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Opening and Closing Databases
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Opening and Closing Databases
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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 <tt class="classname">SampleDatabase</tt> 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
{
...
<b class="userinput"><tt> private static final String SUPPLIER_STORE = "supplier_store";
private static final String PART_STORE = "part_store";
private static final String SHIPMENT_STORE = "shipment_store";</tt></b>
...
<b class="userinput"><tt> private Database supplierDb;
private Database partDb;
private Database shipmentDb;</tt></b>
...
} </pre>
<p>
For each database there is a database name constant and a
<tt class="classname">Database</tt> object.
</p>
<p>
The following statements open the three databases by
constructing a Database 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);
...
<b class="userinput"><tt> partDb = env.openDatabase(null, PART_STORE, null, dbConfig);
supplierDb = env.openDatabase(null, SUPPLIER_STORE, null, dbConfig);
shipmentDb = env.openDatabase(null, SHIPMENT_STORE, null, dbConfig);</tt></b>
...
} </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 <tt class="methodname">openDatabase()</tt> 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
{
<b class="userinput"><tt> partDb.close();
supplierDb.close();
shipmentDb.close();</tt></b>
javaCatalog.close();
env.close();
} </pre>
<p>
All databases, including the catalog database, must be 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
{
...
<b class="userinput"><tt> public final Database getPartDatabase()
{
return partDb;
}
public final Database getSupplierDatabase()
{
return supplierDb;
}
public final Database getShipmentDatabase()
{
return shipmentDb;
}</tt></b>
...
}</pre>
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