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ianzabel
 Post subject: Many-to-many Map help.. frustrated beginner
PostPosted: Wed Aug 25, 2004 11:04 pm 
Newbie

Joined: Wed Aug 25, 2004 10:43 pm
Posts: 14
Location: NJ
I'm trying to map a many-to-many collection of Group objects into a Map on my User object, keyed by group name with values of Group object. Seems I can't get the mapping correct.

My table structure is like this:

USERS -> user_id
GROUP_MAP -> user_id, group_id (composite PK, both FKs)
GROUPS -> group_id

So, I have a table for users, and a table for groups, and they're mapped together using the group_map table.

I got it working fine as a set, using this mapping:
Code:
        <set name="groups" table="group_map" inverse="false" lazy="true">
            <key column="user_id"/>
            <many-to-many class="com.ezabel.core.user.Group" column="group_id"/>
        </set>


But, I'm unsuccessful getting it to work as a map. Again, I'd like the group.name column to be the key in the map, and the Group object the value.

Any idea what I'm doing wrong? Info posted below..

Thanks,
Ian.

Hibernate version:
Hibernate 2.1.6

Mapping documents:
Code:
<class name="com.ezabel.core.user.User" table="users">
        <id name="id" type="string" unsaved-value="null" column="user_id">
            <generator class="native"/>
        </id>

        <map name="groups" table="group_map" inverse="false" lazy="true">
            <key column="user_id"/>
            <index type="string" column="name"/>
            <many-to-many class="com.ezabel.core.user.Group" column="group_id"/>
        </map>
    </class>

    <class name="com.ezabel.core.user.Group" table="groups">
        <id name="id" type="int" column="group_id" unsaved-value="-1">
            <generator class="native"/>
        </id>
        <property name="name" column="name" type="string"/>
        <property name="description" column="description" type="string"/>
        <property name="active" column="active" type="boolean"/>
    </class>


Code between sessionFactory.openSession() and session.close():
Code:
user = (User)session.load( User.class, userId );
Hibernate.initialize( user.getGroups() );


Full stack trace of any exception that occurs:

Code:
java.sql.SQLException: Column not found,  message from server: "Unknown column 'groups0_.name' in 'field list'"
   at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:1977)
   at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1163)
   at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1272)
   at com.mysql.jdbc.Connection.execSQL(Connection.java:2236)
   at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1555)
   at org.apache.commons.dbcp.DelegatingPreparedStatement.executeQuery(DelegatingPreparedStatement.java:92)
   at net.sf.hibernate.impl.BatcherImpl.getResultSet(BatcherImpl.java:87)
   at net.sf.hibernate.loader.Loader.getResultSet(Loader.java:875)
   at net.sf.hibernate.loader.Loader.doQuery(Loader.java:269)
   at net.sf.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:133)
   at net.sf.hibernate.loader.Loader.loadCollection(Loader.java:990)

Name and version of the database you are using:
MySQL 4.0.16

Debug level Hibernate log excerpt:

Code:
Hibernate: select user0_.user_id as user_id0_ from users user0_ where user0_.user_id=?
Hibernate: select groups0_.user_id as user_id__, groups0_.group_id as group_id__, groups0_.name as name__, group1_.group_id as group_id0_, group1_.name as name0_, group1_.description as descript3_0_, group1_.active as active0_ from [b]group_map groups0_[/b] inner join groups group1_ on groups0_.group_id=group1_.group_id where groups0_.user_id=?
2004-08-25 22:58:17,703 WARN [net.sf.hibernate.util.JDBCExceptionReporter] - <SQL Error: 1054, SQLState: S0022>
2004-08-25 22:58:17,703 ERROR [net.sf.hibernate.util.JDBCExceptionReporter] - <Column not found,  message from server: "Unknown column 'groups0_.name' in 'field list'">
2004-08-25 22:58:17,734 WARN [net.sf.hibernate.util.JDBCExceptionReporter] - <SQL Error: 1054, SQLState: S0022>
2004-08-25 22:58:17,734 ERROR [net.sf.hibernate.util.JDBCExceptionReporter] - <Column not found,  message from server: "Unknown column 'groups0_.name' in 'field list'">
2004-08-25 22:58:17,734 ERROR [net.sf.hibernate.util.JDBCExceptionReporter] - <could not initialize collection: [com.ezabel.core.user.User.groups#iwz]>
Code:
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gavin
 Post subject:
PostPosted: Wed Aug 25, 2004 11:29 pm 
Hibernate Team
Hibernate Team

Joined: Tue Aug 26, 2003 12:50 pm
Posts: 5130
Location: Melbourne, Australia
This is not possible for a many-to-many association.

However, if you want to submit a feature rquest, I guess its something we could give some thought to.
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ianzabel
 Post subject:
PostPosted: Wed Aug 25, 2004 11:34 pm 
Newbie

Joined: Wed Aug 25, 2004 10:43 pm
Posts: 14
Location: NJ
gavin wrote:
This is not possible for a many-to-many association.

However, if you want to submit a feature rquest, I guess its something we could give some thought to.


Oh, haha, I hadn't expected that answer! Nice. Well, at least it wasn't something I was doing wrong, eh? ;)

How would I go about submitting a feature request?
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gavin
 Post subject:
PostPosted: Wed Aug 25, 2004 11:57 pm 
Hibernate Team
Hibernate Team

Joined: Tue Aug 26, 2003 12:50 pm
Posts: 5130
Location: Melbourne, Australia
JIRA.

Not promising anything, by the way.
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StevenCason
 Post subject:
PostPosted: Tue Sep 14, 2004 5:16 pm 
Newbie

Joined: Tue Sep 14, 2004 5:01 pm
Posts: 2
Location: Baltimore, Maryland, USA
Gavin,

Can you unpack for me a little bit what you mean by "not possible for a many-to-many association"? I'm trying to do something similar, except that I want the Map key to be the same column as that specified in the many-to-many tag, as follows.

<class
name="Worker"
table="WORKER"

batch-size="1"
dynamic-insert="true"
dynamic-update="true"
lazy="false"
mutable="true"
optimistic-lock="version"
polymorphism="implicit"
>
<composite-id
access="property"
name="id"
class="WorkerID"
>
<key-property name="cossn" type="string" column="COSSN" />
<key-property name="cid" type="string" column="CID" />
</composite-id>

<timestamp
name="lastModTs"
column="LASTMOD_TS"
access="property"
unsaved-value="null"
/>


<map
name="employers"
table="WRKREMPLYR"
lazy="false"
cascade="all"
access="property"
>
<key>
<column name="COSSN" />
<column name="CID" />
</key>
<index column="EMPLOYER_ID" type="string"/>
<many-to-many class="Employer" column="EMPLOYER_ID" />
</map>

My database contains tables for WORKERS and EMPLOYERS. The many-to-many association between those two relations is realized by the table WRKREMPLYRS, which consists solely of the key columns of both tables.

When my app find()s a Worker, I need it to also retrieve all the Employers associated with that Worker, and place them in a java.util.Map named 'employers', which is a property of the Worker class. I need the Map to be indexed by the EMPLOYER_ID column, which is a UUID string generated by Hibernate and is the primary key of the EMPLOYERS table.

You see why I ask. Is this whole class of mapping objectives impossible in Hibernate, or is it more narrowly impossible to map a many-to-many association indexing on a value that's not the primary key of the collected entity?

Thanks in advance,
Steven
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victorstar
 Post subject:
PostPosted: Fri Sep 17, 2004 3:42 pm 
Newbie

Joined: Tue Apr 20, 2004 4:23 pm
Posts: 5
I've also just ran across the problem mentioned in the original message: need to map many-to-many assosiation with collection index field that's the same as many-to-many key column....

If there is a feature request I'd like to second that.
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RobJellinghaus
 Post subject:
PostPosted: Thu Mar 17, 2005 4:40 pm 
Expert
Expert

Joined: Thu Jan 08, 2004 6:17 pm
Posts: 278
I just posted such a feature request: http://opensource.atlassian.com/projects/hibernate/browse/HHH-250

See also my thread on a related issue: http://forum.hibernate.org/viewtopic.php?t=940128
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tomwilsonfl
 Post subject:
PostPosted: Thu Jan 31, 2008 12:13 am 
Newbie

Joined: Wed Jan 30, 2008 11:59 pm
Posts: 2
I am also looking to do this exact thing, but 3 1/2 years later. :)

I wish for my Map "members" in my Group class to have (type Long - FK from association table) memberId as a key and a Member class as value.

I have achieved this with a one-to-many Map, but this is a many-to-many. I see in the documentation there is a <map-key-many-to-many/> but it is hard for me to understand the usage of it.

Is this usage possible now in Hibernate 3.2.5?

Thanks,
Tom :)
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anirelles
 Post subject:
PostPosted: Tue May 27, 2008 5:02 am 
Newbie

Joined: Tue May 27, 2008 4:58 am
Posts: 1
same thing for me
I'm struggling to make it work.

Please someone can help?
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pghosh
 Post subject: Re: Many-to-many Map help.. frustrated beginner [solution]
PostPosted: Wed Feb 17, 2010 5:49 pm 
Newbie

Joined: Wed Feb 17, 2010 5:43 pm
Posts: 1
Here is another solution using the formula attribute of <map-key>

In this example foo has a many-to-many relationship with bar via foo_has_bar.

Code:
foo          foo_has_bar     bar
foo_id <--    foo_id      --> bar_id
                  bar_id

<hibernate-mapping>
    <class name="Bar" table="bar" catalog="mydb">
        <id name="id" type="java.lang.Integer">
            <column name="bar_id" />
            <generator class="identity" />
        </id>
    </class>
    <class name="Foo" table="foo" catalog="mydb">
        <id name="id" type="java.lang.Integer">
            <column name="foo_id" />
            <generator class="identity" />
        </id>
        <map name="bars" inverse="true" cascade="all" table="foo_bar_x">
            <key column="foo_id" not-null="true" />
            <map-key type="int" formula="bar_id"/>
            <many-to-many column="bar_id" class="Bar"/>
        </map>
    </class>
</hibernate-mapping>
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