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Posted to commits@olingo.apache.org by bu...@apache.org on 2015/09/01 13:08:42 UTC
svn commit: r963848 - in /websites/staging/olingo/trunk/content: ./
doc/odata4/tutorials/sqo_f/
Author: buildbot
Date: Tue Sep 1 11:08:42 2015
New Revision: 963848
Log:
Staging update by buildbot for olingo
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websites/staging/olingo/trunk/content/doc/odata4/tutorials/sqo_f/
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@@ -0,0 +1,660 @@
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+<h1 id="how-to-build-an-odata-service-with-olingo-v4">How to build an OData Service with Olingo V4<a class="headerlink" href="#how-to-build-an-odata-service-with-olingo-v4" title="Permanent link">¶</a></h1>
+<h1 id="part-54-system-query-options-filter">Part 5.4: System Query Options: $filter<a class="headerlink" href="#part-54-system-query-options-filter" title="Permanent link">¶</a></h1>
+<h2 id="introduction">Introduction<a class="headerlink" href="#introduction" title="Permanent link">¶</a></h2>
+<p>In the present tutorial, weâll continue implementing OData system query options, this time focusing on <strong>$filter</strong></p>
+<p><strong>Note:</strong>
+The full implementation of the OData service as described in the present tutorial can be found in the attached zip file that contains an Eclipse project that can be imported into your Eclipse workspace.</p>
+<p>Table of Contents</p>
+<ol>
+<li>Preparation</li>
+<li>Implementation</li>
+<li>Implement $filter </li>
+<li>Run the implemented service</li>
+<li>Summary</li>
+<li>Links</li>
+</ol>
+<h1 id="1-preparation">1. Preparation<a class="headerlink" href="#1-preparation" title="Permanent link">¶</a></h1>
+<p>Follow <em>Tutorial Part 1: Read Entity Collection</em> and <em>Tutorial Part 2: Read Entity</em> or as shortcut import the project attached to Tutorial Part 2 into your Eclipse workspace.</p>
+<p>Afterwards do a <em>Deploy and run</em>: it should be working.</p>
+<h1 id="2-implementation">2. Implementation<a class="headerlink" href="#2-implementation" title="Permanent link">¶</a></h1>
+<p>The system query options weâre focusing on are applied to the entity collection only, therefore our
+implementation for the $filter query options is done in the class
+<em>myservice.mynamespace.service.DemoEntityCollectionProcessor</em></p>
+<p>The general sequence is again:</p>
+<ol>
+<li>Analyze the URI</li>
+<li>Fetch data from backend</li>
+<li>Apply the system query option</li>
+<li>Serialize</li>
+<li>Configure the response</li>
+</ol>
+<h3 id="21-implement-filter">2.1 Implement $filter<a class="headerlink" href="#21-implement-filter" title="Permanent link">¶</a></h3>
+<h4 id="background">Background<a class="headerlink" href="#background" title="Permanent link">¶</a></h4>
+<p>When requesting a list of entities from a service, the default behavior is to return all entities on the list. The consumer of an OData service might want to be able to receive a sub set by specifying certain criteria which each of the returned entities have to fulfill.<br />
+For example, a usual case would be to request all products with a specified minimum and maximum price.
+OData supports this requirement with the system query option <strong>$filter</strong></p>
+<p>It is specified as follows:</p>
+<div class="codehilite"><pre>$<span class="n">filter</span><span class="p">=</span><span class="o"><</span><span class="n">BooleanExpression</span><span class="o">></span>
+</pre></div>
+
+
+<p>See here for more details: <br />
+<a href="http://docs.oasis-open.org/odata/odata/v4.0/errata02/os/complete/part1-protocol/odata-v4.0-errata02-os-part1-protocol-complete.html#_Toc406398301">OData Version 4.0 Part 1: Protocol Plus Errata 02</a></p>
+<p><a href="http://docs.oasis-open.org/odata/odata/v4.0/errata02/os/complete/part2-url-conventions/odata-v4.0-errata02-os-part2-url-conventions-complete.html#_Toc406398094">OData Version 4.0 Part 2: URL Conventions Plus Errata 02</a></p>
+<p>The expression given by the <strong>$filter</strong> query option have to return a Boolean value when applied to a certain entity on the entity list. Iff the value returned for a given entity is <em>âtrueâ</em>, the service has to return the entity. Otherwise the service has to discard the entity.</p>
+<p><strong>Example</strong></p>
+<p>First, just to remember how the full payload looks like, the ânormalâ query of the product:</p>
+<p><a href="http://localhost:8080/DemoService/DemoService.svc/Products">http://localhost:8080/DemoService/DemoService.svc/Products</a></p>
+<p><img alt="AllProductsWithoutFilter" src="no_filter.png" title="All products without filter" /></p>
+<p>Now have a look to the following Uri:<br />
+<a href="[http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID eq 1 or contains(Description,'1280')">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID eq 1 or contains(Description,'1280')</a></p>
+<p>The $filter system query option has been applied to the Products Entity Collection. The client requests all products which fulfills the following condition: ID equals to one or the Description should contain the string â1280â</p>
+<p><img alt="ProductsWithFilter" src="filter_applied.png" title="Products with applied $filter" /></p>
+<p><strong>Visitor pattern</strong></p>
+<p>First things first, the Uri parser creates an <em>abstract syntax tree</em> (AST). An abstract syntax tree describes the expression in a hierarchical way. For example to calculate the root node, all nodes below have to be calculated first. The idea is to traverse the tree in pre order (depth-first).</p>
+<p>Consider the following Uri </p>
+<div class="codehilite"><pre>â<span class="o">/</span><span class="n">Products</span>?$<span class="n">format</span><span class="p">=(</span><span class="n">Price</span> <span class="n">lt</span> 2000<span class="p">)</span> <span class="n">and</span> <span class="n">contains</span><span class="p">(</span><span class="n">Description</span><span class="p">,</span>â<span class="n">Notebook</span>â<span class="p">)</span>â<span class="p">.</span>
+</pre></div>
+
+
+<p>As you can see, the intention is to request all Products, which costs less than 2000 monetary units and contains the word âNotebookâ in their description. The expression is split up in two parts by the binary operator âandâ. To calculate the result of the âandâ node, the left and also the right child have to be calculated first. The left child itself is another binary operation. So to calculate âless thanâ the type and value of the property âPriceâ has to be determined. And so onâ¦</p>
+<p><img alt="AbstractSyntaxTree" src="ast.png" title="Abstract syntax tree of the filter expression âPrice lt 2000 and contains(Description,âNotebookâ)" /></p>
+<p>Key<br />
+<img alt="AbstractSyntaxTree" src="keyAST.png" title="Key abstract syntax tree" /></p>
+<p>So the following actions have to be done:</p>
+<table class="table">
+<thead>
+<tr>
+<th align="left">Action</th>
+<th>Result - Type</th>
+<th>Result</th>
+<th>Method</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td align="left">1. Get the value of the property âPriceâ</td>
+<td>Edm.Double</td>
+<td>500.00</td>
+<td>visitMember</td>
+</tr>
+<tr>
+<td align="left">2. Determine the Type and value of the literal 2000.00</td>
+<td>Edm.Double</td>
+<td>2000.00</td>
+<td>visitLiteral</td>
+</tr>
+<tr>
+<td align="left">3. Calculate â 500.00 <strong>lt</strong> 2000</td>
+<td>Edm.Boolean</td>
+<td>true</td>
+<td>visitBinaryOperator</td>
+</tr>
+<tr>
+<td align="left">4. Get the value of the Property âDescriptionâ</td>
+<td>Edm.String</td>
+<td>"Notebook basic..."</td>
+<td>visitMember</td>
+</tr>
+<tr>
+<td align="left">5. Determine the type and value of the literal âNotebookâ</td>
+<td>Edm.String</td>
+<td>âNotebookâ</td>
+<td>visitLiteral</td>
+</tr>
+<tr>
+<td align="left">6. Calculate â <strong>contains</strong>(âNotebook Basicâ¦â, âNotebookâ)</td>
+<td>Edm.Boolean</td>
+<td>true</td>
+<td>visitMethodCall</td>
+</tr>
+<tr>
+<td align="left">7. Calculate â true <strong>and</strong> true</td>
+<td>Edm.Boolean</td>
+<td>true</td>
+<td>visitBinaryOperator</td>
+</tr>
+</tbody>
+</table>
+<p>Olingo uses the vistor pattern to traverse the AST. Each of these actions is mapped to one method of the ExpressionVistor. You can see the name of the methods in last column of table 1. As service developer we have to implement this methods but we don`t have to take care about calling them. The libaray will call the proper method and we have only to calculate the result. </p>
+<h4 id="implementation">Implementation<a class="headerlink" href="#implementation" title="Permanent link">¶</a></h4>
+<p>First we will create the <em>Filter Expression Visitor</em> and after that, we`ll integrate the just created Visitor in <em>EntityCollectionProcessor</em>.</p>
+<p><strong>1.1 Create our FilterExpressionVisitor</strong></p>
+<p>Create a new class <em>FilterExpressionVisitor</em> in package <em>myservice.mynamespace.service</em> and<br />
+implement the Interface <em>org.apache.olingo.server.api.uri.queryoption.expression.ExpressionVisitor</em>. </p>
+<p>As you mentioned the interface needs a generic parameter.
+This type is used as (return) parameter for the visitXXX methods (e.g. <em>visitLiteral</em> ). It`s up to your implementation to
+choose a proper type for your use case. The main task is to keep track of the type and also the return value of a node in the abstract syntax tree.
+In real world scenarios it is common to build a statement to query a database or backend instead modifying the preloaded data. </p>
+<p>In this tutorial we will use just <em>Object</em> and pass the native Java values around.</p>
+<div class="codehilite"><pre><span class="kd">public</span> <span class="kd">class</span> <span class="nc">FilterExpressionVisitor</span> <span class="kd">implements</span> <span class="n">ExpressionVisitor</span><span class="o"><</span><span class="n">Object</span><span class="o">></span> <span class="o">{</span>
+</pre></div>
+
+
+<p>Please create also a constructor to pass an entity to our visitor implementation.</p>
+<div class="codehilite"><pre><span class="kd">private</span> <span class="n">Entity</span> <span class="n">currentEntity</span><span class="o">;</span>
+
+<span class="kd">public</span> <span class="nf">FilterExpressionVisitor</span><span class="o">(</span><span class="n">Entity</span> <span class="n">currentEntity</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">this</span><span class="o">.</span><span class="na">currentEntity</span> <span class="o">=</span> <span class="n">currentEntity</span><span class="o">;</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<p><strong>1.2 Implement the interface</strong></p>
+<p>In this basic tutorial we will implement only a subset of the Expression Visitor.
+The following methods will <strong>not</strong> be implemented. Add an <em>ODataApplicationException</em> to their bodies</p>
+<ul>
+<li>public Object visitTypeLiteral(EdmType type)</li>
+<li>public Object visitAlias(String aliasName)</li>
+<li>public Object visitEnum(EdmEnumType type, List<String> enumValues)</li>
+<li>public Object visitLambdaExpression(String lambdaFunction, String lambdaVariable, Expression expression)</li>
+<li>public Object visitLambdaReference(String variableName)</li>
+</ul>
+<p><strong>Example</strong></p>
+<div class="codehilite"><pre><span class="nd">@Override</span>
+<span class="kd">public</span> <span class="n">Object</span> <span class="nf">visitTypeLiteral</span><span class="o">(</span><span class="n">EdmType</span> <span class="n">type</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ExpressionVisitException</span><span class="o">,</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Type literals are not implemented"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">NOT_IMPLEMENTED</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<p><strong>Implement method visitMember</strong><br />
+This method is been called if the current node in the AST is a property. So all we have to do is to take the current entity and return the value of the addressed property.</p>
+<div class="codehilite"><pre><span class="kd">public</span> <span class="n">Object</span> <span class="nf">visitMember</span><span class="o">(</span><span class="n">UriInfoResource</span> <span class="n">member</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ExpressionVisitException</span><span class="o">,</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+ <span class="c1">// To keeps things simple, this tutorial allows only primitive properties.</span>
+ <span class="c1">// We have faith that the java type of Edm.Int32 is Integer</span>
+ <span class="kd">final</span> <span class="n">List</span><span class="o"><</span><span class="n">UriResource</span><span class="o">></span> <span class="n">uriResourceParts</span> <span class="o">=</span> <span class="n">member</span><span class="o">.</span><span class="na">getUriResourceParts</span><span class="o">();</span>
+
+ <span class="c1">// Make sure that the resource path of the property contains only a single segment and a </span>
+ <span class="c1">// primitive property has been addressed. We can be sure, that the property exists because </span>
+ <span class="c1">// the UriParser checks if the property has been defined in service metadata document.</span>
+
+ <span class="k">if</span><span class="o">(</span><span class="n">uriResourceParts</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="n">uriResourceParts</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">instanceof</span> <span class="n">UriResourcePrimitiveProperty</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">UriResourcePrimitiveProperty</span> <span class="n">uriResourceProperty</span> <span class="o">=</span> <span class="o">(</span><span class="n">UriResourcePrimitiveProperty</span><span class="o">)</span> <span class="n">uriResourceParts</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">currentEntity</span><span class="o">.</span><span class="na">getProperty</span><span class="o">(</span><span class="n">uriResourceProperty</span><span class="o">.</span><span class="na">getProperty</span><span class="o">().</span><span class="na">getName</span><span class="o">()).</span><span class="na">getValue</span><span class="o">();</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="c1">// The OData specification allows in addition complex properties and navigation </span>
+ <span class="c1">// properties with a target cardinality 0..1 or 1.</span>
+ <span class="c1">// This means any combination can occur e.g. Supplier/Address/City</span>
+ <span class="c1">// -> Navigation properties Supplier </span>
+ <span class="c1">// -> Complex Property Address</span>
+ <span class="c1">// -> Primitive Property City</span>
+ <span class="c1">// For such cases the resource path returns a list of UriResourceParts</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Only primitive properties are implemented in filter </span>
+<span class="s"> expressions"</span><span class="o">,</span> <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">NOT_IMPLEMENTED</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<p><strong>Implement method visitLiteral</strong></p>
+<p>The next method takes a String and has to return the type and also the value of literal. </p>
+<p><strong>Example</strong> </p>
+<ul>
+<li>"â1â" is a string with the value "1"</li>
+<li>"1" could be an Byte, SByte, Edm.Int16, EdmInt32, EdmInt64, Edm.Single, Edm.Double, Edm.Decimal with value 1</li>
+</ul>
+<p>As you can see in this little example, it can be difficult to guess the right type. In this tutorial we will focus on Edm.Int32. </p>
+<p>In real world scenarios, there is something called ânumeric promotionâ, which converts numbers to the next highest type. <a href="http://docs.oasis-open.org/odata/odata/v4.0/errata02/os/complete/part2-url-conventions/odata-v4.0-errata02-os-part2-url-conventions-complete.html#_Toc406398161">OData Version 4.0 Part 2: URL Conventions Plus Errata 02</a></p>
+<div class="codehilite"><pre><span class="kd">public</span> <span class="n">Object</span> <span class="nf">visitLiteral</span><span class="o">(</span><span class="n">String</span> <span class="n">literal</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ExpressionVisitException</span><span class="o">,</span>
+ <span class="n">ODataApplicationException</span> <span class="o">{</span>
+ <span class="c1">// To keep this tutorial simple, our filter expression visitor supports only Edm.Int32 and Edm.String</span>
+ <span class="c1">// In real world scenarios it can be difficult to guess the type of an literal.</span>
+ <span class="c1">// We can be sure, that the literal is a valid OData literal because the URI Parser checks </span>
+ <span class="c1">// the lexicographical structure</span>
+
+ <span class="c1">// String literals start and end with an single quotation mark</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">literal</span><span class="o">.</span><span class="na">startsWith</span><span class="o">(</span><span class="s">"'"</span><span class="o">)</span> <span class="o">&&</span> <span class="n">literal</span><span class="o">.</span><span class="na">endsWith</span><span class="o">(</span><span class="s">"'"</span><span class="o">))</span> <span class="o">{</span>
+ <span class="n">String</span> <span class="n">stringLiteral</span> <span class="o">=</span> <span class="s">""</span><span class="o">;</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">literal</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">></span> <span class="mi">2</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">stringLiteral</span> <span class="o">=</span> <span class="n">literal</span><span class="o">.</span><span class="na">substring</span><span class="o">(</span><span class="mi">1</span><span class="o">,</span> <span class="n">literal</span><span class="o">.</span><span class="na">length</span><span class="o">()</span> <span class="o">-</span> <span class="mi">1</span><span class="o">);</span>
+ <span class="o">}</span>
+
+ <span class="k">return</span> <span class="n">stringLiteral</span><span class="o">;</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="c1">// Try to convert the literal into an Java Integer</span>
+ <span class="k">try</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="n">Integer</span><span class="o">.</span><span class="na">parseInt</span><span class="o">(</span><span class="n">literal</span><span class="o">);</span>
+ <span class="o">}</span> <span class="k">catch</span><span class="o">(</span><span class="n">NumberFormatException</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Only Edm.Int32 and Edm.String literals are </span>
+<span class="s"> implemented"</span><span class="o">,</span> <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">NOT_IMPLEMENTED</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+ <span class="o">}</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<p><strong>Implement the operators</strong></p>
+<p>The first two implemented methods dealt on the leaves of the AST. Now we will implement the operations, which can be performed on these values.</p>
+<p>The idea behind the implementation is always the same. </p>
+<ol>
+<li>Check if the types fit together</li>
+<li>If true => Calculate and return the result</li>
+<li>Otherwise => Throw an <em>ODataApplicationException</em> with StatusCode 400 Bad Request</li>
+</ol>
+<p>OData supports two different unary operators. First there is the binary negation (<em>not</em>) and second the arithmetic minus (<em>-</em>). </p>
+<div class="codehilite"><pre><span class="kd">public</span> <span class="n">Object</span> <span class="nf">visitUnaryOperator</span><span class="o">(</span><span class="n">UnaryOperatorKind</span> <span class="n">operator</span><span class="o">,</span> <span class="n">Object</span> <span class="n">operand</span><span class="o">)</span>
+ <span class="kd">throws</span> <span class="n">ExpressionVisitException</span><span class="o">,</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+ <span class="c1">// OData allows two different unary operators. We have to take care, that the type of the </span>
+ <span class="c1">// operand fits to the operand</span>
+
+ <span class="k">if</span><span class="o">(</span><span class="n">operator</span> <span class="o">==</span> <span class="n">UnaryOperatorKind</span><span class="o">.</span><span class="na">NOT</span> <span class="o">&&</span> <span class="n">operand</span> <span class="k">instanceof</span> <span class="n">Boolean</span><span class="o">)</span> <span class="o">{</span>
+ <span class="c1">// 1.) boolean negation </span>
+ <span class="k">return</span> <span class="o">!(</span><span class="n">Boolean</span><span class="o">)</span> <span class="n">operand</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">operator</span> <span class="o">==</span> <span class="n">UnaryOperatorKind</span><span class="o">.</span><span class="na">MINUS</span> <span class="o">&&</span> <span class="n">operand</span> <span class="k">instanceof</span> <span class="n">Integer</span><span class="o">){</span>
+ <span class="c1">// 2.) arithmetic minus</span>
+ <span class="k">return</span> <span class="o">-(</span><span class="n">Integer</span><span class="o">)</span> <span class="n">operand</span><span class="o">;</span>
+ <span class="o">}</span>
+
+ <span class="c1">// Operation not processed, throw an exception</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Invalid type for unary operator"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">BAD_REQUEST</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<p>Next are the binary operations. Have a look at the source code comments for a detailed explanation.´</p>
+<div class="codehilite"><pre><span class="nd">@Override</span>
+<span class="kd">public</span> <span class="n">Object</span> <span class="nf">visitBinaryOperator</span><span class="o">(</span><span class="n">BinaryOperatorKind</span> <span class="n">operator</span><span class="o">,</span> <span class="n">Object</span> <span class="n">left</span><span class="o">,</span> <span class="n">Object</span> <span class="n">right</span><span class="o">)</span>
+ <span class="kd">throws</span> <span class="n">ExpressionVisitException</span><span class="o">,</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+
+ <span class="c1">// Binary Operators are split up in three different kinds. Up to the kind of the </span>
+ <span class="c1">// operator it can be applied to different types</span>
+ <span class="c1">// - Arithmetic operations like add, minus, modulo, etc. are allowed on numeric </span>
+ <span class="c1">// types like Edm.Int32</span>
+ <span class="c1">// - Logical operations are allowed on numeric types and also Edm.String</span>
+ <span class="c1">// - Boolean operations like and, or are allowed on Edm.Boolean</span>
+ <span class="c1">// A detailed explanation can be found in OData Version 4.0 Part 2: URL Conventions</span>
+
+ <span class="k">if</span> <span class="o">(</span><span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">ADD</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">MOD</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">MUL</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">DIV</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">SUB</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="nf">evaluateArithmeticOperation</span><span class="o">(</span><span class="n">operator</span><span class="o">,</span> <span class="n">left</span><span class="o">,</span> <span class="n">right</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">EQ</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">NE</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">GE</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">GT</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">LE</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">LT</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="nf">evaluateComparisonOperation</span><span class="o">(</span><span class="n">operator</span><span class="o">,</span> <span class="n">left</span><span class="o">,</span> <span class="n">right</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">AND</span>
+ <span class="o">||</span> <span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">OR</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="nf">evaluateBooleanOperation</span><span class="o">(</span><span class="n">operator</span><span class="o">,</span> <span class="n">left</span><span class="o">,</span> <span class="n">right</span><span class="o">);</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Binary operation "</span> <span class="o">+</span> <span class="n">operator</span><span class="o">.</span><span class="na">name</span><span class="o">()</span> <span class="o">+</span> <span class="s">" is not </span>
+<span class="s"> implemented"</span><span class="o">,</span> <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">NOT_IMPLEMENTED</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+ <span class="o">}</span>
+
+<span class="kd">private</span> <span class="n">Object</span> <span class="nf">evaluateBooleanOperation</span><span class="o">(</span><span class="n">BinaryOperatorKind</span> <span class="n">operator</span><span class="o">,</span> <span class="n">Object</span> <span class="n">left</span><span class="o">,</span> <span class="n">Object</span> <span class="n">right</span><span class="o">)</span>
+ <span class="kd">throws</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+
+ <span class="c1">// First check that both operands are of type Boolean</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">left</span> <span class="k">instanceof</span> <span class="n">Boolean</span> <span class="o">&&</span> <span class="n">right</span> <span class="k">instanceof</span> <span class="n">Boolean</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">Boolean</span> <span class="n">valueLeft</span> <span class="o">=</span> <span class="o">(</span><span class="n">Boolean</span><span class="o">)</span> <span class="n">left</span><span class="o">;</span>
+ <span class="n">Boolean</span> <span class="n">valueRight</span> <span class="o">=</span> <span class="o">(</span><span class="n">Boolean</span><span class="o">)</span> <span class="n">right</span><span class="o">;</span>
+
+ <span class="c1">// Than calculate the result value</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">AND</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="n">valueLeft</span> <span class="o">&&</span> <span class="n">valueRight</span><span class="o">;</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="c1">// OR</span>
+ <span class="k">return</span> <span class="n">valueLeft</span> <span class="o">||</span> <span class="n">valueRight</span><span class="o">;</span>
+ <span class="o">}</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Boolean operations needs two numeric operands"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">BAD_REQUEST</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+<span class="o">}</span>
+
+<span class="kd">private</span> <span class="n">Object</span> <span class="nf">evaluateComparisonOperation</span><span class="o">(</span><span class="n">BinaryOperatorKind</span> <span class="n">operator</span><span class="o">,</span> <span class="n">Object</span> <span class="n">left</span><span class="o">,</span> <span class="n">Object</span> <span class="n">right</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+
+ <span class="c1">// All types in our tutorial supports all logical operations, but we have to make sure that </span>
+ <span class="c1">// the types are equal</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">left</span><span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">equals</span><span class="o">(</span><span class="n">right</span><span class="o">.</span><span class="na">getClass</span><span class="o">()))</span> <span class="o">{</span>
+ <span class="c1">// Luckily all used types String, Boolean and also Integer support the interface </span>
+ <span class="c1">// Comparable</span>
+ <span class="kt">int</span> <span class="n">result</span><span class="o">;</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">left</span> <span class="k">instanceof</span> <span class="n">Integer</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">result</span> <span class="o">=</span> <span class="o">((</span><span class="n">Comparable</span><span class="o"><</span><span class="n">Integer</span><span class="o">>)</span> <span class="o">(</span><span class="n">Integer</span><span class="o">)</span> <span class="n">left</span><span class="o">).</span><span class="na">compareTo</span><span class="o">((</span><span class="n">Integer</span><span class="o">)</span> <span class="n">right</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">left</span> <span class="k">instanceof</span> <span class="n">String</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">result</span> <span class="o">=</span> <span class="o">((</span><span class="n">Comparable</span><span class="o"><</span><span class="n">String</span><span class="o">>)</span> <span class="o">(</span><span class="n">String</span><span class="o">)</span> <span class="n">left</span><span class="o">).</span><span class="na">compareTo</span><span class="o">((</span><span class="n">String</span><span class="o">)</span> <span class="n">right</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">left</span> <span class="k">instanceof</span> <span class="n">Boolean</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">result</span> <span class="o">=</span> <span class="o">((</span><span class="n">Comparable</span><span class="o"><</span><span class="n">Boolean</span><span class="o">>)</span> <span class="o">(</span><span class="n">Boolean</span><span class="o">)</span> <span class="n">left</span><span class="o">).</span><span class="na">compareTo</span><span class="o">((</span><span class="n">Boolean</span><span class="o">)</span> <span class="n">right</span><span class="o">);</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Class "</span> <span class="o">+</span> <span class="n">left</span><span class="o">.</span><span class="na">getClass</span><span class="o">().</span><span class="na">getCanonicalName</span><span class="o">()</span> <span class="o">+</span> <span class="s">" not expected"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">INTERNAL_SERVER_ERROR</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+
+ <span class="k">if</span> <span class="o">(</span><span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">EQ</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="mi">0</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">NE</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="mi">0</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">GE</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="mi">0</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">GT</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="mi">0</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">LE</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="mi">0</span><span class="o">;</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="c1">// BinaryOperatorKind.LT</span>
+ <span class="k">return</span> <span class="n">result</span> <span class="o"><</span> <span class="mi">0</span><span class="o">;</span>
+ <span class="o">}</span>
+
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Comparision needs two equal types"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">BAD_REQUEST</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+<span class="o">}</span>
+
+<span class="kd">private</span> <span class="n">Object</span> <span class="nf">evaluateArithmeticOperation</span><span class="o">(</span><span class="n">BinaryOperatorKind</span> <span class="n">operator</span><span class="o">,</span> <span class="n">Object</span> <span class="n">left</span><span class="o">,</span>
+ <span class="n">Object</span> <span class="n">right</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+
+ <span class="c1">// First check if the type of both operands is numerical</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">left</span> <span class="k">instanceof</span> <span class="n">Integer</span> <span class="o">&&</span> <span class="n">right</span> <span class="k">instanceof</span> <span class="n">Integer</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">Integer</span> <span class="n">valueLeft</span> <span class="o">=</span> <span class="o">(</span><span class="n">Integer</span><span class="o">)</span> <span class="n">left</span><span class="o">;</span>
+ <span class="n">Integer</span> <span class="n">valueRight</span> <span class="o">=</span> <span class="o">(</span><span class="n">Integer</span><span class="o">)</span> <span class="n">right</span><span class="o">;</span>
+
+ <span class="c1">// Than calculate the result value</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">ADD</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="n">valueLeft</span> <span class="o">+</span> <span class="n">valueRight</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">SUB</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="n">valueLeft</span> <span class="o">-</span> <span class="n">valueRight</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">MUL</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="n">valueLeft</span> <span class="o">*</span> <span class="n">valueRight</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">operator</span> <span class="o">==</span> <span class="n">BinaryOperatorKind</span><span class="o">.</span><span class="na">DIV</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">return</span> <span class="n">valueLeft</span> <span class="o">/</span> <span class="n">valueRight</span><span class="o">;</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="c1">// BinaryOperatorKind,MOD</span>
+ <span class="k">return</span> <span class="n">valueLeft</span> <span class="o">%</span> <span class="n">valueRight</span><span class="o">;</span>
+ <span class="o">}</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Arithmetic operations needs two numeric </span>
+<span class="s"> operands"</span><span class="o">,</span> <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">BAD_REQUEST</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<p>The last method we have to implement is <em>visitMethodCall</em>. The principle is always the same, check the types and calculate the return value. As a developer you can be sure, that the number of parameters fits to the MethodKind but the types have to be checked by yourself. E.g. <em>contains</em> takes two Strings and return <em>Edm.Boolean</em> but </p>
+<div class="codehilite"><pre> $<span class="n">filter</span><span class="p">=</span><span class="n">contains</span><span class="p">(</span>123<span class="p">,</span>123<span class="p">)</span>
+</pre></div>
+
+
+<p>would not lead to an error. It`s up to you to throw an exception.</p>
+<div class="codehilite"><pre><span class="nd">@Override</span>
+<span class="kd">public</span> <span class="n">Object</span> <span class="nf">visitMethodCall</span><span class="o">(</span><span class="n">MethodKind</span> <span class="n">methodCall</span><span class="o">,</span> <span class="n">List</span><span class="o"><</span><span class="n">Object</span><span class="o">></span> <span class="n">parameters</span><span class="o">)</span>
+ <span class="kd">throws</span> <span class="n">ExpressionVisitException</span><span class="o">,</span> <span class="n">ODataApplicationException</span> <span class="o">{</span>
+
+ <span class="c1">// To keep this tutorial small and simple, we implement only one method call</span>
+ <span class="c1">// contains(String, String) -> Boolean</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">methodCall</span> <span class="o">==</span> <span class="n">MethodKind</span><span class="o">.</span><span class="na">CONTAINS</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">parameters</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">instanceof</span> <span class="n">String</span> <span class="o">&&</span> <span class="n">parameters</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="mi">1</span><span class="o">)</span> <span class="k">instanceof</span> <span class="n">String</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">String</span> <span class="n">valueParam1</span> <span class="o">=</span> <span class="o">(</span><span class="n">String</span><span class="o">)</span> <span class="n">parameters</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">String</span> <span class="n">valueParam2</span> <span class="o">=</span> <span class="o">(</span><span class="n">String</span><span class="o">)</span> <span class="n">parameters</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="mi">1</span><span class="o">);</span>
+
+ <span class="k">return</span> <span class="n">valueParam1</span><span class="o">.</span><span class="na">contains</span><span class="o">(</span><span class="n">valueParam2</span><span class="o">);</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Contains needs two parametes of type Edm.String"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">BAD_REQUEST</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Method call "</span> <span class="o">+</span> <span class="n">methodCall</span> <span class="o">+</span> <span class="s">" not implemented"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">NOT_IMPLEMENTED</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<p><strong>2. EntityCollectionProcessor changes</strong>*</p>
+<p>The following section describes the simple approach to enable the EntityCollectionProcessor class and the readEntityCollection() method for $filter.</p>
+<p>Just like in the previous tutorials, the data is first fetched from the backend, then the system query option is applied.</p>
+<div class="codehilite"><pre><span class="n">EntityCollection</span> <span class="n">entityCollection</span> <span class="o">=</span> <span class="n">storage</span><span class="o">.</span><span class="na">readEntitySetData</span><span class="o">(</span><span class="n">edmEntitySet</span><span class="o">);</span>
+<span class="n">List</span><span class="o"><</span><span class="n">Entity</span><span class="o">></span> <span class="n">entityList</span> <span class="o">=</span> <span class="n">entityCollection</span><span class="o">.</span><span class="na">getEntities</span><span class="o">();</span>
+</pre></div>
+
+
+<p>We will proceed according to these 4 steps:</p>
+<ol>
+<li>Get the query option from the UriInfo. If null is returned then nothing has to be done. </li>
+<li>Get the expression from the query option </li>
+<li>Instantiate our Expression Visitor and evaluate the result for each entity in the collection</li>
+<li>Modify the EntityCollection based on the result of the expression</li>
+</ol>
+<p><strong>2.1 Get the FilterOption from the uriInfo</strong></p>
+<div class="codehilite"><pre><span class="n">FilterOption</span> <span class="n">filterOption</span> <span class="p">=</span> <span class="n">uriInfo</span><span class="p">.</span><span class="n">getFilterOption</span><span class="p">();</span>
+<span class="k">if</span><span class="p">(</span><span class="n">filterOption</span> !<span class="p">=</span> <span class="n">null</span><span class="p">)</span> <span class="p">{</span>
+</pre></div>
+
+
+<p><strong>2.2 Get the expression from the query option</strong></p>
+<div class="codehilite"><pre><span class="n">Expression</span> <span class="n">filterExpression</span> <span class="p">=</span> <span class="n">filterOption</span><span class="p">.</span><span class="n">getExpression</span><span class="p">();</span>
+</pre></div>
+
+
+<p><strong>2.3 Loop over all entities in the collection and calculate the result of the expression for a given entity</strong></p>
+<div class="codehilite"><pre><span class="k">try</span> <span class="o">{</span>
+ <span class="n">List</span><span class="o"><</span><span class="n">Entity</span><span class="o">></span> <span class="n">entityList</span> <span class="o">=</span> <span class="n">entityCollection</span><span class="o">.</span><span class="na">getEntities</span><span class="o">();</span>
+ <span class="n">Iterator</span><span class="o"><</span><span class="n">Entity</span><span class="o">></span> <span class="n">entityIterator</span> <span class="o">=</span> <span class="n">entityList</span><span class="o">.</span><span class="na">iterator</span><span class="o">();</span>
+
+ <span class="c1">// Evaluate the expression for each entity</span>
+ <span class="c1">// If the expression is evaluated to "true", keep the entity otherwise remove it from </span>
+ <span class="c1">// the entityList</span>
+ <span class="k">while</span> <span class="o">(</span><span class="n">entityIterator</span><span class="o">.</span><span class="na">hasNext</span><span class="o">())</span> <span class="o">{</span>
+ <span class="c1">// To evaluate the the expression, create an instance of the Filter Expression </span>
+ <span class="c1">// Visitor and pass the current entity to the constructor</span>
+ <span class="n">Entity</span> <span class="n">currentEntity</span> <span class="o">=</span> <span class="n">entityIterator</span><span class="o">.</span><span class="na">next</span><span class="o">();</span>
+ <span class="n">FilterExpressionVisitor</span> <span class="n">expressionVisitor</span> <span class="o">=</span> <span class="k">new</span> <span class="n">FilterExpressionVisitor</span><span class="o">(</span><span class="n">currentEntity</span><span class="o">);</span>
+
+ <span class="c1">// Evaluating the expression</span>
+ <span class="n">Object</span> <span class="n">visitorResult</span> <span class="o">=</span> <span class="n">filterExpression</span><span class="o">.</span><span class="na">accept</span><span class="o">(</span><span class="n">expressionVisitor</span><span class="o">);</span>
+ <span class="err">â¦</span>
+</pre></div>
+
+
+<p><strong>2.4 Modify the collection</strong> </p>
+<div class="codehilite"><pre> <span class="c1">// The result of the filter expression must be of type Edm.Boolean</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">visitorResult</span> <span class="k">instanceof</span> <span class="n">Boolean</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">if</span><span class="o">(</span><span class="n">visitorResult</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&&</span> <span class="n">Boolean</span><span class="o">.</span><span class="na">FALSE</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">visitorResult</span><span class="o">))</span> <span class="o">{</span>
+ <span class="c1">// The expression evaluated to false, so we have to remove the </span>
+ <span class="c1">// currentEntity from entityList</span>
+ <span class="n">entityIterator</span><span class="o">.</span><span class="na">remove</span><span class="o">();</span>
+ <span class="o">}</span>
+ <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"A filter expression must evaulate to type Edm.Boolean"</span><span class="o">,</span> <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">BAD_REQUEST</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+ <span class="o">}</span>
+ <span class="o">}</span> <span class="c1">// End while</span>
+<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">ExpressionVisitException</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">throw</span> <span class="k">new</span> <span class="nf">ODataApplicationException</span><span class="o">(</span><span class="s">"Exception in filter evaluation"</span><span class="o">,</span>
+ <span class="n">HttpStatusCode</span><span class="o">.</span><span class="na">INTERNAL_SERVER_ERROR</span><span class="o">.</span><span class="na">getStatusCode</span><span class="o">(),</span> <span class="n">Locale</span><span class="o">.</span><span class="na">ENGLISH</span><span class="o">);</span>
+<span class="o">}</span>
+</pre></div>
+
+
+<h3 id="3-run-the-implemented-service">3. Run the implemented service<a class="headerlink" href="#3-run-the-implemented-service" title="Permanent link">¶</a></h3>
+<p>After building and deploying your service to your server, you can try the following URLs:</p>
+<p><strong>Comparison operators</strong></p>
+<ul>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID eq 1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID eq 1</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID ne 1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID ne 1</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID gt 2">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID gt 2</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID ge 2">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID ge 2</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID le 2">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID le 2</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID lt 2">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID lt 2</a></li>
+</ul>
+<p><strong>Unary operators</strong></p>
+<ul>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=-ID eq -1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=-ID eq -1</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=not(ID eq 1)">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=not(ID eq 1)</a></li>
+</ul>
+<p><strong>Method calls and strong binding unary not</strong></p>
+<ul>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo')">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo')</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=not contains(Name,'Ergo')">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=not contains(Name,'Ergo')</a></li>
+</ul>
+<p><strong>Arithmetic operators</strong></p>
+<ul>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID add 1 eq 2">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID add 1 eq 2</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID sub 1 eq 1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID sub 1 eq 1</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID div 2 eq 1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID div 2 eq 1</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID mul 2 eq 6">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID mul 2 eq 6</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID mod 2 eq 1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=ID mod 2 eq 1</a></li>
+</ul>
+<p><strong>String literal</strong></p>
+<ul>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=Name eq" title="1UMTS PDA">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=Name eq '1UMTS PDA'</a></li>
+</ul>
+<p><strong>Boolean operators</strong></p>
+<ul>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo') or ID eq 1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo') or ID eq 1</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo') and ID eq 1">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo') and ID eq 1</a></li>
+<li><a href="http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo') and ID eq 3">http://localhost:8080/DemoService/DemoService.svc/Products?$filter=contains(Name,'Ergo') and ID eq 3</a></li>
+</ul>
+<h2 id="summary">Summary<a class="headerlink" href="#summary" title="Permanent link">¶</a></h2>
+<p>In this tutorial we have learned how to implement a simple service with $filter system query option. The very same Expression Visitor can be used to support advanced $orderby query options. The main difference is that, the Expression Visitor used by $orderby returns a (may be calculated) value of a primitive property instead a Boolean value.</p>
+<h2 id="links">Links<a class="headerlink" href="#links" title="Permanent link">¶</a></h2>
+<h3 id="tutorials">Tutorials<a class="headerlink" href="#tutorials" title="Permanent link">¶</a></h3>
+<ul>
+<li>Tutorial OData V4 service part 1: <a href="/doc/odata4/tutorials/read/tutorial_read.html">Read Entity Collection</a> | <a href="http://www.apache.org/dyn/closer.cgi/olingo/odata4/Tutorials/DemoService_Tutorial_Read.zip">sample project</a> (<a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Read.zip.md5">md5</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Read.zip.sha512">sha512</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Read.zip.asc">pgp</a>).</li>
+<li>Tutorial OData V4 service part 2: <a href="/doc/odata4/tutorials/readep/tutorial_readep.html">Read Entity, Read Property</a> | <a href="http://www.apache.org/dyn/closer.cgi/olingo/odata4/Tutorials/DemoService_Tutorial_ReadEp.zip">sample project zip</a> (<a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_ReadEp.zip.md5">md5</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_ReadEp.zip.sha512">sha512</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_ReadEp.zip.asc">pgp</a>) </li>
+<li>Tutorial OData V4 service part 3: <a href="/doc/odata4/tutorials/write/tutorial_write.html">Write (Create, Update, Delete Entity)</a> | <a href="http://www.apache.org/dyn/closer.cgi/olingo/odata4/Tutorials/DemoService_Tutorial_Write.zip">sample project zip</a> (<a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Write.zip.md5">md5</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Write.zip.sha512">sha512</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Write.zip.asc">pgp</a>) </li>
+<li>Tutorial OData V4 service, part 4: <a href="/doc/odata4/tutorials/navigation/tutorial_navigation.html">Navigation</a> | <a href="http://www.apache.org/dyn/closer.cgi/olingo/odata4/Tutorials/DemoService_Tutorial_Navigation.zip">sample project zip</a> (<a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Navigation.zip.md5">md5</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Navigation.zip.sha512">sha512</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_Navigation.zip.asc">pgp</a>)</li>
+<li>Tutorial OData V4 service, part 5.1: <a href="/doc/odata4/tutorials/sqo_tcs/tutorial_sqo_tcs.html">System Query Options $top, $skip, $count (this page)</a> | <a href="http://www.apache.org/dyn/closer.cgi/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_tcs.zip">sample project zip</a> (<a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_tcs.zip.md5">md5</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_tcs.zip.sha512">sha512</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_tcs.zip.asc">pgp</a>) </li>
+<li>Tutorial OData V4 service, part 5.2: <a href="/doc/odata4/tutorials/sqo_es/tutorial_sqo_es.html">System Query Options $select, $expand</a> | <a href="http://www.apache.org/dyn/closer.cgi/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_es.zip">sample project zip</a> (<a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_es.zip.md5">md5</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_es.zip.sha512">sha512</a>, <a href="https://dist.apache.org/repos/dist/release/olingo/odata4/Tutorials/DemoService_Tutorial_sqo_es.zip.asc">pgp</a>) </li>
+<li>Tutorial OData V4 service, part 5.3: <a href="/doc/odata4/tutorials/sqo_o/tutorial_sqo_o.html">System Query Options $orderby</a></li>
+<li>Tutorial OData V4 service, part 5.4: System Query Options $filter (this page)</li>
+</ul>
+<h3 id="further-reading">Further reading<a class="headerlink" href="#further-reading" title="Permanent link">¶</a></h3>
+<ul>
+<li><a href="http://odata.org/">Official OData Homepage</a></li>
+<li><a href="http://www.odata.org/documentation/">OData documentation</a></li>
+<li><a href="/javadoc/odata4/index.html">Olingo Javadoc</a></li>
+</ul><div align="center">
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