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Opening and Closing Databases
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<th width="60%" align="center">Chapter 2.
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<h2 class="title" style="clear: both"><a id="opendatabases"></a>
Opening and Closing Databases
</h2>
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<p>
This section describes how to open and close the Part, Supplier
and Shipment databases. A <span class="emphasis"><em>database</em></span> is a collection of
records, each of which has a key and a value. The keys and values
are stored in a selected format, which defines the syntax of the
stored data. Two examples of formats are Java serialization format
and tuple format. In a given database, all keys have the same
format and all values have the same format.
</p>
<p>
The <code class="classname">SampleDatabase</code> class is extended to open and close
the three databases. The following additional class members are
needed.
</p>
<a id="cb_sampledatabase3"></a>
<pre class="programlisting">public class SampleDatabase
{
...
<strong class="userinput"><code> private static final String SUPPLIER_STORE = "supplier_store";
private static final String PART_STORE = "part_store";
private static final String SHIPMENT_STORE = "shipment_store";</code></strong>
...
<strong class="userinput"><code> private Database supplierDb;
private Database partDb;
private Database shipmentDb;</code></strong>
...
} </pre>
<p>
For each database there is a database name constant and a
<code class="classname">Database</code> object.
</p>
<p>
The following statements open the three databases by
constructing a <code class="classname">Database</code> object.
</p>
<a id="cb_java_sampledatabase4"></a>
<pre class="programlisting"> public SampleDatabase(String homeDirectory)
throws DatabaseException, FileNotFoundException
{
...
DatabaseConfig dbConfig = new DatabaseConfig();
dbConfig.setTransactional(true);
dbConfig.setAllowCreate(true);
dbConfig.setType(DatabaseType.BTREE);
...
<strong class="userinput"><code> partDb = env.openDatabase(null, PART_STORE, null, dbConfig);
supplierDb = env.openDatabase(null, SUPPLIER_STORE, null,
dbConfig);
shipmentDb = env.openDatabase(null, SHIPMENT_STORE, null,
dbConfig); </code></strong>
...
} </pre>
<p>
The database configuration object that was used previously for
opening the catalog database is reused for opening the three
databases above. The databases are created if they don't already
exist. The parameters of the <code class="methodname">openDatabase()</code> method were
described earlier when the class catalog database was opened.
</p>
<p>
The following statements close the three databases.
</p>
<a id="cb_close2"></a>
<pre class="programlisting"> public void close()
throws DatabaseException
{
<strong class="userinput"><code> partDb.close();
supplierDb.close();
shipmentDb.close();</code></strong>
javaCatalog.close();
env.close();
} </pre>
<p>
It is recommended that all databases, including the catalog database, is closed
before closing the environment.
</p>
<p>
The following getter methods return the databases for use by
other classes in the example program.
</p>
<a id="cb_sampledatabase_getters"></a>
<pre class="programlisting">public class SampleDatabase
{
...
<strong class="userinput"><code> public final Database getPartDatabase()
{
return partDb;
}
public final Database getSupplierDatabase()
{
return supplierDb;
}
public final Database getShipmentDatabase()
{
return shipmentDb;
}</code></strong>
...
}</pre>
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