183 lines
8.2 KiB
HTML
183 lines
8.2 KiB
HTML
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<title>Strolch: Searches</title>
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<div class="page-header">
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<h1 class="page-title">Documentation: Searches</h1>
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<p class="lead page-description">This page discusses Strolch Searches.</p>
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<div class="content">
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<p>As is custom for every framework, querying, or searching, the model must be possible. Strolch searches are
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implemented using the <code>StrolchSearch</code> class and one of its concrete implementations: <code>ResourceSearch</code>,
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<code>OrderSearch</code>, <code>ActivitySearch</code>.</p>
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<p>A Strolch element always has two identifiers: <code>Type</code> and <code>Id</code>. The type is important as
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it classifies an element. So if a car and a house would be modelled in Strolch, then those would both be a
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<code>Resource</code>, but one of type <code>Car</code> and the other of type <code>House</code>. Both would
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have different parameters. Thus when searching for objects, the first thing to do is define the type of
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object being searched.</p>
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<p>The Strolch search API is very expressive and offers multiple ways to perform the same search. The search API
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consists of three components: The search classes, the search expressions and the search predicates. The
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concept was taken from the <a href="https://camel.apache.org" target="_blank">Apache Camel</a> project.</p>
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<p>There are four main search classes:</p>
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<ul>
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<li><code>RootElementSearch</code> - search for any of <code>Resource</code>, <code>Order</code> or <code>Activity</code>
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elements
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</li>
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<li><code>ResourceSearch</code> - search for <code>Resources</code></li>
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<li><code>OrderSearch</code> - search for <code>Orders</code></li>
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<li><code>ActivitySearch</code> - search for <code>Activities</code></li>
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</ul>
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<p>No search is useful without a <code>where</code> clause, which are called search expressions. When writing a
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search, there are multiple ways to add such where clauses. Either</p>
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<ul>
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<li>override the <code>define()</code> method in your sub class and add the where clauses by calling the
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<code>where()</code> method, or
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</li>
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<li>define special methods on the class e.g. <code>byColor()</code> which also calls the
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<code>where()</code> method to add a search expression, or
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</li>
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<li>directly call the <code>where()</code> method after instantiating a search.</li>
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</ul>
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<p>When extending the class, then the search expressions are available as methods on the super class, otherwise
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you can statically import them from
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<a href="https://github.com/4treesCH/strolch/blob/develop/li.strolch.agent/src/main/java/li/strolch/search/ExpressionsSupport.java"
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target="_blank">ExpressionsSupport</a>.</p>
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<p>And of course a where clause needs operators, which are called search predicates. Just as search expressions
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are available in sub classes, so are search predicates and can also be statically imported through
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<a href="https://github.com/4treesCH/strolch/blob/develop/li.strolch.agent/src/main/java/li/strolch/search/PredicatesSupport.java"
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target="_blank">PredicatesSupport</a>.</p>
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<p>Examples of search expressions with search predicates follow:</p>
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<pre>
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ResourceSearch search = new ResourceSearch();
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// predicate either as parameter, or chained
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search.where(id().isEqualTo("myId"));
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search.where(id(isEqualTo("myId")));
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// negating
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search.where(id(isEqualTo("myId")).not());
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search.where(param("bagId", "paramId").isIn(Arrays.asList("red", "blue", "green")));
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search.where(paramNull("bagId", "paramId")));
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// boolean operations
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search.where(id(isEqualTo("myId")) //
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.or(name(isEqualTo("myName"))));
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</pre>
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<p>Note how the predicates can be chained to the search expression, or passed as a parameter to the
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expression.</p>
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<p>In addition to using predefined search search expressions, one can also just pass a lambda expression which
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performs a custom filter:</p>
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<pre>
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personSearch.where(person -> person.getName().length() == 3);</pre>
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<p>See the
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<a href="https://github.com/4treesCH/strolch/blob/develop/li.strolch.agent/src/test/java/li/strolch/search/StrolchSearchTest.java"
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target="_blank">StrolchSearchTest</a> for many ways in which you can implement tests.</p>
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<p>Note that strolch searches requires privileges. Thus when you use a strolch search, add it to the role of the
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user in <code>PrivilegeRoles.xml</code>:</p>
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<pre>
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<Privilege name="li.strolch.search.StrolchSearch" policy="DefaultPrivilege">
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<Allow>internal</Allow> <!-- internal used for when the search is done in an internal service -->
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<Allow>li.strolch.bookshop.search.BookSearch</Allow>
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</Privilege></pre>
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<a href="http://www.eitchnet.ch">eitchnet.ch</a></p>
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