<html><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>How to cascade deletion</title><link href="default.css" rel="stylesheet"></head><body marginwidth="0" marginheight="0" leftmargin="0" bottommargin="0" topmargin="0" vlink="#6763a9" link="#6763a9" bgcolor="#ffffff"><a name="top"></a><table height="400" cellspacing="0" cellpadding="0" border="0"><tr><td bgcolor="#7270c2" align="left" valign="top" width="10"><img border="0" height="1" width="1" src="images/dotTrans.gif"></td><td bgcolor="#7270c2" align="left" valign="top" width="150"><img border="0" height="1" width="1" src="images/dotTrans.gif"></td><td align="left" valign="top" width="7"><img height="1" width="1" border="0" src="images/dotTrans.gif"></td><td align="left" valign="top" width="70"><img border="0" height="6" width="70" src="images/dotTrans.gif"></td><td align="left" valign="top" width="100%"><img border="0" height="6" width="100%" src="images/top_2.gif"></td></tr><tr><td align="left" valign="top" bgcolor="#7270c2" width="10"><img height="1" width="1" border="0" src="images/dotTrans.gif"></td><td align="left" valign="top" bgcolor="#7270c2" width="150"><img height="1" width="1" border="0" src="images/dotTrans.gif"></td><td align="left" valign="top" bgcolor="#ffffff" width="7"></td><td align="left" valign="top" width="70"><img border="0" height="1" width="1" src="images/dotTrans.gif"></td><td align="left" valign="middle" width="100%"><a href="license.html"><span class="menuTopOff">License</span></a> <a href="http://www.codehaus.org"><span class="menuTopOff">Codehaus</span></a> <a href="http://openejb.org"><span class="menuTopOff">OpenEJB</span></a> <a href="http://openjms.sf.net"><span class="menuTopOff">OpenJMS</span></a> <a href="http://openorb.sf.net"><span class="menuTopOn">OpenORB</span></a> <a href="http://tyrex.sf.net"><span class="menuTopOff">Tyrex</span></a> <br><img border="0" height="2" width="1" src="images/dotTrans.gif"></td></tr><tr><td align="left" valign="top" bgcolor="#7270c2" width="10"><img border="0" height="3" width="10" src="images/dotTrans.gif"></td><td align="right" valign="top" bgcolor="#7270c2" width="150"><img border="0" height="3" width="105" src="images/line_sm.gif"></td><td align="left" valign="top" bgcolor="#a9a5de" width="7"><img border="0" height="3" width="7" src="images/line_sm.gif"></td><td align="left" valign="top" width="70"><img border="0" height="3" width="70" src="images/line_light.gif"></td><td align="left" valign="top" width="100%"><img border="0" height="3" width="100%" src="images/line_light.gif"></td></tr><tr><td align="left" valign="top" bgcolor="#7270c2"><img border="0" height="10" width="10" src="images/dotTrans.gif"></td><td align="left" valign="top" bgcolor="#7270c2" width="150"><img border="0" height="2" width="1" src="images/dotTrans.gif"><br><table cellspacing="0" cellpadding="10" border="0"><tr><td><script src="http://www.ohloh.net/p/3635/widgets/project_users_logo.js" type="text/javascript"></script></td></tr></table><table cellspacing="0" cellpadding="0" border="0"><tr><td align="left" valign="top"><span class="subMenuOn">Old releases</span></td></tr><tr><td align="left" valign="top">
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<a href="origins.html"><span class="subMenuOff">Project Name</span></a></td></tr></table><br></td><td align="left" valign="top" bgcolor="#a9a5de" width="7"> </td><td align="left" valign="top" width="70"> </td><td valign="top" width="100%" rowspan="4"><table width="100%" cellspacing="0" cellpadding="0" border="0" rows="2" cols="2"><tr><td align="left" valign="top"><br><img width="115" vspace="0" src="images/castor.gif" hspace="0" height="34" border="0"><br><img src="images/dotTrans.gif" hspace="0" height="10" border="0"></td><td align="right" valign="top" height="5" width="120"></td></tr></table><p></p><p></p><br><h2 align="center">How to cascade deletion</h2><HR size="1"><span class="bodyGrey"><b><a href="#Overview">Overview</a></b><br></span><span class="bodyGrey"><b><a href="#Enabling-cascading-deletion">Enabling cascading deletion</a></b><br></span><span class="bodyGrey"><b><a href="#Scenarios">Scenarios</a></b><br></span><span class="bodyGrey"><a href="#db.remove()"> db.remove()</a><br></span><span class="bodyGrey"><b><a href="#See-also">See also</a></b><br></span><HR size="1"><br><a name="Overview"><h2>Overview</h2></a>
<p><span class="bodyGrey">If you enable cascading deletion on a relationship, deleting the object on one end of the relationship
(i.e. calling db.remove() on the object) will also delete the object on the other end.</span></p>
<a name="Enabling-cascading-deletion"><h2>Enabling cascading deletion</h2></a>
<p><span class="bodyGrey">To enable cascading deletion on a relationship you simply set the cascading attribute of the <sql> field
describing the relation to "delete" (or "all"):</span></p>
<p></p><table bgcolor="#7270c2" cellpadding="1" cellspacing="1" border="0" width="100%"><tr><td><table bgcolor="#ededed" cellpadding="4" cellspacing="1" border="0" width="100%"><tr><td><span class="bodyBlack"><pre>
<field name="book" type="myapp.Book" >
<sql name="book_id" cascading="delete" />
</field>
</pre></span></td></tr></table></td></tr></table><p></p>
<p><span class="bodyGrey">In case of bidirectional relationships, be aware that it matters on which end you enable cascading deletion.
It is also possible to enable it on both ends.</span></p>
<a name="Scenarios"><h2>Scenarios</h2></a>
<p><span class="bodyGrey"></span></p>
<a name="db.remove()"><h3>db.remove()</h3></a>
<p><span class="bodyGrey">Let's say we have the objects Author and Book and they are in a one-to-one relationship, with every Book
having exactly one Author. The database looks like this:</span></p>
<table border="0" cellspacing="0" cellpadding="2" bgcolor="#7270c2" style="display:inline">
<tr bgcolor="#ffffff">
<th>Author</th>
</tr>
<tr>
<td><span class="bodyGrey">
<table border="0" cellspacing="0" cellpadding="6" bgcolor="#ededed">
<tr bgcolor="#7270c2" style="color:#000000">
<th align="left">id</th>
<th align="left">name</th>
</tr>
<tr bgcolor="#DEDEDE">
<td><span class="bodyGrey">1</span></td>
<td><span class="bodyGrey">"John Jackson"</span></td>
</tr>
</table>
</span></td>
</tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" bgcolor="#7270c2" style="display:inline">
<tr bgcolor="#ffffff">
<th>Book</th>
</tr>
<tr>
<td><span class="bodyGrey">
<table border="0" cellspacing="0" cellpadding="6" bgcolor="#ededed">
<tr bgcolor="#7270c2" style="color:#000000">
<th align="left">id</th>
<th align="left">title</th>
<th align="left">author_id</th>
</tr>
<tr bgcolor="#DEDEDE">
<td><span class="bodyGrey">1</span></td>
<td><span class="bodyGrey">"My Life"</span></td>
<td><span class="bodyGrey">1</span></td>
</tr>
</table>
</span></td>
</tr>
</table>
<p><span class="bodyGrey">Now, since we specified the relationship to cascade deletion, if we remove the book,
the author gets removed too (after all, an author without a book isn't really an author).</span></p>
<p></p><table bgcolor="#7270c2" cellpadding="1" cellspacing="1" border="0" width="100%"><tr><td><table bgcolor="#ededed" cellpadding="4" cellspacing="1" border="0" width="100%"><tr><td><span class="bodyBlack"><pre>
db.begin();
Book b1 = db.load(Book.class, 1);
db.remove(db1);
db.commit();</pre></span></td></tr></table></td></tr></table><p></p>
<p><span class="bodyGrey">Afterwards, the database predictably looks like this:</span></p>
<table border="0" cellspacing="0" cellpadding="2" bgcolor="#7270c2" style="display:inline">
<tr bgcolor="#ffffff">
<th>Author</th>
</tr>
<tr>
<td><span class="bodyGrey">
<table border="0" cellspacing="0" cellpadding="6" bgcolor="#ededed">
<tr bgcolor="#7270c2" style="color:#000000">
<th align="left">id</th>
<th align="left">name</th>
</tr>
<tr bgcolor="#DEDEDE">
<td colspan="2"><span class="bodyGrey" colspan="2">(empty table)</span></td>
</tr>
</table>
</span></td>
</tr>
</table>
<table border="0" cellspacing="0" cellpadding="2" bgcolor="#7270c2" style="display:inline">
<tr bgcolor="#ffffff">
<th>Book</th>
</tr>
<tr>
<td><span class="bodyGrey">
<table border="0" cellspacing="0" cellpadding="6" bgcolor="#ededed">
<tr bgcolor="#7270c2" style="color:#000000">
<th align="left">id</th>
<th align="left">title</th>
<th align="left">author_id</th>
</tr>
<tr bgcolor="#DEDEDE">
<td colspan="3"><span class="bodyGrey" colspan="3">(empty table)</span></td>
</tr>
</table>
</span></td>
</tr>
</table>
<p><span class="bodyGrey">Cascading the deletion of objects in to-many relationships works in exactly the same way.</span></p>
<p><span class="bodyGrey">Note: You need to explicitly invoke db.remove() to delete an object. Simply setting a relational property to NULL
or removing an item from a collection will not remove the corresponding entity from the database, even with cascading
deletion enabled.</span></p>
<a name="See-also"><h2>See also</h2></a>
<table cellspacing="2" cellpadding="2" border="0"><tr><td height="5" colspan="2"></td></tr><span class="bodyGrey">
<tr><td width="10" valign="top" align="left">-</td><td valign="top" align="left"><span class="bodyGrey">
<a href="how-to-use-cascading-operations.html">How to use cascading operations - overview</a>
</span></td></tr>
</span></table>
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