readSecondary.html [plain text]
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<th colspan="3" align="center">Reading Secondary Databases</th>
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<td width="20%" align="left"><a accesskey="p" href="secondaryProps.html">Prev</a> </td>
<th width="60%" align="center">Chapter 10. Secondary Databases</th>
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<h2 class="title" style="clear: both"><a id="readSecondary"></a>Reading Secondary Databases</h2>
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<p>
Like a primary database, you can read records from your secondary
database either by using the
<span>
<tt class="methodname">SecondaryDatabase.get()</tt> method,
</span>
or by using
<span>a <tt class="classname">SecondaryCursor</tt>.</span>
The main difference between reading secondary and primary databases is that when
you read a secondary database record, the secondary record's data is not
returned to you. Instead, the primary key and data corresponding to the
secondary key are returned to you.
</p>
<p>
For example, assuming your secondary database contains keys related
to a person's full name:
</p>
<a id="java_index6"></a>
<pre class="programlisting">package db.GettingStarted;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;
import com.sleepycat.db.SecondaryDatabase;
...
SecondaryDatabase mySecondaryDatabase = null;
try {
// Omitting all database opens
...
String searchName = "John Doe";
DatabaseEntry searchKey =
new DatabaseEntry(searchName.getBytes("UTF-8"));
DatabaseEntry primaryKey = new DatabaseEntry();
DatabaseEntry primaryData = new DatabaseEntry();
// Get the primary key and data for the user 'John Doe'.
OperationStatus retVal = mySecondaryDatabase.get(null, searchKey,
primaryKey,
primaryData,
LockMode.DEFAULT);
} catch (Exception e) {
// Exception handling goes here
}</pre>
<p>
Note that, just like
<span><tt class="methodname">Database.get()</tt>, </span>
if your secondary database supports duplicate records then
<tt class="methodname">SecondaryDatabase.get()</tt>
only return the first record found in a matching duplicates set. If you
want to see all the records related to a specific secondary key, then use a
<span>
<tt class="classname">SecondaryCursor</tt> (described in <a href="secondaryCursor.html">
<span>Using Secondary Cursors</span>
</a>).
</span>
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