Hibernate
/
hibernate-orm
mirror of https://github.com/hibernate/hibernate-orm
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

minor changes to inheritance 

git-svn-id: https://svn.jboss.org/repos/hibernate/trunk/Hibernate3/doc@4415 1b8cb986-b30d-0410-93ca-fae66ebed9b2
This commit is contained in:
Gavin King 2004-08-22 11:19:13 +00:00
parent a562acbbde
commit 1bd5301128
1 changed files with 15 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
reference/en/modules/inheritance_mapping.xml
View File

@ -243,41 +243,10 @@
<title>Limitations</title>
<para>
TODO: This section needs to be rewritten, Hibernate3 has almost no limitations on inheritance mappings
</para>
<para>
Hibernate assumes that an association maps to exactly one foreign key column.
Multiple associations per foreign key are tolerated (you might need to specify
<literal>inverse="true"</literal> or <literal>insert="false" update="false"</literal>),
but there is no way to map any association to multiple foreign keys. This means that:
</para>
<itemizedlist>
<listitem>
<para>
when an association is modified, it is always the same foreign key that is
updated
</para>
</listitem>
<listitem>
<para>
when an association is fetched lazily, a single database query is used
</para>
</listitem>
<listitem>
<para>
when an association is fetched eagerly, it may be fetched using a single
outer join
</para>
</listitem>
</itemizedlist>
<para>
In particular, it implies that polymorphic one-to-many associations to
classes mapped using the table-per-concrete-class strategy are
<emphasis>not supported</emphasis>. (Fetching this association would
require multiple queries or multiple joins.)
There are certain limitations to the "implicit polymorphism" approach to
the table-per-concrete-class mapping strategy. There are somewhat less
restrictive limitations to <literal>&lt;union-subclass&gt;</literal>
mappings. (TODO)
</para>
<para>
@ -343,6 +312,17 @@
<entry><emphasis>not supported</emphasis></entry>
<entry><emphasis>not supported</emphasis></entry>
</row>
<row>
<entry>table-per-concrete-class (union-subclass)</entry>
<entry><literal>??</literal></entry>
<entry><emphasis>??</emphasis></entry>
<entry><emphasis>&lt;one-to-many&gt; (<literal>inverse="true"</literal> only)</emphasis></entry>
<entry><literal>??</literal></entry>
<entry><emphasis>s.get(Payment.class, id)</emphasis></entry>
<entry><literal>from Payment p</literal></entry>
<entry><literal>from Order o join o.payment p</literal></entry>
<entry><emphasis>supported</emphasis></entry>
</row>
</tbody>
</tgroup>
</table>