| <html><head> |
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| <title>3. Lifecycle Examples</title><link rel="stylesheet" href="css/docbook.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.72.0"><link rel="start" href="manual.html" title="Apache OpenJPA User's Guide"><link rel="up" href="jpa_overview_em.html" title="Chapter 8. EntityManager"><link rel="prev" href="jpa_overview_em_lifecycle.html" title="2. Entity Lifecycle Management"><link rel="next" href="jpa_overview_em_identity.html" title="4. Entity Identity Management"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">3. |
| Lifecycle Examples |
| </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="jpa_overview_em_lifecycle.html">Prev</a> </td><th width="60%" align="center">Chapter 8. |
| EntityManager |
| </th><td width="20%" align="right"> <a accesskey="n" href="jpa_overview_em_identity.html">Next</a></td></tr></table><hr></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="jpa_overview_em_lifeexamples"></a>3. |
| Lifecycle Examples |
| </h2></div></div></div><p> |
| The examples below demonstrate how to use the lifecycle methods presented in the |
| previous section. The examples are appropriate for out-of-container use. Within |
| a container, <code class="classname"> EntityManager</code>s are usually injected, and |
| transactions are usually managed. You would therefore omit the <code class="methodname"> |
| createEntityManager</code> and <code class="methodname">close</code> calls, as |
| well as all transaction demarcation code. |
| </p><div class="example"><a name="jpa_overview_em_lifecycle_persist"></a><p class="title"><b>Example 8.1. |
| Persisting Objects |
| </b></p><div class="example-contents"><a class="indexterm" name="d0e4997"></a><pre class="programlisting"> |
| // create some objects |
| Magazine mag = new Magazine("1B78-YU9L", "JavaWorld"); |
| |
| Company pub = new Company("Weston House"); |
| pub.setRevenue(1750000D); |
| mag.setPublisher(pub); |
| pub.addMagazine(mag); |
| |
| Article art = new Article("JPA Rules!", "Transparent Object Persistence"); |
| art.addAuthor(new Author("Fred", "Hoyle")); |
| mag.addArticle(art); |
| |
| // persist |
| EntityManager em = emf.createEntityManager(); |
| em.getTransaction().begin(); |
| em.persist(mag); |
| em.persist(pub); |
| em.persist(art); |
| em.getTransaction().commit(); |
| |
| // or we could continue using the EntityManager... |
| em.close(); |
| </pre></div></div><br class="example-break"><div class="example"><a name="jpa_overview_em_lifecycle_update"></a><p class="title"><b>Example 8.2. |
| Updating Objects |
| </b></p><div class="example-contents"><a class="indexterm" name="d0e5009"></a><pre class="programlisting"> |
| Magazine.MagazineId mi = new Magazine.MagazineId(); |
| mi.isbn = "1B78-YU9L"; |
| mi.title = "JavaWorld"; |
| |
| // updates should always be made within transactions; note that |
| // there is no code explicitly linking the magazine or company |
| // with the transaction; JPA automatically tracks all changes |
| EntityManager em = emf.createEntityManager(); |
| em.getTransaction().begin(); |
| Magazine mag = em.find(Magazine.class, mi); |
| mag.setPrice(5.99); |
| Company pub = mag.getPublisher(); |
| pub.setRevenue(1750000D); |
| em.getTransaction().commit(); |
| |
| // or we could continue using the EntityManager... |
| em.close(); |
| </pre></div></div><br class="example-break"><div class="example"><a name="jpa_overview_em_lifecycle_delete"></a><p class="title"><b>Example 8.3. |
| Removing Objects |
| </b></p><div class="example-contents"><a class="indexterm" name="d0e5021"></a><pre class="programlisting"> |
| // assume we have an object id for the company whose subscriptions |
| // we want to delete |
| Object oid = ...; |
| |
| // deletes should always be made within transactions |
| EntityManager em = emf.createEntityManager(); |
| em.getTransaction().begin(); |
| Company pub = (Company) em.find(Company.class, oid); |
| for (Subscription sub : pub.getSubscriptions()) |
| em.remove(sub); |
| pub.getSubscriptions().clear(); |
| em.getTransaction().commit(); |
| |
| // or we could continue using the EntityManager... |
| em.close(); |
| </pre></div></div><br class="example-break"><div class="example"><a name="jpa_overview_em_detachex"></a><p class="title"><b>Example 8.4. |
| Detaching and Merging |
| </b></p><div class="example-contents"><p> |
| This example demonstrates a common client/server scenario. The client requests |
| objects and makes changes to them, while the server handles the object lookups |
| and transactions. |
| </p><pre class="programlisting"> |
| // CLIENT: |
| // requests an object with a given oid |
| Record detached = (Record) getFromServer(oid); |
| |
| ... |
| |
| // SERVER: |
| // send object to client; object detaches on EM close |
| Object oid = processClientRequest(); |
| EntityManager em = emf.createEntityManager(); |
| Record record = em.find(Record.class, oid); |
| em.close(); |
| sendToClient(record); |
| |
| ... |
| |
| // CLIENT: |
| // makes some modifications and sends back to server |
| detached.setSomeField("bar"); |
| sendToServer(detached); |
| |
| ... |
| |
| // SERVER: |
| // merges the instance and commit the changes |
| Record modified = (Record) processClientRequest(); |
| EntityManager em = emf.createEntityManager(); |
| em.getTransaction().begin(); |
| Record merged = (Record) em.merge(modified); |
| merged.setLastModified(System.currentTimeMillis()); |
| merged.setModifier(getClientIdentityCode()); |
| em.getTransaction().commit(); |
| em.close(); |
| </pre></div></div><br class="example-break"></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="jpa_overview_em_lifecycle.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="jpa_overview_em.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="jpa_overview_em_identity.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">2. |
| Entity Lifecycle Management |
| </td><td width="20%" align="center"><a accesskey="h" href="manual.html">Home</a></td><td width="40%" align="right" valign="top"> 4. |
| Entity Identity Management |
| </td></tr></table></div></body></html> |
