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Read with $expand</h1> +<hr /> +<h3 id="how-to-guide-extend-basic-read-scenario-with-support-for-expand">How To Guide - Extend basic read scenario with support for $expand</h3> +<p>This How To Guide shows how to extend the basic read scenario with support for the $expand system query option. +It shows how to call the <code>EntityProvider.writeEntry(...)</code> and <code>EntityProvider.writeEntrySet(...)</code> methods with the necessary <code>EntityProviderWriteProperties</code> set and how to implement the necessary <code>OnWriteEntryContent OnWriteFeedContent</code> callbacks.</p> +<h3 id="prerequisites">Prerequisites</h3> +<p>Setup of <a href="basicread">Basic Read Scenario</a></p> +<h3 id="shortcut">Shortcut</h3> +<p>If you like to directly experiment with the results of the extented basic read scenario, you can use this shortcut: </p> +<ul> +<li>Download and unzip <a href="apache-olingo-tutorial-adv_read_expand.zip">Olingo Tutorial 'Basic Read with $expand extension' Project</a> to your local drive which is your OData Tutorial project folder (referenced as <code>$ODATA_PROJECT_HOME</code> in the tutorial).</li> +<li>Start the command line tool and execute the following command in the folder <code>$ODATA_PROJECT_HOME</code> <ul> +<li><code>mvn eclipse:eclipse clean install</code> </li> +</ul> +</li> +<li>Go into Eclipse and import the project into your workspace by... <ul> +<li>Menu <em>File -> Import</em>... </li> +<li><em>Existing projects into workspace</em>, then choose the <code>$ODATA_PROJECT_HOME</code> folder </li> +<li>Select both projects <em>olingo.odata2.sample.service</em> and <em>olingo.odata2.sample.web</em> and press <em>Finish</em>. </li> +</ul> +</li> +</ul> +<h3 id="set-up-your-development-project">Set Up your development project</h3> +<p>If <a href="basicread">Basic Read Scenario</a> is already set up there is nothing additional to do. Otherwise please refer to the Prerequisites section of the <a href="basicread">Basic Read Scenario</a>.</p> +<h3 id="extend-basic-read-scenario">Extend Basic Read Scenario</h3> +<p>The steps to extend the basic read with $expand support for the Car and Manufacturer entities (not entity sets) are to provide the expanded data via ODataCallbacks and register these for the corresponding navigation properties. </p> +<h3 id="implement-onwriteentrycontent-and-onwritefeedcontent-callbacks">Implement OnWriteEntryContent and OnWriteFeedContent callbacks</h3> +<p>To support <code>$expand</code> for a single entry the interface <code>org.apache.olingo.odata2.api.ep.callback.OnWriteEntryContent</code> must be implemented. This provides the method <code>WriteEntryCallbackResult retrieveEntryResult(WriteEntryCallbackContext context) throws ODataApplicationException;</code> which is called during processing from the <code>EntityProvider</code> to receive the necessary data which than is inlined in the response.</p> +<p>In our sample we create a class <code>MyCallback</code> which implements <code>org.apache.olingo.odata2.api.ep.callback.OnWriteEntryContent</code> in following way:</p> +<h5 id="sample-code">Sample Code</h5> +<div class="codehilite"><pre><span class="nd">@Override</span> +<span class="kd">public</span> <span class="n">WriteEntryCallbackResult</span> <span class="nf">retrieveEntryResult</span><span class="o">(</span><span class="n">WriteEntryCallbackContext</span> <span class="n">context</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ODataApplicationException</span> <span class="o">{</span> +<span class="n">WriteEntryCallbackResult</span> <span class="n">result</span> <span class="o">=</span> <span class="k">new</span> <span class="n">WriteEntryCallbackResult</span><span class="o">();</span> + + <span class="k">try</span> <span class="o">{</span> + <span class="k">if</span> <span class="o">(</span><span class="n">isNavigationFromTo</span><span class="o">(</span><span class="n">context</span><span class="o">,</span> <span class="n">ENTITY_SET_NAME_CARS</span><span class="o">,</span> <span class="n">ENTITY_NAME_MANUFACTURER</span><span class="o">))</span> <span class="o">{</span> + <span class="n">EntityProviderWriteProperties</span> <span class="n">inlineProperties</span> <span class="o">=</span> <span class="n">EntityProviderWriteProperties</span><span class="o">.</span><span class="na">serviceRoot</span><span class="o">(</span><span class="n">serviceRoot</span><span class="o">)</span> + <span class="o">.</span><span class="na">expandSelectTree</span><span class="o">(</span><span class="n">context</span><span class="o">.</span><span class="na">getCurrentExpandSelectTreeNode</span><span class="o">())</span> + <span class="o">.</span><span class="na">build</span><span class="o">();</span> + + <span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">Object</span><span class="o">></span> <span class="n">keys</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="na">extractKeyFromEntryData</span><span class="o">();</span> + <span class="n">Integer</span> <span class="n">carId</span> <span class="o">=</span> <span class="o">(</span><span class="n">Integer</span><span class="o">)</span> <span class="n">keys</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="s">"Id"</span><span class="o">);</span> + <span class="n">result</span><span class="o">.</span><span class="na">setEntryData</span><span class="o">(</span><span class="n">dataStore</span><span class="o">.</span><span class="na">getManufacturerFor</span><span class="o">(</span><span class="n">carId</span><span class="o">));</span> + <span class="n">result</span><span class="o">.</span><span class="na">setInlineProperties</span><span class="o">(</span><span class="n">inlineProperties</span><span class="o">);</span> + <span class="o">}</span> + <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">EdmException</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span> + <span class="c1">// TODO: should be handled and not only logged</span> + <span class="n">LOG</span><span class="o">.</span><span class="na">error</span><span class="o">(</span><span class="s">"Error in $expand handling."</span><span class="o">,</span> <span class="n">e</span><span class="o">);</span> + <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">EntityProviderException</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span> + <span class="c1">// TODO: should be handled and not only logged</span> + <span class="n">LOG</span><span class="o">.</span><span class="na">error</span><span class="o">(</span><span class="s">"Error in $expand handling."</span><span class="o">,</span> <span class="n">e</span><span class="o">);</span> + <span class="o">}</span> + + <span class="k">return</span> <span class="n">result</span><span class="o">;</span> +<span class="o">}</span> +</pre></div> + + +<p>Within this method we first check if the source entity and navigation property are correct for our case (via the method <code>isNavigationFromTo(...):boolean)</code>, then we create the <code>EntityProviderWriteProperties</code> with the new (current) <code>ExpandSelectTreeNode</code>, receive the data from our <code>DataStore</code> and put all into the result which then will be further processed by the <code>EntityProvider</code>.</p> +<h3 id="implementation-for-expand-for-an-entity-set">Implementation for $expand for an entity set</h3> +<p>To support <code>$expand</code> for a feed of entries (entity set) the interface <code>org.apache.olingo.odata2.api.ep.callback.OnWriteFeedContent</code> must be implemented. These provides the method <code>WriteFeedCallbackResult retrieveFeedResult(WriteFeedCallbackContext context) throws ODataApplicationException;</code> which is called during processing from the <code>EntityProvider</code> to receive the necessary data which than is inlined in the response.</p> +<p>It is possible to create an additional callback class but for convenience we expand our already created callback (<code>MyCallback</code>) to implement <code>org.apache.olingo.odata2.api.ep.callback.OnWriteFeedContent</code> and provide the method implementation in following way:</p> +<h5 id="sample-code_1">Sample Code</h5> +<div class="codehilite"><pre><span class="nd">@Override</span> +<span class="kd">public</span> <span class="n">WriteFeedCallbackResult</span> <span class="nf">retrieveFeedResult</span><span class="o">(</span><span class="n">WriteFeedCallbackContext</span> <span class="n">context</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ODataApplicationException</span> <span class="o">{</span> +<span class="n">WriteFeedCallbackResult</span> <span class="n">result</span> <span class="o">=</span> <span class="k">new</span> <span class="n">WriteFeedCallbackResult</span><span class="o">();</span> + <span class="k">try</span> <span class="o">{</span> + <span class="k">if</span><span class="o">(</span><span class="n">isNavigationFromTo</span><span class="o">(</span><span class="n">context</span><span class="o">,</span> <span class="n">ENTITY_SET_NAME_MANUFACTURERS</span><span class="o">,</span> <span class="n">ENTITY_SET_NAME_CARS</span><span class="o">))</span> <span class="o">{</span> + <span class="n">EntityProviderWriteProperties</span> <span class="n">inlineProperties</span> <span class="o">=</span> <span class="n">EntityProviderWriteProperties</span><span class="o">.</span><span class="na">serviceRoot</span><span class="o">(</span><span class="n">serviceRoot</span><span class="o">)</span> + <span class="o">.</span><span class="na">expandSelectTree</span><span class="o">(</span><span class="n">context</span><span class="o">.</span><span class="na">getCurrentExpandSelectTreeNode</span><span class="o">())</span> + <span class="o">.</span><span class="na">selfLink</span><span class="o">(</span><span class="n">context</span><span class="o">.</span><span class="na">getSelfLink</span><span class="o">())</span> + <span class="o">.</span><span class="na">build</span><span class="o">();</span> + + <span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">Object</span><span class="o">></span> <span class="n">keys</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="na">extractKeyFromEntryData</span><span class="o">();</span> + <span class="n">Integer</span> <span class="n">manufacturerId</span> <span class="o">=</span> <span class="o">(</span><span class="n">Integer</span><span class="o">)</span> <span class="n">keys</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="s">"Id"</span><span class="o">);</span> + <span class="n">result</span><span class="o">.</span><span class="na">setFeedData</span><span class="o">(</span><span class="n">dataStore</span><span class="o">.</span><span class="na">getCarsFor</span><span class="o">(</span><span class="n">manufacturerId</span><span class="o">));</span> + <span class="n">result</span><span class="o">.</span><span class="na">setInlineProperties</span><span class="o">(</span><span class="n">inlineProperties</span><span class="o">);</span> + <span class="o">}</span> + <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">EdmException</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span> + <span class="c1">// TODO: should be handled and not only logged</span> + <span class="n">LOG</span><span class="o">.</span><span class="na">error</span><span class="o">(</span><span class="s">"Error in $expand handling."</span><span class="o">,</span> <span class="n">e</span><span class="o">);</span> + <span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">EntityProviderException</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span> + <span class="c1">// TODO: should be handled and not only logged</span> + <span class="n">LOG</span><span class="o">.</span><span class="na">error</span><span class="o">(</span><span class="s">"Error in $expand handling."</span><span class="o">,</span> <span class="n">e</span><span class="o">);</span> + <span class="o">}</span> + <span class="k">return</span> <span class="n">result</span><span class="o">;</span> +<span class="o">}</span> +</pre></div> + + +<p>Within this method we first check if the source entity and navigation property are correct for our case (via the method <code>isNavigationFromTo(...):boolean)</code>, then we create the <code>EntityProviderWriteProperties</code> with the new (current) <code>ExpandSelectTreeNode</code>, receive the data from our <code>DataStore</code> and put all into the result which then will be further processed by the <code>EntityProvider</code>.</p> +<p>This example shows that the basic callback logic between <code>OnWriteEntryConten</code>t and <code>OnWriteFeedContent</code> is very similar. Validation of current element (optional), preparing of <code>EntityProviderWriteProperties</code>, receive of data and putting all together into corresponding result object (<code>WriteEntryCallbackResult</code> or <code>WriteFeedCallbackResult</code>).</p> +<p>To improve code readability the <code>isNavigationFromTo(...):boolean</code> method was also added to the class. The method is used to check if the retrieved request is related to given entity set and navigation:</p> +<h4 id="sample-code_2">Sample Code</h4> +<div class="codehilite"><pre><span class="kd">private</span> <span class="kt">boolean</span> <span class="nf">isNavigationFromTo</span><span class="o">(</span><span class="n">WriteCallbackContext</span> <span class="n">context</span><span class="o">,</span> <span class="n">String</span> <span class="n">entitySetName</span><span class="o">,</span> <span class="n">String</span> <span class="n">navigationPropertyName</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">EdmException</span> <span class="o">{</span> + <span class="k">if</span><span class="o">(</span><span class="n">entitySetName</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">||</span> <span class="n">navigationPropertyName</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span> + <span class="k">return</span> <span class="kc">false</span><span class="o">;</span> + <span class="o">}</span> + <span class="n">EdmEntitySet</span> <span class="n">sourceEntitySet</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="na">getSourceEntitySet</span><span class="o">();</span> + <span class="n">EdmNavigationProperty</span> <span class="n">navigationProperty</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="na">getNavigationProperty</span><span class="o">();</span> + <span class="k">return</span> <span class="n">entitySetName</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">sourceEntitySet</span><span class="o">.</span><span class="na">getName</span><span class="o">())</span> <span class="o">&&</span> <span class="n">navigationPropertyName</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">navigationProperty</span><span class="o">.</span><span class="na">getName</span><span class="o">());</span> +<span class="o">}</span> +</pre></div> + + +<h3 id="extend-odatasingleprocessorreadentity">Extend ODataSingleProcessor.readEntity(...)</h3> +<p>The necessary callbacks (<code>MyCallback</code> class) now has to be registered during the corresponding <code>readEntity(...)</code> call. Therefore we first create a map with the property name as key and the according callback as value. Additional we need to create the <code>ExpandSelectTreeNode</code> based on current element position. Both then have to be set in the <code>EntityProviderWritePropertiesBuilder</code>. </p> +<p>The following code show the few lines we need for extending the read of a car with its expanded manufacturer.</p> +<div class="codehilite"><pre><span class="c1">// create and register callback</span> +<span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">></span> <span class="n">callbacks</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashMap</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">>();</span> +<span class="n">callbacks</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">ENTITY_NAME_MANUFACTURER</span><span class="o">,</span> <span class="k">new</span> <span class="n">MyCallback</span><span class="o">(</span><span class="n">dataStore</span><span class="o">,</span> <span class="n">serviceRoot</span><span class="o">));</span> +<span class="n">ExpandSelectTreeNode</span> <span class="n">expandSelectTreeNode</span> <span class="o">=</span> <span class="n">UriParser</span><span class="o">.</span><span class="na">createExpandSelectTree</span><span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getSelect</span><span class="o">(),</span> <span class="n">uriInfo</span><span class="o">.</span><span class="na">getExpand</span><span class="o">());</span> +<span class="n">propertiesBuilder</span><span class="o">.</span><span class="na">expandSelectTree</span><span class="o">(</span><span class="n">expandSelectTreeNode</span><span class="o">).</span><span class="na">callbacks</span><span class="o">(</span><span class="n">callbacks</span><span class="o">);</span> +</pre></div> + + +<p>The following code show the few lines we need for extending the read of a manufacturer with its expanded cars.</p> +<div class="codehilite"><pre><span class="c1">// create and register callback</span> +<span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">></span> <span class="n">callbacks</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashMap</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">>();</span> +<span class="n">callbacks</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">ENTITY_SET_NAME_CARS</span><span class="o">,</span> <span class="k">new</span> <span class="n">MyCallback</span><span class="o">(</span><span class="n">dataStore</span><span class="o">,</span> <span class="n">serviceRoot</span><span class="o">));</span> +<span class="n">ExpandSelectTreeNode</span> <span class="n">expandSelectTreeNode</span> <span class="o">=</span> <span class="n">UriParser</span><span class="o">.</span><span class="na">createExpandSelectTree</span><span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getSelect</span><span class="o">(),</span> <span class="n">uriInfo</span><span class="o">.</span><span class="na">getExpand</span><span class="o">());</span> +<span class="n">propertiesBuilder</span><span class="o">.</span><span class="na">expandSelectTree</span><span class="o">(</span><span class="n">expandSelectTreeNode</span><span class="o">).</span><span class="na">callbacks</span><span class="o">(</span><span class="n">callbacks</span><span class="o">);</span> +</pre></div> + + +<p>The complete <code>readEntity(...)</code> method should now look like:</p> +<div class="codehilite"><pre><span class="kd">public</span> <span class="n">ODataResponse</span> <span class="nf">readEntity</span><span class="o">(</span><span class="n">GetEntityUriInfo</span> <span class="n">uriInfo</span><span class="o">,</span> <span class="n">String</span> <span class="n">contentType</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ODataException</span> <span class="o">{</span> + + <span class="k">if</span> <span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getNavigationSegments</span><span class="o">().</span><span class="na">size</span><span class="o">()</span> <span class="o">==</span> <span class="mi">0</span><span class="o">)</span> <span class="o">{</span> + <span class="n">EdmEntitySet</span> <span class="n">entitySet</span> <span class="o">=</span> <span class="n">uriInfo</span><span class="o">.</span><span class="na">getStartEntitySet</span><span class="o">();</span> + + <span class="k">if</span> <span class="o">(</span><span class="n">ENTITY_SET_NAME_CARS</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">entitySet</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span> + <span class="kt">int</span> <span class="n">id</span> <span class="o">=</span> <span class="n">getKeyValue</span><span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getKeyPredicates</span><span class="o">().</span><span class="na">get</span><span class="o">(</span><span class="mi">0</span><span class="o">));</span> + <span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">Object</span><span class="o">></span> <span class="n">data</span> <span class="o">=</span> <span class="n">dataStore</span><span class="o">.</span><span class="na">getCar</span><span class="o">(</span><span class="n">id</span><span class="o">);</span> + + <span class="k">if</span> <span class="o">(</span><span class="n">data</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span> + <span class="n">URI</span> <span class="n">serviceRoot</span> <span class="o">=</span> <span class="n">getContext</span><span class="o">().</span><span class="na">getPathInfo</span><span class="o">().</span><span class="na">getServiceRoot</span><span class="o">();</span> + <span class="n">ODataEntityProviderPropertiesBuilder</span> <span class="n">propertiesBuilder</span> <span class="o">=</span> <span class="n">EntityProviderWriteProperties</span><span class="o">.</span><span class="na">serviceRoot</span><span class="o">(</span><span class="n">serviceRoot</span><span class="o">);</span> + + <span class="c1">// create and register callback</span> + <span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">></span> <span class="n">callbacks</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashMap</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">>();</span> + <span class="n">callbacks</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">ENTITY_NAME_MANUFACTURER</span><span class="o">,</span> <span class="k">new</span> <span class="n">MyCallback</span><span class="o">(</span><span class="n">dataStore</span><span class="o">,</span> <span class="n">serviceRoot</span><span class="o">));</span> + <span class="n">ExpandSelectTreeNode</span> <span class="n">expandSelectTreeNode</span> <span class="o">=</span> <span class="n">UriParser</span><span class="o">.</span><span class="na">createExpandSelectTree</span><span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getSelect</span><span class="o">(),</span> <span class="n">uriInfo</span><span class="o">.</span><span class="na">getExpand</span><span class="o">());</span> + <span class="c1">//</span> + <span class="n">propertiesBuilder</span><span class="o">.</span><span class="na">expandSelectTree</span><span class="o">(</span><span class="n">expandSelectTreeNode</span><span class="o">).</span><span class="na">callbacks</span><span class="o">(</span><span class="n">callbacks</span><span class="o">);</span> + + <span class="k">return</span> <span class="n">EntityProvider</span><span class="o">.</span><span class="na">writeEntry</span><span class="o">(</span><span class="n">contentType</span><span class="o">,</span> <span class="n">entitySet</span><span class="o">,</span> <span class="n">data</span><span class="o">,</span> <span class="n">propertiesBuilder</span><span class="o">.</span><span class="na">build</span><span class="o">());</span> + <span class="o">}</span> + <span class="o">}</span> <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="n">ENTITY_SET_NAME_MANUFACTURERS</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">entitySet</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span> + <span class="kt">int</span> <span class="n">id</span> <span class="o">=</span> <span class="n">getKeyValue</span><span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getKeyPredicates</span><span class="o">().</span><span class="na">get</span><span class="o">(</span><span class="mi">0</span><span class="o">));</span> + <span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">Object</span><span class="o">></span> <span class="n">data</span> <span class="o">=</span> <span class="n">dataStore</span><span class="o">.</span><span class="na">getManufacturer</span><span class="o">(</span><span class="n">id</span><span class="o">);</span> + + <span class="k">if</span> <span class="o">(</span><span class="n">data</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span> + <span class="n">URI</span> <span class="n">serviceRoot</span> <span class="o">=</span> <span class="n">getContext</span><span class="o">().</span><span class="na">getPathInfo</span><span class="o">().</span><span class="na">getServiceRoot</span><span class="o">();</span> + <span class="n">ODataEntityProviderPropertiesBuilder</span> <span class="n">propertiesBuilder</span> <span class="o">=</span> <span class="n">EntityProviderWriteProperties</span><span class="o">.</span><span class="na">serviceRoot</span><span class="o">(</span><span class="n">serviceRoot</span><span class="o">);</span> + + <span class="c1">// create and register callback</span> + <span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">></span> <span class="n">callbacks</span> <span class="o">=</span> <span class="k">new</span> <span class="n">HashMap</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">ODataCallback</span><span class="o">>();</span> + <span class="n">callbacks</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">ENTITY_SET_NAME_CARS</span><span class="o">,</span> <span class="k">new</span> <span class="n">MyCallback</span><span class="o">(</span><span class="n">dataStore</span><span class="o">,</span> <span class="n">serviceRoot</span><span class="o">));</span> + <span class="n">ExpandSelectTreeNode</span> <span class="n">expandSelectTreeNode</span> <span class="o">=</span> <span class="n">UriParser</span><span class="o">.</span><span class="na">createExpandSelectTree</span><span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getSelect</span><span class="o">(),</span> <span class="n">uriInfo</span><span class="o">.</span><span class="na">getExpand</span><span class="o">());</span> + <span class="c1">//</span> + <span class="n">propertiesBuilder</span><span class="o">.</span><span class="na">expandSelectTree</span><span class="o">(</span><span class="n">expandSelectTreeNode</span><span class="o">).</span><span class="na">callbacks</span><span class="o">(</span><span class="n">callbacks</span><span class="o">);</span> + + <span class="k">return</span> <span class="n">EntityProvider</span><span class="o">.</span><span class="na">writeEntry</span><span class="o">(</span><span class="n">contentType</span><span class="o">,</span> <span class="n">entitySet</span><span class="o">,</span> <span class="n">data</span><span class="o">,</span> <span class="n">propertiesBuilder</span><span class="o">.</span><span class="na">build</span><span class="o">());</span> + <span class="o">}</span> + <span class="o">}</span> + + <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataNotFoundException</span><span class="o">(</span><span class="n">ODataNotFoundException</span><span class="o">.</span><span class="na">ENTITY</span><span class="o">);</span> + + <span class="o">}</span> <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getNavigationSegments</span><span class="o">().</span><span class="na">size</span><span class="o">()</span> <span class="o">==</span> <span class="mi">1</span><span class="o">)</span> <span class="o">{</span> + <span class="c1">//navigation first level, simplified example for illustration purposes only</span> + <span class="n">EdmEntitySet</span> <span class="n">entitySet</span> <span class="o">=</span> <span class="n">uriInfo</span><span class="o">.</span><span class="na">getTargetEntitySet</span><span class="o">();</span> + <span class="k">if</span> <span class="o">(</span><span class="n">ENTITY_SET_NAME_MANUFACTURERS</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">entitySet</span><span class="o">.</span><span class="na">getName</span><span class="o">()))</span> <span class="o">{</span> + <span class="kt">int</span> <span class="n">carKey</span> <span class="o">=</span> <span class="n">getKeyValue</span><span class="o">(</span><span class="n">uriInfo</span><span class="o">.</span><span class="na">getKeyPredicates</span><span class="o">().</span><span class="na">get</span><span class="o">(</span><span class="mi">0</span><span class="o">));</span> + <span class="k">return</span> <span class="n">EntityProvider</span><span class="o">.</span><span class="na">writeEntry</span><span class="o">(</span><span class="n">contentType</span><span class="o">,</span> <span class="n">uriInfo</span><span class="o">.</span><span class="na">getTargetEntitySet</span><span class="o">(),</span> <span class="n">dataStore</span><span class="o">.</span><span class="na">getManufacturer</span><span class="o">(</span><span class="n">carKey</span><span class="o">),</span> <span class="n">EntityProviderWriteProperties</span><span class="o">.</span><span class="na">serviceRoot</span><span class="o">(</span><span class="n">getContext</span><span class="o">().</span><span class="na">getPathInfo</span><span class="o">().</span><span class="na">getServiceRoot</span><span class="o">()).</span><span class="na">build</span><span class="o">());</span> + <span class="o">}</span> + + <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataNotFoundException</span><span class="o">(</span><span class="n">ODataNotFoundException</span><span class="o">.</span><span class="na">ENTITY</span><span class="o">);</span> + <span class="o">}</span> + + <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataNotImplementedException</span><span class="o">();</span> +<span class="o">}</span> +</pre></div> + + +<p>Now we can test out <code>$expand</code> extension in the web application.</p> +<h3 id="deploy-run-and-test-expand">Deploy, run and test $expand</h3> +<p>Like in the basic read scenario follow these steps:</p> +<ul> +<li>Build your project: <code>mvn clean install</code> </li> +<li>When build finished in Eclipse, run the Web Application via <em>Run As -> Run on Server</em> </li> +<li>After successful server start and deployment the following uris from the basic read sample work as before: <ul> +<li>Show the Manufacturers: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers";>http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers</a> </li> +<li>Show one Manufacturer: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers(1)">http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers(1)</a> </li> +<li>Show the Cars: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars";>http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars</a> </li> +<li>Show one Car: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars(2)">http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars(2)</a> </li> +<li>Show the related Manufacturer of a Car: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars(2)/Manufacturer">http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars(2)/Manufacturer</a> </li> +<li>Show the related Cars of a Manufacturer: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers(1)/Cars">http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers(1)/Cars</a> </li> +</ul> +</li> +<li>And in addition we can now expand the car and manufacturer with each other: <ul> +<li>Show Car with its Manufacturer: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars(2)?$expand=Manufacturer">http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Cars(2)?$expand=Manufacturer </a></li> +<li>Show Manufacturer with its Cars: <a href="http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers(1)?$expand=Cars">http://localhost:8080/olingo.odata2.sample.cars.web/MyODataSample.svc/Manufacturers(1)?$expand=Cars</a> </li> +</ul> +</li> +</ul> +<h3 id="further-information">Further Information</h3> +<p>Next extension step for read scenario are read of <a href="read_media-resource">Media Resources</a>. 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