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Hibernate M:M mapping plu

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  Hibernate M:M mapping plu "Spendius" <spendius@THRWHITE.remove-dii-this> - 2011-04-27 15:21 +0000
    Re: Hibernate M:M mapping "Axel Hallez" <axel.hallez@THRWHITE.remove-dii-this> - 2011-04-27 15:21 +0000

#24 — Hibernate M:M mapping plu

  To: comp.lang.java.databases
Hello,

I'm asking a question already asked a few years ago:
http://groups.google.be/group/comp.lang.java.databases/browse_frm/thread/c3a1045674b6b65f/c3aa99a30b22c8e6?hl=nl&lnk=gst&q=%22many-to-many%22&utoken=DT02DTsAAAAYHYTsDrEdq7-NnfRgl-Nk4GfRPBFGhDGPHFrvVDkRvgz1eTbjLK36WL5svdAfvL03TRB4SbQHh5KfXKICx3ka

When your middle table (that which relates your 2 tables
through a many-to-many relationship) contains more than
the A_ID and B_ID columns but also -for ex.- DATE columns
etc.- is there a way to deal with this extra info with some
more config in your .hbm.xml files or do you really need a
supplementary class to handle this data ?

When you have no more than the 2 ID columns to deal with,
the following mappings are enough:
<set name="events" table="PERSON_EVENT">
<key column="PERSON_ID"/>
<many-to-many column="EVENT_ID" class="Event"/>
</set>
in a file and
<set name="participants" table="PERSON_EVENT" inverse="true">
<key column="EVENT_ID"/>
<many-to-many column="PERSON_ID" class="Person"/>
</set>
in the other .hbm.xml file... And no specific class for the
PERSON_EVENT database table is required - but when this
table contains other columns, is there no way but to create
another class to play with this extra columns ?

In advance, thanks.
Regards,
Spendius

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#34 — Re: Hibernate M:M mapping

  To: comp.lang.java.databases
Spendius wrote:
> When your middle table (that which relates your 2 tables
> through a many-to-many relationship) contains more than
> the A_ID and B_ID columns but also -for ex.- DATE columns
> etc.- is there a way to deal with this extra info with some
> more config in your .hbm.xml files or do you really need a
> supplementary class to handle this data ?
> 
> When you have no more than the 2 ID columns to deal with,
> the following mappings are enough:
> <set name="events" table="PERSON_EVENT">
> <key column="PERSON_ID"/>
> <many-to-many column="EVENT_ID" class="Event"/>
> </set>
> in a file and
> <set name="participants" table="PERSON_EVENT" inverse="true">
> <key column="EVENT_ID"/>
> <many-to-many column="PERSON_ID" class="Person"/>
> </set>
> in the other .hbm.xml file... And no specific class for the
> PERSON_EVENT database table is required - but when this
> table contains other columns, is there no way but to create
> another class to play with this extra columns ?

If you don't wrap the extra attributes in a class, how would you be able 
to manage them?
If a many-to-many relationship has extra attributes, this generally 
means that the relationship entries are entities in their own right.

Now I guess that one could come up with some schema to avoid the 
definition of an extra class, but I can't imagine that this would be 
easier to deal with.

Kind regards,
Axel Hallez

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