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bidirectional one-to-many mappingwith interface involved

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danz8086

Post subject: bidirectional one-to-many mappingwith interface involved

Posted: Tue Mar 16, 2004 12:07 pm

Beginner

Joined: Tue Mar 02, 2004 6:17 pm
Posts: 20

Hi,

I'm wondering how to map the class hierarchy below, given the condition that classes A1 and A2 need to have independant Id colums (table-per-concret class as I understood).

Code:

interface A {}

class A1 implements A{
  private Map collectionC;
}

class A2 implements A{
  private Map collectionC;
}

class C {
  private A parent;
}

I tried this mapping, but it requires a mapping exists for interface A - this (as my understanding) will force me into the table-per-subclass scenario.

Could anyone advise on how can I map the relationship with table-per-concret class method?

Code:

<class name="A1">
  ...
  <map name="collectionC" inverse="true">
    <key column="parentId"/>
    <index column="keyC">
    <one-to-many class="C">
  </map>
</class>

<class name="A2">
  ...
  <map name="collectionC" inverse="true">
    <key column="parentId"/>
    <index column="keyC">
    <one-to-many class="C">
  </map>
</class>

<class name="C">
  ...
  <many-to-one class="A" column="parentId">
</class>

regards,
Dan

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danz8086

Post subject: one-to-many collection: java.util.Map and <any>

Posted: Tue Mar 16, 2004 4:24 pm

Beginner

Joined: Tue Mar 02, 2004 6:17 pm
Posts: 20

I also tried this:

Code:

<any name="parent" meta-type="class" id-type="long">
  <column name="PARENT_CLASS" />
  <column name="PARENT_ID" />
</any>

But this seems not working with the <map> collection of class A1 and A2. Basically, the mapping will generate a table for class C like this:

<column unid>
<column parent_class>
<column parent_id>
<column parentid>

The last column is created because there is a <key column="parentId"> line in the <map> statements for classes A1 and A2.

When I call C.setParent(A1) and persist the objects, the "parentId" column is empty because it is not in the "many-to-any" mapping.

If I change the key to <key column="parent_Id"/> (which is same as the "any" declaration), I will get "duplicate column name" error.

So, can I use java.util.Map for one-to-many collections after all if there is an "any" on the "many" end?

Dan

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danz8086

Post subject:

Posted: Thu Mar 18, 2004 12:35 pm

Beginner

Joined: Tue Mar 02, 2004 6:17 pm
Posts: 20

Well, it turned out to be a problem to cases: if I change the collection mapping's key column (parent_id) to exactly the same (PARENT_ID) as in the <any> mapping, everything works fine now.
Just curious about one thing:
<any> doesn't currently support "lazy" attribute. Is it possible to add this support after all? Or is there a way around?

It would be more efficient in the following scenario:

Code:

class A1 implements A{
  private Collection collectionOfB;
}
Class A2 implements A{
  private Collection collectionOfB;
}
class B {
  private A parent;
}

I use a one-to-many for A1 and A2 to associate B collection. And use "any" to map the many-to-one from B to A1 or A2 (which is the simplest way came out of my mind).

When I load B using a query like "from B where B.timeStamp>:today", I don't necessarily always want to load A, or call B.getParent(). 

Regards,
Dan

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