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<div class="section" id="utility-registration-apis">
<h1>Utility Registration APIs<a class="headerlink" href="#utility-registration-apis" title="Permalink to this headline">¶</a></h1>
<p>Utilities are components that simply provide an interface. They are
instantiated at the time or before they are registered. Here we test the
simple query interface.</p>
<p>Before we register any utility, there is no utility available, of
course. The pure instatiation of an object does not make it a utility. If
you do not specify a default, you get a <cite>ComponentLookupError</cite>.</p>
<p>Otherwise, you get the default:</p>
<p>Now we declare <cite>ob</cite> to be the utility providing <cite>I1</cite>:</p>
<p>Now the component is available:</p>
<div class="section" id="named-utilities">
<h2>Named Utilities<a class="headerlink" href="#named-utilities" title="Permalink to this headline">¶</a></h2>
<p>Registering a utility without a name does not mean that it is available
when looking for the utility with a name:</p>
<p>Registering the utility under the correct name makes it available:</p>
</div>
<div class="section" id="querying-multiple-utilities">
<h2>Querying Multiple Utilities<a class="headerlink" href="#querying-multiple-utilities" title="Permalink to this headline">¶</a></h2>
<p>Sometimes it may be useful to query all utilities, both anonymous and named
for a given interface. The <code class="xref py py-func docutils literal notranslate"><span class="pre">getUtilitiesFor()</span></code> API
returns a sequence of <code class="docutils literal notranslate"><span class="pre">(name,</span> <span class="pre">utility)</span></code> tuples, where <code class="docutils literal notranslate"><span class="pre">name</span></code> is the
empty string for the anonymous utility:</p>
<p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">getAllUtilitiesRegisteredFor()</span></code> API returns
utilities that have been registered for a particular interface. Utilities
providing a derived interface are also listed.</p>
<p>Now we register the new utilities:</p>
<p>We can now get all the utilities that provide interface <cite>I1</cite>:</p>
<p>Note that <cite>getAllUtilitiesRegisteredFor()</cite> does not return the names of
the utilities.</p>
</div>
<div class="section" id="delegated-utility-lookup">
<h2>Delegated Utility Lookup<a class="headerlink" href="#delegated-utility-lookup" title="Permalink to this headline">¶</a></h2>
<p>It is common for a utility to delegate its answer to a utility
providing the same interface in one of the component registry’s
bases. Let’s first create a global utility:</p>
<p>Now, let’s create two registries and set up the bases hierarchy:</p>
<p>Now we create two utilities and insert them in our folder hierarchy:</p>
<p>Now, if we ask <cite>util1_1</cite> for its next available utility we get the
<code class="docutils literal notranslate"><span class="pre">one</span></code> utility:</p>
<p>Next we ask <cite>util1</cite> for its next utility and we should get the global version:</p>
<p>However, if we ask the global utility for the next one, an error is raised</p>
<p>You can also use <cite>queryNextUtility</cite> and specify a default:</p>
<p>Let’s now ensure that the function also works with multiple registries. First
we create another base registry:</p>
<p>We now set up another utility into that registry:</p>
<p>We add it as a base to the local site manager:</p>
<p>Both the <code class="docutils literal notranslate"><span class="pre">myregistry</span></code> and global utilities should be available:</p>
<p>Note, if the context cannot be converted to a site manager, the default is
retruned:</p>
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