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POMultiple relationships with single mapping table without generating foreign keys by Hibernate
 

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    <p>I have <strong>two base abstract classes</strong> and there are multiple additional classes derived from these two, adding additional attributes etc.</p> <p>There exist relations between those specific derived types.</p> <p><strong>A simple illustrating example:</strong></p> <p><code>Role</code> and <code>Group</code> classes are <code>abstract</code>, but they are not marked as <code>@MappedSuperclass</code>. </p> <p><code>InheritanceType.JOINED</code> strategy is being used, so both tables <code>Role</code> (for abstract class) and <code>AdminRole</code> (for derived class) should exist (they both will have the same <code>RoleID</code>).</p> <ul> <li><code>DiscussionGroup</code> has one <code>AdminRole</code> property, a <code>Set&lt;DiscussantRole&gt;</code>, a <code>Set&lt;ManagerRole&gt;</code> </li> <li><code>WorkingGroup</code> has <code>Set&lt;WorkerRole&gt;</code>, <code>Set&lt;ManagerRole&gt;</code></li> </ul> <blockquote> <pre><code>Role |-- AdminRole |-- DiscussantRole |-- ManagerRole |-- WorkerRole Group |-- DiscussionGroup |-- WorkingGroup </code></pre> </blockquote> <p>Because the number of derived classes can grow, and because classes derived from Role can have relations to different classes derived from Group (and vice versa) this would lead to a large amount of different mapping tables (Worker_DiscussionGroup, Worker_WorkingGroup) or multiple foreign key columns (in M:1 relationships - e.g. a ManagerRole would have to have DiscussionGroupID and WorkingGroupId). <strong>I want to map all these relations through one common mapping table.</strong></p> <pre><code>Role_Group (RoleID, GroupId) </code></pre> <p>We use <strong>Hibernate to generate the DDL schema (hbm2ddl.auto=create)</strong> during current development (we will use a static schema definition for later production use). Hibernate automatically creates Foreign keys for the relations, and thats quite good for us. </p> <p>If I instruct it to use the same mapping a table for joins (for the many-to-many, many-to-many and for one-to-one as well), <strong>it will try to create foreign keys</strong> as well. And it is of course not possible to create a foreign key on <code>RoleID</code> from <code>Role_Group</code> to <code>AdminRole</code> and <code>DiscussantRole</code> at the same time, so I get an error.</p> <p><strong>Is there any way, how to instruct Hibernate</strong></p> <ol> <li><p><strong>to generate selected relationships without foreign keys</strong></p> <p>or </p></li> <li><p><strong>to define that the relation should be based on the abstract ancestors (i.e. DiscussionGroup and its Set should be mapped as 1:N - Group and Set)?</strong></p></li> </ol>
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