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<h1 id="json-flatten-spec">JSON Flatten Spec</h1>
<table><thead>
<tr>
<th>Field</th>
<th>Type</th>
<th>Description</th>
<th>Required</th>
</tr>
</thead><tbody>
<tr>
<td>useFieldDiscovery</td>
<td>Boolean</td>
<td>If true, interpret all fields with singular values (not a map or list) and flat lists (lists of singular values) at the root level as columns.</td>
<td>no (default == true)</td>
</tr>
<tr>
<td>fields</td>
<td>JSON Object array</td>
<td>Specifies the fields of interest and how they are accessed</td>
<td>no (default == [])</td>
</tr>
</tbody></table>
<p>Defining the JSON Flatten Spec allows nested JSON fields to be flattened during ingestion time. Only parseSpecs of types &quot;json&quot; or <a href="../development/extensions-core/avro.html">&quot;avro&quot;</a> support flattening.</p>
<p>&#39;fields&#39; is a list of JSON Objects, describing the field names and how the fields are accessed:</p>
<h2 id="json-field-spec">JSON Field Spec</h2>
<table><thead>
<tr>
<th>Field</th>
<th>Type</th>
<th>Description</th>
<th>Required</th>
</tr>
</thead><tbody>
<tr>
<td>type</td>
<td>String</td>
<td>Type of the field, &quot;root&quot;, &quot;path&quot; or &quot;jq&quot;.</td>
<td>yes</td>
</tr>
<tr>
<td>name</td>
<td>String</td>
<td>This string will be used as the column name when the data has been ingested.</td>
<td>yes</td>
</tr>
<tr>
<td>expr</td>
<td>String</td>
<td>Defines an expression for accessing the field within the JSON object, using <a href="https://github.com/jayway/JsonPath">JsonPath</a> notation for type &quot;path&quot;, and <a href="https://github.com/eiiches/jackson-jq">jackson-jq</a> for type &quot;jq&quot;. This field is only used for type &quot;path&quot; and &quot;jq&quot;, otherwise ignored.</td>
<td>only for type &quot;path&quot; or &quot;jq&quot;</td>
</tr>
</tbody></table>
<p>Suppose the event JSON has the following form:</p>
<div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="p">{</span>
<span class="nt">&quot;timestamp&quot;</span><span class="p">:</span> <span class="s2">&quot;2015-09-12T12:10:53.155Z&quot;</span><span class="p">,</span>
<span class="nt">&quot;dim1&quot;</span><span class="p">:</span> <span class="s2">&quot;qwerty&quot;</span><span class="p">,</span>
<span class="nt">&quot;dim2&quot;</span><span class="p">:</span> <span class="s2">&quot;asdf&quot;</span><span class="p">,</span>
<span class="nt">&quot;dim3&quot;</span><span class="p">:</span> <span class="s2">&quot;zxcv&quot;</span><span class="p">,</span>
<span class="nt">&quot;ignore_me&quot;</span><span class="p">:</span> <span class="s2">&quot;ignore this&quot;</span><span class="p">,</span>
<span class="nt">&quot;metrica&quot;</span><span class="p">:</span> <span class="mi">9999</span><span class="p">,</span>
<span class="nt">&quot;foo&quot;</span><span class="p">:</span> <span class="p">{</span><span class="nt">&quot;bar&quot;</span><span class="p">:</span> <span class="s2">&quot;abc&quot;</span><span class="p">},</span>
<span class="nt">&quot;foo.bar&quot;</span><span class="p">:</span> <span class="s2">&quot;def&quot;</span><span class="p">,</span>
<span class="nt">&quot;nestmet&quot;</span><span class="p">:</span> <span class="p">{</span><span class="nt">&quot;val&quot;</span><span class="p">:</span> <span class="mi">42</span><span class="p">},</span>
<span class="nt">&quot;hello&quot;</span><span class="p">:</span> <span class="p">[</span><span class="mf">1.0</span><span class="p">,</span> <span class="mf">2.0</span><span class="p">,</span> <span class="mf">3.0</span><span class="p">,</span> <span class="mf">4.0</span><span class="p">,</span> <span class="mf">5.0</span><span class="p">],</span>
<span class="nt">&quot;mixarray&quot;</span><span class="p">:</span> <span class="p">[</span><span class="mf">1.0</span><span class="p">,</span> <span class="mf">2.0</span><span class="p">,</span> <span class="mf">3.0</span><span class="p">,</span> <span class="mf">4.0</span><span class="p">,</span> <span class="p">{</span><span class="nt">&quot;last&quot;</span><span class="p">:</span> <span class="mi">5</span><span class="p">}],</span>
<span class="nt">&quot;world&quot;</span><span class="p">:</span> <span class="p">[{</span><span class="nt">&quot;hey&quot;</span><span class="p">:</span> <span class="s2">&quot;there&quot;</span><span class="p">},</span> <span class="p">{</span><span class="nt">&quot;tree&quot;</span><span class="p">:</span> <span class="s2">&quot;apple&quot;</span><span class="p">}],</span>
<span class="nt">&quot;thing&quot;</span><span class="p">:</span> <span class="p">{</span><span class="nt">&quot;food&quot;</span><span class="p">:</span> <span class="p">[</span><span class="s2">&quot;sandwich&quot;</span><span class="p">,</span> <span class="s2">&quot;pizza&quot;</span><span class="p">]}</span>
<span class="p">}</span>
</code></pre></div>
<p>The column &quot;metrica&quot; is a Long metric column, &quot;hello&quot; is an array of Double metrics, and &quot;nestmet.val&quot; is a nested Long metric. All other columns are dimensions.</p>
<p>To flatten this JSON, the parseSpec could be defined as follows:</p>
<div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="s2">&quot;parseSpec&quot;</span><span class="err">:</span> <span class="p">{</span>
<span class="nt">&quot;format&quot;</span><span class="p">:</span> <span class="s2">&quot;json&quot;</span><span class="p">,</span>
<span class="nt">&quot;flattenSpec&quot;</span><span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;useFieldDiscovery&quot;</span><span class="p">:</span> <span class="kc">true</span><span class="p">,</span>
<span class="nt">&quot;fields&quot;</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;root&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;dim1&quot;</span>
<span class="p">},</span>
<span class="s2">&quot;dim2&quot;</span><span class="p">,</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;foo.bar&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.foo.bar&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;root&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;foo.bar&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;path-metric&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.nestmet.val&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;hello-0&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.hello[0]&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;hello-4&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.hello[4]&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;world-hey&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.world[0].hey&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;worldtree&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.world[1].tree&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;first-food&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.thing.food[0]&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;path&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;second-food&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;$.thing.food[1]&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;jq&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;first-food-by-jq&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;.thing.food[1]&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span><span class="p">:</span> <span class="s2">&quot;jq&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;hello-total&quot;</span><span class="p">,</span>
<span class="nt">&quot;expr&quot;</span><span class="p">:</span> <span class="s2">&quot;.hello | sum&quot;</span>
<span class="p">}</span>
<span class="p">]</span>
<span class="p">},</span>
<span class="nt">&quot;dimensionsSpec&quot;</span> <span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;dimensions&quot;</span> <span class="p">:</span> <span class="p">[],</span>
<span class="nt">&quot;dimensionsExclusions&quot;</span><span class="p">:</span> <span class="p">[</span><span class="s2">&quot;ignore_me&quot;</span><span class="p">]</span>
<span class="p">},</span>
<span class="nt">&quot;timestampSpec&quot;</span> <span class="p">:</span> <span class="p">{</span>
<span class="nt">&quot;format&quot;</span> <span class="p">:</span> <span class="s2">&quot;auto&quot;</span><span class="p">,</span>
<span class="nt">&quot;column&quot;</span> <span class="p">:</span> <span class="s2">&quot;timestamp&quot;</span>
<span class="p">}</span>
<span class="p">}</span>
</code></pre></div>
<p>Fields &quot;dim3&quot;, &quot;ignore_me&quot;, and &quot;metrica&quot; will be automatically discovered because &#39;useFieldDiscovery&#39; is true, so they have been omitted from the field spec list.</p>
<p>&quot;ignore_me&quot; will be automatically discovered but excluded as specified by dimensionsExclusions.</p>
<p>Aggregators should use the metric column names as defined in the flattenSpec. Using the example above:</p>
<div class="highlight"><pre><code class="language-json" data-lang="json"><span></span><span class="s2">&quot;metricsSpec&quot;</span> <span class="err">:</span> <span class="p">[</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span> <span class="p">:</span> <span class="s2">&quot;longSum&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span> <span class="p">:</span> <span class="s2">&quot;path-metric-sum&quot;</span><span class="p">,</span>
<span class="nt">&quot;fieldName&quot;</span> <span class="p">:</span> <span class="s2">&quot;path-metric&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span> <span class="p">:</span> <span class="s2">&quot;doubleSum&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span> <span class="p">:</span> <span class="s2">&quot;hello-0-sum&quot;</span><span class="p">,</span>
<span class="nt">&quot;fieldName&quot;</span> <span class="p">:</span> <span class="s2">&quot;hello-0&quot;</span>
<span class="p">},</span>
<span class="p">{</span>
<span class="nt">&quot;type&quot;</span> <span class="p">:</span> <span class="s2">&quot;longSum&quot;</span><span class="p">,</span>
<span class="nt">&quot;name&quot;</span> <span class="p">:</span> <span class="s2">&quot;metrica-sum&quot;</span><span class="p">,</span>
<span class="nt">&quot;fieldName&quot;</span> <span class="p">:</span> <span class="s2">&quot;metrica&quot;</span>
<span class="p">}</span>
<span class="p">]</span>
</code></pre></div>
<p>Note that:</p>
<ul>
<li>For convenience, when defining a root-level field, it is possible to define only the field name, as a string, shown with &quot;dim2&quot; above.</li>
<li>Enabling &#39;useFieldDiscovery&#39; will only autodetect fields at the root level with a single value (not a map or list), as well as fields referring to a list of single values. In the example above, &quot;dim1&quot;, &quot;dim2&quot;, &quot;dim3&quot;, &quot;ignore_me&quot;, &quot;metrica&quot;, and &quot;foo.bar&quot; (at the root) would be automatically detected as columns. The &quot;hello&quot; field is a list of Doubles and will be autodiscovered, but note that the example ingests the individual list members as separate fields. The &quot;world&quot; field must be explicitly defined because its value is a map. The &quot;mixarray&quot; field, while similar to &quot;hello&quot;, must also be explicitly defined because its last value is a map.<br></li>
<li>Duplicate field definitions are not allowed, an exception will be thrown.</li>
<li>If auto field discovery is enabled, any discovered field with the same name as one already defined in the field specs will be skipped and not added twice.</li>
<li>The JSON input must be a JSON object at the root, not an array. e.g., {&quot;valid&quot;: &quot;true&quot;} and {&quot;valid&quot;:[1,2,3]} are supported but [{&quot;invalid&quot;: &quot;true&quot;}] and [1,2,3] are not.</li>
<li><a href="http://jsonpath.herokuapp.com/">http://jsonpath.herokuapp.com/</a> is useful for testing the path expressions.</li>
<li>jackson-jq supports subset of <a href="https://stedolan.github.io/jq/">./jq</a> syntax. Please refer jackson-jq document.</li>
</ul>
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