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<h1 class="post-title-main">RQL expressions</h1>
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<p>Ditto utilizes a subset of <a href="#" data-toggle="tooltip" data-original-title="Resource Query Language">RQL</a>
as language for specifying queries.</p>
<p>The <a href="https://github.com/persvr/rql">RQL project page</a> says about it:</p>
<blockquote>
<p>Resource Query Language (RQL) is a query language designed for use in URIs with object style data structures. […]<br />
RQL can be thought as basically a set of nestable named operators which each have a set of arguments.
RQL is designed to have an extremely simple, but extensible grammar that can be written in a URL friendly query string.</p>
</blockquote>
<p>An example helps more than a thousand words, so that would be the example of a simple RQL query querying for <code class="highlighter-rouge">foo="ditto"</code> and <code class="highlighter-rouge">bar&lt;10</code>:</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>and(eq(foo,"ditto"),lt(bar,10))
</code></pre></div></div>
<p>That query consists of one <a href="#logical-operators">logical operator </a> <a href="#and">“and”</a>,
two <a href="#relational-operators">relational operators</a> of which each consists of a <a href="#query-property">property</a>
and a <a href="#query-value">value</a>.</p>
<p>The following sections describe what the RQL syntax is capable of.</p>
<h2 id="rql-filter">RQL filter</h2>
<p>The RQL filter specifies “what” to filter.</p>
<h3 id="query-property">Query property</h3>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>&lt;property&gt; = url-encoded-string
</code></pre></div></div>
<p>To filter nested properties, Ditto uses the JSON Pointer notation (<a href="https://tools.ietf.org/html/rfc6901">RFC-6901</a>).</p>
<p>The following example shows how to apply a filter for the sub property location of the parent property attributes with
a forward slash as separator:</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>eq(attributes/location,"kitchen")
</code></pre></div></div>
<h3 id="query-value">Query value</h3>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>&lt;value&gt; = &lt;number&gt;, &lt;string&gt;, true, false, null
&lt;number&gt; = double, integer
&lt;string&gt; = ", url-encoded-string, "
</code></pre></div></div>
<p><strong>Comparison of string values</strong></p>
<div class="alert alert-info" role="alert"><i class="fa fa-info-circle"></i> <b>Note:</b> Comparison operators such as <code class="highlighter-rouge">gt</code>, <code class="highlighter-rouge">ge</code>, <code class="highlighter-rouge">lt</code> and <code class="highlighter-rouge">le</code>, do not support a special
“semantics” of string comparison (e.g. regarding alphabetical or lexicographical ordering).<br />
However, you can rely on the alphabetical sorting of strings with the same length (e.g. “aaa” &lt; “zzz”) and that the
order stays the same over multiple/different filter requests.</div>
<p><strong>Comparison of other data types</strong></p>
<div class="alert alert-info" role="alert"><i class="fa fa-info-circle"></i> <b>Note:</b> Please note that the comparison of other data types is is supported by the API, but it
only supports comparison of same data types, and does not do any conversion during comparison.</div>
<h3 id="relational-operators">Relational operators</h3>
<p>The following relational operators are supported.</p>
<h4 id="eq">eq</h4>
<p>Filter property values equal to <code class="highlighter-rouge">&lt;value&gt;</code>.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>eq(&lt;property&gt;,&lt;value&gt;)
</code></pre></div></div>
<p><strong>Example - filter things owned by “SID123”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>eq(attributes/owner,"SID123")
</code></pre></div></div>
<h4 id="ne">ne</h4>
<p>Filter property values not equal to <code class="highlighter-rouge">&lt;value&gt;</code>.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>ne(&lt;property&gt;,&lt;value&gt;)
</code></pre></div></div>
<p><strong>Example - filter things with owner different than “SID123”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>ne(attributes/owner,"SID123")
</code></pre></div></div>
<p>The response will contain only things which <strong>do</strong> provide an owner attribute (in this case with value 0 or not SID123).</p>
<h4 id="gt">gt</h4>
<p>Filter property values greater than a <code class="highlighter-rouge">&lt;value&gt;</code>.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>gt(&lt;property&gt;,&lt;value&gt;)
</code></pre></div></div>
<p><strong>Example - filter things with thing ID greater than “A000”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>gt(thingId,"A000")
</code></pre></div></div>
<h4 id="ge">ge</h4>
<p>Filter property values greater than or equal to a <code class="highlighter-rouge">&lt;value&gt;</code>.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>ge(&lt;property&gt;,&lt;value&gt;)
</code></pre></div></div>
<p><strong>Example - filter things with thing ID “A000” or greater</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>ge(thingId,"A000")
</code></pre></div></div>
<h4 id="lt">lt</h4>
<p>Filter property values less than a <code class="highlighter-rouge">&lt;value&gt;</code>.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>lt(&lt;property&gt;,&lt;value&gt;)
</code></pre></div></div>
<p><strong>Example - filter things with thing ID lower than “A000”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>lt(thingId,"A000")
</code></pre></div></div>
<h4 id="le">le</h4>
<p>Filter property values less than or equal to a <code class="highlighter-rouge">&lt;value&gt;</code>.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>le(&lt;property&gt;,&lt;value&gt;)
</code></pre></div></div>
<p><strong>Example - filter things with thing ID “A000” or lower</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>le(thingId,"A000")
</code></pre></div></div>
<h4 id="in">in</h4>
<p>Filter property values which contains at least one of the listed <code class="highlighter-rouge">&lt;value&gt;</code>s.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>in(&lt;property&gt;,&lt;value&gt;,&lt;value&gt;, ...)
</code></pre></div></div>
<p><strong>Example - filter things with thing ID “A000” or “AB00” or “AZ99”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>in(thingId,"A000","AB00","AZ99")
</code></pre></div></div>
<h4 id="like">like</h4>
<p>Filter property values which are like (similar) a <code class="highlighter-rouge">&lt;value&gt;</code>.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>like(&lt;property&gt;,&lt;value&gt;)
</code></pre></div></div>
<p><strong>Details concerning the like-operator</strong></p>
<p>The <code class="highlighter-rouge">like</code> operator provides some regular expression capabilities for pattern matching Strings.<br />
The following expressions are supported:</p>
<ul>
<li>*endswith =&gt; match at the end of a specific String.</li>
<li>startswith* =&gt; match at the beginning of a specific String.</li>
<li>*contains* =&gt; match if contains a specific String.</li>
<li>Th?ng =&gt; match for a wildcard character.</li>
</ul>
<p><strong>Examples</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>like(attributes/key1,"*known-chars-at-end")
like(attributes/key1,"known-chars-at-start*")
like(attributes/key1,"*known-chars-in-between*")
like(attributes/key1,"just-som?-char?-unkn?wn")
</code></pre></div></div>
<h4 id="exists">exists</h4>
<p>Filter property values which exist.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>exists(&lt;property&gt;)
</code></pre></div></div>
<p><strong>Example - filter things which have a feature with ID “feature_1”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>exists(features/feature_1)
</code></pre></div></div>
<p><strong>Example - filter lamps which are located in the “living-room”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>and(exists(features/lamp),eq(attributes/location,"living-room"))
</code></pre></div></div>
<h3 id="logical-operators">Logical operators</h3>
<h4 id="and">and</h4>
<p>Ensure that all given queries match.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>and(&lt;query&gt;,&lt;query&gt;, ...)
</code></pre></div></div>
<p><strong>Example - filter things which are located on the “upper floor” in the “living-room”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>and(eq(attributes/floor,"upper floor"),eq(attributes/location,"living-room"))
</code></pre></div></div>
<h4 id="or">or</h4>
<p>At least one of the given queries match.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>or(&lt;query&gt;,&lt;query&gt;, ...)
</code></pre></div></div>
<p><strong>Example - filter all things located on the “upper floor”, and all things with location “living-room”</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>or(eq(attributes/floor,"upper floor"),eq(attributes/location,"living-room"))
</code></pre></div></div>
<h4 id="not">not</h4>
<p>Negates the given query.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>not(&lt;query&gt;)
</code></pre></div></div>
<p><strong>Example - filter things whose ID do not start with a common prefix</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>not(like(thingId,"org.eclipse.ditto:blocked*"))
</code></pre></div></div>
<h2 id="rql-sorting">RQL sorting</h2>
<p>The RQL sorting part specifies in which order the result should be returned.</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sort(&lt;+|-&gt;&lt;property&gt;,&lt;+|-&gt;&lt;property&gt;,...)
</code></pre></div></div>
<ul>
<li>Use <strong>+</strong> for an ascending sort order (URL encoded character <strong>%2B</strong>)</li>
<li>Use <strong>-</strong> for a descending sort order (URL encoded character <strong>%2D</strong>)</li>
</ul>
<p><strong>Example - sort the list ascending by the thing ID</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sort(+thingId)
</code></pre></div></div>
<p><strong>Example - sort the list ascending by an attribute</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sort(+attributes/location)
</code></pre></div></div>
<p><strong>Example - multiple sort options</strong></p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sort(-attributes/location,+thingId)
</code></pre></div></div>
<p>This expression will sort the list descending by location attribute.<br />
In case there are multiple things with the same location attribute, these are sorted ascending by their ID.</p>
<h3 id="sorting-of-string-values">Sorting of string values</h3>
<div class="alert alert-info" role="alert"><i class="fa fa-info-circle"></i> <b>Note:</b> Sorting does not support a special “semantics” of string comparison (e.g. regarding
alphabetical or lexicographical ordering). However, you can rely on the alphabetical sorting of strings with the
same length (e.g. “aaa” &lt; “zzz”) and that the order stays the same over multiple/different filter requests.</div>
<h3 id="sorting-of-other-values">Sorting of other values</h3>
<div class="alert alert-info" role="alert"><i class="fa fa-info-circle"></i> <b>Note:</b> Sorting does not support a special “semantics” of comparison for fields with values of
different data types (e.g. numbers vs. strings). However, you can rely on the fact that values of the same type are
sorted respectively.</div>
<div class="tags">
<b>Tags: </b>
<a href="tag_rql.html" class="btn btn-default navbar-btn cursorNorm" role="button">rql</a>
<a href="tag_protocol.html" class="btn btn-default navbar-btn cursorNorm" role="button">protocol</a>
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