update join table

MichaelNorman · **Joined:** Thu Aug 17, 2006 5:43 pm **Posts:** 2

Dear all.

I am quite a hibernate beginner, so please excuse if my question seems simple.
I have the following mapping:

Code:

<class name="User" table="users">
   <id name="uid" column="uid">
      <generator class="native" />
   </id>
   <join table="server">
      <key column="uid" unique="true" />
      <many-to-one name="server"
         class="ServerName" column="serverId" not-null="true" />
   </join>
</class>
<class name="ServerName" table="serverNames">
   <id name="serverId" column="serverId">
      <generator class="native" />
   </id>
</class>

So I have three tables:

Code:

table users ( uid bigint not null primary key )
table server ( uid bigint not null primary key, serverId bigint not null )
table serverNames ( serverId bigint not null primary key )

All works fine, I can instantiate the appropriate classes, no problems so far. But now I have some understanding problem. How can I update the table "server", i.e. I want to asign another serverId to a given uid, i.e. I want to update the join table... how can I access the join table and update it via hibernate?

How you can help me, thanks in advanced,

greetings,

Norman[/code]

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

With the mapping you have, you'd use user.setServer(server). However, I think it unlikely that your mapping is correct. You've said that a User is made up of data from two tables, users and server. I think it's more likely that User is made up of data only from the users table, and a User has an associated server. It's possible that a server is made up of data from two tables, server and serverNames. Though if a server can have more than one name, then it would be more correct to map this as a server containing a collection of names. Finally, guessing from the shape of the tables, and the fact that you've called server a join table, I'm going to say that you actually want a many-to-many mapping between users and serverNames.

This is probably the mapping that you're looking for:

Code:

<class name="User" table="users">
   <id name="uid" column="uid">
      <generator class="native" />
   </id>
   <set name="servers" table="server">
     <key column="uid" not-null="true">
     <many-to-many class="ServerName" column="serverId"/>
   </set>
</class>

<class name="Server" table="serverName">
  <id name="serverId" column="serverId">
   ...
  </id>
  <set name="users" table="server" inverse="true">
     <key column="serverId" not-null="true"/>
     <many-to-many class="User" column="uid"/>
  </set>
</class>

If you actually want a one-to-many relationship from serverName to users, but with a join table (server), then you can convert this mapping with help from the ref docs section 7.5.1.

MichaelNorman · **Joined:** Thu Aug 17, 2006 5:43 pm **Posts:** 2

Thanks for your help, you set me on the right track! But how would I solve this if I don't want to have a many-to-many relationship from User to Server. Say my classes look like this:

Code:

class User {
   Long uid;
   Server server;
}
class Server {
  Long serverId;
  String serverName;
}

So I don't want to use a set to store the association between user and server. This is because each user must have only one server. Is one-to-one the right decision? I am rather stuck here.

Thanks again for your help

greetings

norman

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Not one-to-one, probably. Unidirectional many-to-one would be better. Or even bidirectional one-to-many, if you want servers to know what users use them. Then you could have

Code:

class Server {
  Long serverId;
  String serverName
  Set<User> currentUsers;
}

Whether or not you want servers to know about users, you almost certainly want a many-to-one from User to Server.