One-to-many list mapping question

nickwest · **Joined:** Mon May 02, 2005 3:32 am **Posts:** 1

Hi,

I'm rather new to Hibernate so please bare with me.

I have a User class with a collection of Group objects in it. In the database I have a USER table, a GROUP table and a USER_GROUP table defining which groups are associated with which user. This all worked using OJB, however I don't understand how to configure the <list> mapping for Hibernate. I've placed below example code, db schemas and the mappings, can somebody tell me how I should write this <list> mapping please? My version below just doesn't work!

The Java

Code:

public class User
{
    private Collection groups;
...
}

public class Group
{
...
}

The DB Schema

Code:

CREATE TABLE USER(
 ID     INT NOT NULL,
 ...
);

CREATE TABLE GROUP(
 ID     INT NOT NULL,
 ...
);

CREATE TABLE USER_GROUP(
    USER_ID     INT(11),
    GROUP_ID    INT(11)
);

The Mappings

Code:

<class name="Group" table="GROUP">
    <id name="id"
        type="integer"
        column="ID">
        <generator class="assigned"/>
    </id>
...
</class>

<class name="User" table="USER"
    >
    <id name="id"
        type="integer"
        unsaved-value="null"
        column="ID">
        <generator class="assigned"/>
    </id>

...
   <list name="groups"
        table="USER_GROUP"
        inverse="true"
        lazy="true">
        <key column="USER_ID"/>
        <one-to-many
            column="GROUP_ID"
            class="Group"
        />
    </list>
</class>

anthony · **Posted:** Mon May 02, 2005 3:59 am

hi,
change

Code:

   <list name="groups" 
        table="USER_GROUP" 
        inverse="true" 
        lazy="true"> 
        <key column="USER_ID"/> 
        <one-to-many 
            column="GROUP_ID" 
            class="Group" 
        /> 
    </list> 

to

Code:

   <bag name="groups" 
        table="USER_GROUP" 
        inverse="true" 
        lazy="true"> 
        <key column="USER_ID"/> 
        <one-to-many 
            column="GROUP_ID" 
            class="Group" 
        /> 
    </bag> 

if you don't have an index column.
(no change in your java code)

You should read the reference guide about different collection mapping.