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<title>Berkeley DB Reference Guide: Creating collections with entity bindings</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Java API Tutorial - Entity</dl></h3></td>
<td align=right><a href="../bdb_entity/bindings.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../bdb_entity/read.html"><img src="../../images/next.gif" alt="Next"></a>
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<p>
<h3 align=center>Creating collections with entity bindings</h3>
<p>Stored map objects are created in this example in the same way as in
prior examples, but using entity bindings in place of value bindings.  All
value objects passed and returned to the Java collections API are then actually
entity objects (<b>Part</b>, <b>Supplier</b> and <b>Shipment</b>).
The application no longer deals directly with plain value objects
(<b>PartValue</b>, <b>SupplierValue</b> and <b>ShipmentValue</b>).</p>
<hr size=1 noshade>
<p>Since the <b>partValueBinding</b>, <b>supplierValueBinding</b> and
<b>shipmentValueBinding</b> were defined as entity bindings in the prior
section, there are no source code changes necessary for creating the stored map
objects.</p>
<blockquote><pre>
public class SampleViews
{
    ...
    public SampleViews(SampleDatabase db)
    {
        ...
        partMap =
            new StoredMap(db.getPartStore(),
                          partKeyBinding, partValueBinding, true);
        supplierMap =
            new StoredMap(db.getSupplierStore(),
                          supplierKeyBinding, supplierValueBinding, true);
        shipmentMap =
            new StoredMap(db.getShipmentStore(),
                          shipmentKeyBinding, shipmentValueBinding, true);
    }
</pre></blockquote>
<p>Specifying an 
<a href="../../java/com/sleepycat/bdb/bind/EntityBinding.html">EntityBinding</a>
will select a different 
<a href="../../java/com/sleepycat/bdb/collection/StoredMap.html">StoredMap</a>
constructor, but the syntax is the same.  In general, an entity binding may be
used anywhere that a value binding is used.</p>
<hr size=1 noshade>
<p>The following getter methods are defined for use by other classes in the
example program.  Instead of returning the map's entry set
(
<a href="http://java.sun.com/j2se/1.3/docs/api/java/util/Map.html#entrySet">Map.entrySet</a>
), the map's value set
(
<a href="http://java.sun.com/j2se/1.3/docs/api/java/util/Map.html#values">Map.values</a>
) is returned.  The entry set was
convenient in prior examples because it allowed enumerating all key/value pairs
in the collection.  Since an entity contains the key and the value, enumerating
the value set can now be used more conveniently for the same purpose.</p>
<blockquote><pre>
public class SampleViews
{
    ...
<b>    public StoredValueSet getPartSet()
    {
        return (StoredValueSet) partMap.values();
    }
<p>
    public StoredValueSet getSupplierSet()
    {
        return (StoredValueSet) supplierMap.values();
    }
<p>
    public StoredValueSet getShipmentSet()
    {
        return (StoredValueSet) shipmentMap.values();
    }
</b>    ...
}
</pre></blockquote>
<p>Notice that the collection returned by the
<a href="../../java/com/sleepycat/bdb/collection/StoredMap.html#values">StoredMap.values</a>
 method is
actually a 
<a href="../../java/com/sleepycat/bdb/collection/StoredValueSet.html">StoredValueSet</a>
 and not
just a 
<a href="http://java.sun.com/j2se/1.3/docs/api/java/util/Collection.html">Collection</a>
 as defined by the
<a href="http://java.sun.com/j2se/1.3/docs/api/java/util/Map.html#values">Map.values</a>
 interface.  As long as duplicate keys
are not allowed, this collection will behave as a true set and will disallow
the addition of duplicates, etc.</p>
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