| <html><head> |
| <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> |
| <title xmlns:d="http://docbook.org/ns/docbook">Chapter 8. Deleting Objects</title><link rel="stylesheet" type="text/css" href="css/cayenne-doc.css"><meta xmlns:d="http://docbook.org/ns/docbook" name="keywords" content="Cayenne 3.1 documentation"><meta xmlns:d="http://docbook.org/ns/docbook" name="description" content="User documentation for Apache Cayenne version 3.1"><link rel="home" href="index.html" title="Getting Started with Cayenne"><link rel="up" href="getting-started-part3.html" title="Part III. Learning Cayenne API"><link rel="prev" href="ch07.html" title="Chapter 7. Selecting Objects"><link rel="next" href="getting-started-part4.html" title="Part IV. Converting to Web Application"><script xmlns:d="http://docbook.org/ns/docbook" type="text/javascript"> |
| var _gaq = _gaq || []; |
| _gaq.push(['_setAccount', 'UA-7036673-1']); |
| _gaq.push(['_trackPageview']); |
| (function() { |
| var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; |
| ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; |
| var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); |
| })(); |
| </script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div xmlns:d="http://docbook.org/ns/docbook" class="navheader"><table width="100%" summary="Navigation header"><tr><th class="versioninfo">v.3.1 (3.1)</th><th align="center">Chapter 8. Deleting Objects</th><th></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch07.html">Prev</a> </td><th width="60%" align="center"><a accesskey="u" href="getting-started-part3.html">Part III. Learning Cayenne API</a></th><td width="20%" align="right"> <a accesskey="n" href="getting-started-part4.html">Next</a></td></tr></table><hr></div><div class="chapter" title="Chapter 8. Deleting Objects"><div class="titlepage"><div><div><h2 class="title"><a name="d0e444"></a>Chapter 8. Deleting Objects</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="ch08.html#setup-delete-rules">Setting Up Delete Rules</a></span></dt><dt><span class="section"><a href="ch08.html#deleting-objects">Deleting Objects</a></span></dt></dl></div><p>This chapter explains how to model relationship delete rules and how to delete individual |
| objects as well as sets of objects. Also demonstrated the use of Cayenne class to run a |
| query.</p><div class="section" title="Setting Up Delete Rules"><div class="titlepage"><div><div><h2 class="title"><a name="setup-delete-rules"></a>Setting Up Delete Rules</h2></div></div></div><p>Before we discuss the API for object deletion, lets go back to CayenneModeler and set |
| up some delete rules. Doing this is optional but will simplify correct handling of the |
| objects related to deleted objects.</p><p>In the Modeler go to "Artist" ObjEntity, "Relationships" tab and select "Cascade" for |
| the "paintings" relationship delete rule:</p><p><span class="inlinemediaobject"><img src="images/modeler-deleterule.png"></span> |
| </p><p>Repeat this step for other relationships:</p><div class="itemizedlist"><ul class="itemizedlist"><li class="listitem"><p>For Gallery set "paintings" relationship to be "Nullify", as a painting can |
| exist without being displayed in a gallery.</p></li><li class="listitem"><p>For Painting et both relationships rules to "Nullify".</p></li></ul></div><p>Now save the mapping, and refresh the project in Eclispe.</p></div><div class="section" title="Deleting Objects"><div class="titlepage"><div><div><h2 class="title"><a name="deleting-objects"></a>Deleting Objects</h2></div></div></div><p>While deleting objects is possible via SQL, qualifying a delete on one or more IDs, a |
| more common way in Cayenne (or ORM in general) is to get a hold of the object first, and |
| then delete it via the context. Let's use utility class Cayenne to find an |
| artist:</p><pre class="programlisting">Expression qualifier = ExpressionFactory.matchExp(Artist.NAME_PROPERTY, <span xmlns="http://www.w3.org/1999/xhtml" class="hl-string">"Pablo Picasso"</span>); |
| SelectQuery select = <span xmlns="http://www.w3.org/1999/xhtml" class="hl-keyword">new</span> SelectQuery(Artist.<span xmlns="http://www.w3.org/1999/xhtml" class="hl-keyword">class</span>, qualifier); |
| Artist picasso = (Artist) Cayenne.objectForQuery(context, select);</pre><p>Now let's delete the artist:</p><pre class="programlisting"><span xmlns="http://www.w3.org/1999/xhtml" class="hl-keyword">if</span> (picasso != null) { |
| context.deleteObject(picasso); |
| context.commitChanges(); |
| }</pre><p>Since we set up "Cascade" delete rule for the Artist.paintings relationships, Cayenne |
| will automatically delete all paintings of this artist. So when your run the app you'll |
| see this output:</p><pre class="programlisting">INFO: SELECT t0.DATE_OF_BIRTH, t0.NAME, t0.ID FROM ARTIST t0 |
| WHERE t0.NAME = ? [bind: 1->NAME:'Pablo Picasso'] - prepared in 6 ms. |
| INFO: === returned 1 row. - took 18 ms. |
| INFO: +++ transaction committed. |
| INFO: --- transaction started. |
| INFO: DELETE FROM PAINTING WHERE ID = ? |
| INFO: [batch bind: 1->ID:200] |
| INFO: [batch bind: 1->ID:201] |
| INFO: === updated 2 rows. |
| INFO: DELETE FROM ARTIST WHERE ID = ? |
| INFO: [batch bind: 1->ID:200] |
| INFO: === updated 1 row. |
| INFO: +++ transaction committed.</pre></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch07.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="getting-started-part3.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="getting-started-part4.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 7. Selecting Objects </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Part IV. Converting to Web Application</td></tr></table></div></body></html> |
