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Creating Collections with Entity Bindings
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<h2 class="title" style="clear: both"><a id="collectionswithentities"></a>
Creating Collections with Entity Bindings
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<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 (<tt class="classname">Part</tt>,
<tt class="classname">Supplier</tt> and <tt class="classname">Shipment</tt>). The application no longer
deals directly with plain value objects (<tt class="classname">PartData</tt>,
<tt class="classname">SupplierData</tt> and <tt class="classname">ShipmentData</tt>).
</p>
<p>
Since the <tt class="literal">partValueBinding</tt>, <tt class="literal">supplierValueBinding</tt>
and <tt class="literal">shipmentValueBinding</tt> were defined as entity bindings in
the prior section, there are no source code changes necessary for
creating the stored map objects.
</p>
<a id="entity_sampleviews2"></a>
<pre class="programlisting">public class SampleViews
{
...
public SampleViews(SampleDatabase db)
{
...
partMap =
new StoredMap(db.getPartDatabase(),
partKeyBinding, partValueBinding, true);
supplierMap =
new StoredMap(db.getSupplierDatabase(),
supplierKeyBinding, supplierValueBinding, true);
shipmentMap =
new StoredMap(db.getShipmentDatabase(),
shipmentKeyBinding, shipmentValueBinding, true);
...
} </pre>
<p>
Specifying an
<a href="../../java/com/sleepycat/bind/EntityBinding.html" target="_top">EntityBinding</a>
will select a different
<a href="../../java/com/sleepycat/collections/StoredMap.html" target="_top">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>
<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/1.5.0/docs/api/java/util/Map.html#entrySet" target="_top">Map.entrySet</a>),
the map's value set
(<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Map.html#values" target="_top">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>
<a id="entity_sampleviews3"></a>
<pre class="programlisting"><b class="userinput"><tt>import com.sleepycat.collections.StoredValueSet;</tt></b>
...
public class SampleViews
{
...
<b class="userinput"><tt> public StoredValueSet getPartSet()
{
return (StoredValueSet) partMap.values();
}
public StoredValueSet getSupplierSet()
{
return (StoredValueSet) supplierMap.values();
}
public StoredValueSet getShipmentSet()
{
return (StoredValueSet) shipmentMap.values();
}</tt></b>
...
} </pre>
<p>
Notice that the collection returned by the
<a href="../../java/com/sleepycat/collections/StoredMap.html#values()" target="_top">StoredMap.values</a>
method is actually a
<a href="../../java/com/sleepycat/collections/StoredValueSet.html" target="_top">StoredValueSet</a>
and not just a
<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html" target="_top">Collection</a>
as defined by the
<a href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/Map.html#values" target="_top">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.
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