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<h1 class="post-title-main">Signal enrichment</h1>
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<p><a href="basic-signals.html">Signals</a> which are emitted to subscribers via <a href="httpapi-protocol-bindings-websocket.html">WebSocket API</a>,
<a href="httpapi-sse.html">HTTP SSEs</a> or established <a href="basic-connections.html">connections</a> may be enriched
by <code class="highlighter-rouge">extraFields</code> to also be included in the sent out messages.</p>
<p><a href="basic-signals-event.html">Events</a>, for example, only contain the actually changed data by default, so when they are
subscribed to via one of the APIs listed above, the data they contain may be as sparse as:
“temperature value was changed to 23.4 for thing with ID xx”.</p>
<p>Often it is helpful to additionally include some extra fields as context to be included when subscribing
(e.g. via WebSocket or a connection). For example in order to include static metadata stored in the <code class="highlighter-rouge">attributes</code>.</p>
<p>Therefore it is possible to define <code class="highlighter-rouge">extraFields</code> to include when subscribing for:</p>
<ul>
<li><a href="basic-changenotifications.html">events/change notifications</a></li>
<li><a href="basic-messages.html">messages</a></li>
<li><a href="protocol-twinlive.html">live commands</a></li>
<li><a href="protocol-twinlive.html">live events</a></li>
</ul>
<p>How the <code class="highlighter-rouge">extraFields</code> are specified is depending on the API, please find the specific API information here:</p>
<ul>
<li><a href="httpapi-protocol-bindings-websocket.html#enrichment">WebSocket enrichment</a></li>
<li><a href="httpapi-sse.html#field-enrichment">SSE field enrichment</a></li>
<li><a href="basic-connections.html#target-topics-and-enrichment">Connection target enrichment</a></li>
</ul>
<p>The <code class="highlighter-rouge">extra</code> data is added to the <a href="protocol-specification.html#extra">extra field in Ditto Protocol messages</a> being an
JSON object containing all selected fields.</p>
<h2 id="example">Example</h2>
<p>For example a Thing could look like this:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"thingId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"org.eclipse.ditto:fancy-thing"</span><span class="p">,</span><span class="w">
</span><span class="s2">"policyId"</span><span class="p">:</span><span class="w"> </span><span class="s2">"org.eclipse.ditto:fancy-thing"</span><span class="p">,</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"location"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Kitchen"</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"temperature"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"value"</span><span class="p">:</span><span class="w"> </span><span class="mf">23.42</span><span class="p">,</span><span class="w">
</span><span class="s2">"unit"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Celcius"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>Now whenever its temperature is modified you normally only get the following information in the event
(this is a <a href="protocol-specification.html">Ditto Protocol</a> message):</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"topic"</span><span class="p">:</span><span class="w"> </span><span class="s2">"org.eclipse.ditto/fancy-thing/things/twin/events/modified"</span><span class="p">,</span><span class="w">
</span><span class="s2">"headers"</span><span class="p">:</span><span class="w"> </span><span class="p">{},</span><span class="w">
</span><span class="s2">"path"</span><span class="p">:</span><span class="w"> </span><span class="s2">"/features/temperature/properties/value"</span><span class="p">,</span><span class="w">
</span><span class="s2">"value"</span><span class="p">:</span><span class="w"> </span><span class="mf">23.42</span><span class="p">,</span><span class="w">
</span><span class="s2">"revision"</span><span class="p">:</span><span class="w"> </span><span class="mi">34</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<p>What you could want is to:</p>
<ul>
<li>additionally add the <code class="highlighter-rouge">attributes</code></li>
<li>additionally add the <code class="highlighter-rouge">unit</code> value of the temperature</li>
</ul>
<p>In that case you would define to include <code class="highlighter-rouge">extraFields</code>
(syntax is the same as for retrieving partial things with <a href="httpapi-concepts.html#with-field-selector">field selector</a>):</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>extraFields=attributes,features/temperature/properties/unit
</code></pre></div></div>
<p>In that case, each emitted Ditto Protocol event would include an <code class="highlighter-rouge">extra</code> section containing the selected data:</p>
<div class="language-json highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="p">{</span><span class="w">
</span><span class="s2">"topic"</span><span class="p">:</span><span class="w"> </span><span class="s2">"org.eclipse.ditto/fancy-thing/things/twin/events/modified"</span><span class="p">,</span><span class="w">
</span><span class="s2">"headers"</span><span class="p">:</span><span class="w"> </span><span class="p">{},</span><span class="w">
</span><span class="s2">"path"</span><span class="p">:</span><span class="w"> </span><span class="s2">"/features/temperature/properties/value"</span><span class="p">,</span><span class="w">
</span><span class="s2">"value"</span><span class="p">:</span><span class="w"> </span><span class="mf">23.42</span><span class="p">,</span><span class="w">
</span><span class="s2">"revision"</span><span class="p">:</span><span class="w"> </span><span class="mi">34</span><span class="p">,</span><span class="w">
</span><span class="s2">"extra"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"attributes"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"location"</span><span class="p">:</span><span class="w"> </span><span class="s2">"kitchen"</span><span class="w">
</span><span class="p">},</span><span class="w">
</span><span class="s2">"features"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"temperature"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"properties"</span><span class="p">:</span><span class="w"> </span><span class="p">{</span><span class="w">
</span><span class="s2">"unit"</span><span class="p">:</span><span class="w"> </span><span class="s2">"Celcius"</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span><span class="p">}</span><span class="w">
</span></code></pre></div></div>
<h2 id="enrich-and-filter">Enrich and filter</h2>
<p>In combination with <a href="basic-changenotifications.html#filtering">event filtering</a> enriched data can also be used to
filter. For example, when selecting <code class="highlighter-rouge">extraFields=attributes/location</code>, an additional <code class="highlighter-rouge">filter</code> may define to only
emit events for a certain location: <code class="highlighter-rouge">extraFields=attributes/location&amp;filter=eq(attributes/location,"kitchen")</code>.</p>
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