions: with one-to-many, with composite-element, etc. If somebody cares to give me a hint, I would at least know what direction to pursue.
Thanks for any help.

What you actually want can be done using 100 many-to-one in A, but it sucks a lot.
Why don't you adopt the traditional relational db usage (FK to a in B table)? And thus the hibernate way of one-to-many.

Thank you, I have, finally, implemented it in more or less the way you've described:

Class A contains an array of classes B mapped as one-to-many
<array name="Bs" inverse="false" cascade="all">
<key column="A_ID"/>
<index column="B_NUM"/>
<one-to-many class="all.B"/>
</array>

Class B contains 128 instances of class C mapped as:

<class name="all.B" table="B" dynamic-update="false" dynamic-insert="false">
<id name="id" column="B_ID" type="int" unsaved-value="0">
<generator class="native"> </generator> </id>
<many-to-one
name="C1" <!-- And so on to C128 -->
class="all.C"
cascade="all"
outer-join="auto"
update="true"
insert="true"
column="S1" <!-- And so on to S128 -->
not-null="false"
unique="false" />
</class>

Class C contains 400 integer properties:
<class name="all.C" table="C" dynamic-update="false" dynamic-insert="false">
<id name="id" column="C_ID" type="int" unsaved-value="0" >
<generator class="native"> </generator> </id>
<property
name="s1" <!-- And so on to s400 -->
type="integer"
update="true"
insert="true"
column="S1" <!-- And so on to S400 -->
not-null="true"
/>
</class>


Presently, it works, but on
session.save(a);
I get an Out of memory exception. It does not appear if there are less B's in A (20 or so). There is a lot of available memory, though. We work with Postgres 7.4 Seems something should be done to cache settings - can't you tell what?

As you've mentioned, the whole idea seems to suck quite a bit, especially because most of time I don't need to load or save the whole of A, only several B's. CAN YOU SUGGEST A BETTER WAY?

Generally, the problem is common: mapping a multidimensional OLAP cube to relational structure. Maybe, there is some standard way to do this in Hibernate? Because this problem is quite general, I have posted it also to Application Architecture section.
Thanks.

Granted that I know zippo about what an OLAP cube is...

You have 128 many-to-one relationships. How about using many-to-many and programmatically restricting the number?

Or how about something like the ternary associations example from the manual (section6.10)



http://www.hibernate.org/hib_docs/reference/html/collections.html#collections-s1-11a