mirror of
https://github.com/berkeleydb/je.git
synced 2024-09-09 03:56:13 +00:00
241 lines
8.7 KiB
HTML
241 lines
8.7 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
||
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
<html xmlns="http://www.w3.org/1999/xhtml">
|
||
<head>
|
||
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
||
<title>Implementing Key Creators</title>
|
||
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
||
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
||
<link rel="start" href="index.html" title="Getting Started with Berkeley DB Java Edition" />
|
||
<link rel="up" href="indexes.html" title="Chapter 10. Secondary Databases" />
|
||
<link rel="prev" href="indexes.html" title="Chapter 10. Secondary Databases" />
|
||
<link rel="next" href="secondaryProps.html" title="Secondary Database Properties" />
|
||
</head>
|
||
<body>
|
||
<div xmlns="" class="navheader">
|
||
<div class="libver">
|
||
<p>Library Version 12.2.7.5</p>
|
||
</div>
|
||
<table width="100%" summary="Navigation header">
|
||
<tr>
|
||
<th colspan="3" align="center">Implementing Key
|
||
<span xmlns="http://www.w3.org/1999/xhtml">Creators</span>
|
||
|
||
</th>
|
||
</tr>
|
||
<tr>
|
||
<td width="20%" align="left"><a accesskey="p" href="indexes.html">Prev</a> </td>
|
||
<th width="60%" align="center">Chapter 10. Secondary Databases</th>
|
||
<td width="20%" align="right"> <a accesskey="n" href="secondaryProps.html">Next</a></td>
|
||
</tr>
|
||
</table>
|
||
<hr />
|
||
</div>
|
||
<div class="sect1" lang="en" xml:lang="en">
|
||
<div class="titlepage">
|
||
<div>
|
||
<div>
|
||
<h2 class="title" style="clear: both"><a id="keyCreator"></a>Implementing Key
|
||
<span>Creators</span>
|
||
|
||
</h2>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<p>
|
||
You must provide every secondary database with a
|
||
<span>class</span>
|
||
|
||
that creates keys from primary records. You identify this
|
||
<span>class</span>
|
||
|
||
|
||
<span>
|
||
using the <code class="methodname">SecondaryConfig.setKeyCreator()</code>
|
||
method.
|
||
</span>
|
||
|
||
</p>
|
||
<p>
|
||
You can create keys using whatever data you want. Typically you will
|
||
base your key on some information found in a record's data, but you
|
||
can also use information found in the primary record's key. How you build
|
||
your keys is entirely dependent upon the nature of the index that you
|
||
want to maintain.
|
||
</p>
|
||
<p>
|
||
You implement a key creator by writing a class that implements the
|
||
<code class="classname">SecondaryKeyCreator</code> interface. This interface
|
||
requires you to implement the <code class="methodname">SecondaryKeyCreator.createSecondaryKey()</code>
|
||
method.
|
||
</p>
|
||
<p>
|
||
One thing to remember when implementing this method is that you will
|
||
need a way to extract the necessary information from the data's
|
||
<code class="classname">DatabaseEntry</code> and/or the key's
|
||
<code class="classname">DatabaseEntry</code> that are provided on calls to this
|
||
method. If you are using complex objects, then you are probably using the
|
||
Bind APIs to perform this conversion. The easiest thing to do is to
|
||
instantiate the <code class="classname">EntryBinding</code> or
|
||
<code class="classname">TupleBinding</code> that you need to perform the
|
||
conversion, and then provide this to your key creator's constructor.
|
||
The Bind APIs are introduced in <a class="xref" href="bindAPI.html" title="Using the BIND APIs">Using the BIND APIs</a>.
|
||
</p>
|
||
<p>
|
||
<code class="methodname">SecondaryKeyCreator.createSecondaryKey()</code> returns a
|
||
boolean. A return value of <code class="literal">false</code> indicates that
|
||
no secondary key exists, and therefore no record should be added to the secondary database for that primary record.
|
||
If a record already exists in the secondary database, it is deleted.
|
||
</p>
|
||
<p>
|
||
For example, suppose your primary database uses the following class
|
||
for its record data:
|
||
</p>
|
||
<a id="je_index3"></a>
|
||
<pre class="programlisting">package je.gettingStarted;
|
||
|
||
public class PersonData {
|
||
private String userID;
|
||
private String surname;
|
||
private String familiarName;
|
||
|
||
public PersonData(String userID, String surname,
|
||
String familiarName) {
|
||
this.userID = userID;
|
||
this.surname = surname;
|
||
this.familiarName = familiarName;
|
||
}
|
||
|
||
public String getUserID() {
|
||
return userID;
|
||
}
|
||
|
||
public String getSurname() {
|
||
return surname;
|
||
}
|
||
|
||
public String getFamiliarName() {
|
||
return familiarName;
|
||
}
|
||
} </pre>
|
||
<p>
|
||
Also, suppose that you have created a custom tuple binding,
|
||
<code class="classname">PersonDataBinding</code>, that you use to convert
|
||
<code class="classname">PersonData</code> objects to and from
|
||
<code class="classname">DatabaseEntry</code> objects. (Custom tuple bindings are
|
||
described in <a class="xref" href="bindAPI.html#customTuple" title="Custom Tuple Bindings">Custom Tuple Bindings</a>.)
|
||
</p>
|
||
<p>
|
||
Finally, suppose you want a secondary database that is keyed based
|
||
on the person's full name.
|
||
</p>
|
||
<p>
|
||
Then in this case you might create a key creator as follows:
|
||
</p>
|
||
<a id="je_index4"></a>
|
||
<pre class="programlisting">package je.gettingStarted;
|
||
|
||
import com.sleepycat.bind.tuple.TupleBinding;
|
||
|
||
import com.sleepycat.je.SecondaryKeyCreator;
|
||
import com.sleepycat.je.DatabaseEntry;
|
||
import com.sleepycat.je.DatabaseException;
|
||
import com.sleepycat.je.SecondaryDatabase;
|
||
|
||
import java.io.IOException;
|
||
|
||
public class FullNameKeyCreator implements SecondaryKeyCreator {
|
||
|
||
private TupleBinding theBinding;
|
||
|
||
public FullNameKeyCreator(TupleBinding theBinding1) {
|
||
theBinding = theBinding1;
|
||
}
|
||
|
||
public boolean createSecondaryKey(SecondaryDatabase secDb,
|
||
DatabaseEntry keyEntry,
|
||
DatabaseEntry dataEntry,
|
||
DatabaseEntry resultEntry) {
|
||
|
||
try {
|
||
PersonData pd =
|
||
(PersonData) theBinding.entryToObject(dataEntry);
|
||
String fullName = pd.getFamiliarName() + " " +
|
||
pd.getSurname();
|
||
resultEntry.setData(fullName.getBytes("UTF-8"));
|
||
} catch (IOException willNeverOccur) {}
|
||
return true;
|
||
}
|
||
} </pre>
|
||
<p>Finally, you use this key creator as follows:</p>
|
||
<a id="je_index5"></a>
|
||
<pre class="programlisting">package je.gettingStarted;
|
||
|
||
import com.sleepycat.bind.tuple.TupleBinding;
|
||
|
||
import com.sleepycat.je.Database;
|
||
import com.sleepycat.je.DatabaseException;
|
||
import com.sleepycat.je.Environment;
|
||
import com.sleepycat.je.SecondaryDatabase;
|
||
import com.sleepycat.je.SecondaryConfig;
|
||
|
||
...
|
||
|
||
Environment myEnv = null;
|
||
Database myDb = null;
|
||
SecondaryDatabase mySecDb = null;
|
||
try {
|
||
// Environment and primary database open omitted for brevity
|
||
...
|
||
|
||
TupleBinding myDataBinding = new MyTupleBinding();
|
||
FullNameKeyCreator fnkc = new FullNameKeyCreator(myDataBinding);
|
||
|
||
SecondaryConfig mySecConfig = new SecondaryConfig();
|
||
mySecConfig.setKeyCreator(fnkc);
|
||
|
||
//Perform the actual open
|
||
String secDbName = "mySecondaryDatabase";
|
||
mySecDb = myEnv.openSecondaryDatabase(null, secDbName, myDb,
|
||
mySecConfig);
|
||
} catch (DatabaseException de) {
|
||
// Exception handling goes here
|
||
} finally {
|
||
try {
|
||
if (mySecDb != null) {
|
||
mySecDb.close();
|
||
}
|
||
|
||
if (myDb != null) {
|
||
myDb.close();
|
||
}
|
||
|
||
if (myEnv != null) {
|
||
myEnv.close();
|
||
}
|
||
} catch (DatabaseException dbe) {
|
||
// Exception handling goes here
|
||
}
|
||
}</pre>
|
||
</div>
|
||
<div class="navfooter">
|
||
<hr />
|
||
<table width="100%" summary="Navigation footer">
|
||
<tr>
|
||
<td width="40%" align="left"><a accesskey="p" href="indexes.html">Prev</a> </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="u" href="indexes.html">Up</a>
|
||
</td>
|
||
<td width="40%" align="right"> <a accesskey="n" href="secondaryProps.html">Next</a></td>
|
||
</tr>
|
||
<tr>
|
||
<td width="40%" align="left" valign="top">Chapter 10. Secondary Databases </td>
|
||
<td width="20%" align="center">
|
||
<a accesskey="h" href="index.html">Home</a>
|
||
</td>
|
||
<td width="40%" align="right" valign="top"> Secondary Database Properties</td>
|
||
</tr>
|
||
</table>
|
||
</div>
|
||
</body>
|
||
</html>
|