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mapping two key columns for a set

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intbos-tech

Post subject: mapping two key columns for a set

Posted: Sun Aug 05, 2007 6:19 pm

Newbie

Joined: Sun Jul 29, 2007 3:34 pm
Posts: 3

Hi,

Can I map two foreign key constraints to one collection? I have a user class which has a set of friendship objects. Friendship objects have two users. I can't see this kind of example anywhere. When I try the following code, it doesn't work. Can anybody tell me the correct way of doing this?

Thank you so much for your help!!!!

Code:

    DbUser.hbm.xml
    <set name ="Friendships" table="Friendships" cascade="none">
        <key column="A" />
        <key column="B" />
        <one-to-many class="sn.Friendship,sn">
    </set>

   Friendship.cs
    public class Friendship : BaseNHibernateClass<Friendship, int>
    {
        private int _id;
        private DbUser _a;
        private DbUser _b;
        .............

    DbUser.cs
    public class DbUser : BaseNHibernateClass<DbUser, Guid>
    {
        private Guid _id;
        private string _name;
        private ISet<Friendship> _friendships;
        .............

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pelton

Post subject:

Posted: Mon Aug 06, 2007 6:55 pm

Regular

Joined: Fri Jan 27, 2006 2:32 pm
Posts: 102
Location: California, USA

Two comments:

First, if there is a relationship between DBUser and Friendship, then map that relationship. Use the ID of the Friendship to make the join. I think the properties of Friendship are irrelvant (so far as the collection mapping is concerned).

Code:

<set name="Friendships" ...>
  <key column="FriendshipID">
</set>

But, this data model makes my head hurt. A User has several friendships, of which is made up of two other users??

So, John has a friendship with (Sally / Jane) and (John / Tim)??

Or, is it more like John has friendships with Sally, Jane, John and Tim??

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intbos-tech

Post subject:

Posted: Mon Aug 06, 2007 7:28 pm

Newbie

Joined: Sun Jul 29, 2007 3:34 pm
Posts: 3

Hi, thank you for your time.

DBUser John has a friendship which contains two users. Himself and a friend.

If a Friendship object has A=John and B=Jane, then I want this friendship to be in both John's collection and B's collection. So when I go John.Friendships, it should contain this friendship object. And when I go Jane.Friendship, it should also contain the same friendship object.

Is there a good way to map this?

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jchapman

Post subject:

Posted: Tue Aug 07, 2007 7:51 am

Senior

Joined: Thu Feb 09, 2006 1:30 pm
Posts: 172

intbos-tech wrote:

Is there a good way to map this?

On user look at a many-to-many set. Look at the docks for the many-to-many section. Your table design is already set up for it. This will remove the intermediate object and instead give you a list of all friends for John instead of having to look through "friendships".

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