docs/2.0/dataobjects-example.html

Title: DataObjects Example

	
<P>As discussed in <A href="dataobjects.html" title="DataObjects">DataContext</A> chapter, any changes made to the DataObjects via &quot;set*&quot; methods are synchronized with the database by calling <TT>DataContext.commitChanges</TT>. Here is an example showing how the <TT>Painting</TT> object is fetched, modified and saved back. The following modifications are performed: the price of the first retrieved painting is doubled, a new painting is added that belongs to the same artist as the painting fetched before:</P>
<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
<PRE class="code-java"><SPAN class="code-keyword">import</SPAN> java.math.BigDecimal;
<SPAN class="code-keyword">import</SPAN> java.util.List;
<SPAN class="code-keyword">import</SPAN> org.apache.cayenne.access.DataContext;
<SPAN class="code-keyword">import</SPAN> org.apache.cayenne.query.SelectQuery;
<SPAN class="code-keyword">import</SPAN> org.apache.cayenne.exp.Expression;
<SPAN class="code-keyword">import</SPAN> org.apache.cayenne.exp.ExpressionFactory;
<SPAN class="code-keyword">import</SPAN> org.apache.art.Painting;
<SPAN class="code-keyword">import</SPAN> org.apache.art.Artist;
...

<SPAN class="code-comment">// assume <SPAN class="code-keyword">this</SPAN> exists and initialized
</SPAN>DataContext ctxt;
...
Expression e =
  ExpressionFactory.greaterExp(<SPAN class="code-quote">&quot;estimatedPrice&quot;</SPAN>,
                        <SPAN class="code-keyword">new</SPAN> BigDecimal(100000.0));
SelectQuery q = <SPAN class="code-keyword">new</SPAN> SelectQuery(Painting.class, e);
List realExpensiveArt = ctxt.performQuery(q);

<SPAN class="code-keyword">if</SPAN>(realExpensiveArt.size() &gt; 0) {
  Painting firstPainting = (Painting)realExpensiveArt.get(0);

  <SPAN class="code-comment">// <SPAN class="code-object">double</SPAN> the price
</SPAN>  <SPAN class="code-object">double</SPAN> oldPrice = firstPainting.getEstimatedPrice().doubleValue();
  firstPainting.setEstimatedPrice(<SPAN class="code-keyword">new</SPAN> BigDecimal(oldPrice * 2.00));

  <SPAN class="code-comment">// create <SPAN class="code-keyword">new</SPAN> painting and register it with DataContext
</SPAN>  <SPAN class="code-comment">// <SPAN class="code-quote">&quot;Painting&quot;</SPAN> string is a name of ObjEntity in the DataMap
</SPAN>  Painting newPainting = (Painting)ctxt.newObject(Painting.class);
  newPainting.setPaintingTitle(<SPAN class="code-quote">&quot;Sunset as it is&quot;</SPAN>);

  <SPAN class="code-comment">// price it as unreasonable as other paintings
</SPAN>  newPainting.setEstimatedPrice(<SPAN class="code-keyword">new</SPAN> BigDecimal(5000000.0));

  <SPAN class="code-comment">// get artist via relationship
</SPAN>  Artist artist = firstPainting.getToArtist();

  <SPAN class="code-comment">// assign <SPAN class="code-keyword">new</SPAN> painting to an artist
</SPAN>  artist.addToPaintingArray(newPainting);

  <SPAN class="code-comment">// save all the changes we've made so far
</SPAN>  ctxt.commitChanges();
}
...
</PRE>
</DIV></DIV>
<P>If SQL tracing is turned on, and depending on the preexisting data in the database, the following SQL statements might be printed to console during the commit phase:</P>
<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent">
<PRE>[main 12-22 15:50:19] QueryLogger: --- will run 2 queries.
[main 12-22 15:50:19] QueryLogger: INSERT INTO PAINTING (PAINTING_ID, PAINTING_TITLE, ESTIMATED_PRICE,
 ARTIST_ID) VALUES (?, ?, ?, ?) [params: 200, 'Sunset as it is', 5000000, 10]
[main 12-22 15:50:19] QueryLogger: === updated 1 row.
[main 12-22 15:50:19] QueryLogger: UPDATE PAINTING SET ESTIMATED_PRICE = ? WHERE PAINTING_ID = ? 
 [params: 2000000, 34]
[main 12-22 15:50:19] QueryLogger: === updated 1 row.
[main 12-22 15:50:19] QueryLogger: +++ transaction committed.
</PRE>
</DIV></DIV>