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Posted to ojb-user@db.apache.org by Robert J Celestino <Ro...@sas.com> on 2003/10/31 03:14:16 UTC
o/r mapping question
Hello all,
I am stumped by what is posibly a very simple mapping problem.
Consider something like this
Person is stored in the person table
Person has-a AddressGroup. AddressGroup is not stored in the DB
AddressGroup has a list of Addresses
Address is stored in the address table. Has a column
called PersonId that indicates the person it belongs to
This is a little contrived but bear with me.
Clearly Person could have a list of addresses, but for various reasons it has the intermediate class AddressGroup instead.
I know how to solve this if AddressGroup was stored in the DB, but it is not. It is purely a domain class.
How can I get ojb to create and write this class without actually writing it to the db?
Thanks very much
Bob c
----------------------------------------------------------------
Bob Celestino
SAS Research and Development
919 - 531 - 9425
robertj.celestino@sas.com
SAS - The Power to Know
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Re: o/r mapping question
Posted by Brian McCallister <mc...@forthillcompany.com>.
Solution 1:
Implement AddressGroup as a custom collection (implementing Manageable
Collection) used to hold the address instances. This muddies the domain
model a bit as AddressGroup then needs to know about
ManageableCollection.
Solution 2:
Map two classes to the same table (I used an existing application hence
the names of tables):
kim=# \d users
\d Table "public.users"
Column | Type | Modifiers
------------+------------------------+-----------
id | integer | not null
handle | character varying(32) |
password | character varying(255) |
first_name | character varying(255) |
last_name | character varying(255) |
aim_name | character varying(255) |
email | character varying(255) |
Indexes: users_pkey primary key btree (id)
kim=# \d gifts
Table "public.gifts"
Column | Type | Modifiers
-----------------+-------------------------+-----------
id | integer | not null
name | character varying(255) |
description | character varying(2000) |
level_of_desire | integer | default 0
where_to_buy | character varying(2000) |
cost | character varying(255) |
for_user_id | integer | not null
from_user_id | integer |
suggest_user_id | integer |
Indexes: gifts_pkey primary key btree (id)
Foreign Key constraints: gifts_fk_1 FOREIGN KEY (suggest_user_id)
REFERENCES users(id) ON UPDATE NO ACTION ON DELETE NO ACTION,
gifts_fk_2 FOREIGN KEY (for_user_id)
REFERENCES users(id) ON UPDATE NO ACTION ON DELETE NO ACTION,
gifts_fk_3 FOREIGN KEY (from_user_id)
REFERENCES users(id) ON UPDATE NO ACTION ON DELETE NO ACTION
kim=#
<class-descriptor class="org.skife.kim.model.Foo" table="USERS">
<field-descriptor name="id" column="ID" jdbc-type="INTEGER"
primarykey="true" autoincrement="true"/>
<reference-descriptor name="bar"
class-ref="org.skife.kim.model.Bar">
<foreignkey field-ref="id"/>
</reference-descriptor>
</class-descriptor>
<class-descriptor class="org.skife.kim.model.Bar" table="USERS">
<field-descriptor name="id" column="ID" jdbc-type="INTEGER"
primarykey="true" autoincrement="true"/>
<collection-descriptor name="gifts"
element-class-ref="org.skife.kim.model.Gift"
collection-
class="org.apache.ojb.broker.util.collections.ManageableHashSet">
<inverse-foreignkey field-ref="for_user_id"/>
</collection-descriptor>
</class-descriptor>
<class-descriptor class="org.skife.kim.model.Bang" table="GIFTS">
<field-descriptor name="id" column="ID" jdbc-type="INTEGER"
primarykey="true" autoincrement="true"/>
<field-descriptor name="for_user_id" column="FOR_USER_ID"
jdbc-type="INTEGER" access="anonymous"/>
<reference-descriptor name="bar"
class-ref="org.skife.kim.model.User">
<foreignkey field-ref="for_user_id"/>
</reference-descriptor>
</class-descriptor>
public class Foo
{
public Integer id;
public Bar bar;
}
public class Bar
{
public Integer id;
public Set gifts;
}
public class Bang
{
public Integer id;
public Bar bar;
}
public void testFooBar() throws Exception
{
foo = new Foo();
bar = new Bar();
bang = new Bang();
PersistenceBroker broker =
PersistenceBrokerFactory.defaultPersistenceBroker();
foo.bar = bar;
bar.gifts = new HashSet();
bar.gifts.add(bang);
bang.bar = bar;
broker.store(foo);
broker.store(bar);
broker.store(bang);
broker.clearCache();
Criteria crit = new Criteria();
crit.addEqualTo("id", this.foo.id);
Query query = new QueryByCriteria(Foo.class, crit);
Foo thing = (Foo) broker.getObjectByQuery(query);
Assert.assertEquals(thing.id, foo.id);
Assert.assertEquals(1, foo.bar.gifts.size());
}
.
Time: 2.108
OK (1 test)
Neither one is ideal, but the ideal is having the data model and object
model match up perfectly. The second leaves your object model
independent of your persistence mechanism at least but sort of feels
dirty to me.
-Brian
On Thursday, October 30, 2003, at 09:14 PM, Robert J Celestino wrote:
> Hello all,
>
> I am stumped by what is posibly a very simple mapping problem.
>
> Consider something like this
> Person is stored in the person table
> Person has-a AddressGroup. AddressGroup is not stored in the DB
> AddressGroup has a list of Addresses
> Address is stored in the address table. Has a column
> called PersonId that indicates the person it belongs to
>
> This is a little contrived but bear with me.
>
> Clearly Person could have a list of addresses, but for various reasons
> it has the intermediate class AddressGroup instead.
>
> I know how to solve this if AddressGroup was stored in the DB, but it
> is not. It is purely a domain class.
>
> How can I get ojb to create and write this class without actually
> writing it to the db?
>
> Thanks very much
> Bob c
>
> ----------------------------------------------------------------
> Bob Celestino
> SAS Research and Development
> 919 - 531 - 9425
> robertj.celestino@sas.com
>
> SAS - The Power to Know
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
> For additional commands, e-mail: ojb-user-help@db.apache.org
>
>