title: Extract json string field in Google Data Studio
body: <p>I'm trying to analyze my Firestore data in Google Data Studio. I have successfully imported my data from BigQuery to Google Data Studio, but I'm not unable to use it.</p>
  <p>Here is my JSON format in GDS :</p>
  <pre><code>{
      &quot;document_name&quot;: &quot;projects/path&quot;,
      &quot;document_id&quot;: &quot;01ASsoYefmYy4h8mGTPWzt5d5Xw1&quot;,
      &quot;timestamp&quot;: &quot;1970-01-01 00:00:00 UTC&quot;,
      &quot;event_id&quot;: &quot;&quot;,
      &quot;operation&quot;: &quot;IMPORT&quot;,
      &quot;data&quot;: &quot;{\&quot;mail\&quot;:\&quot;email@gmail.com\&quot;,\&quot;creationDate\&quot;:1602011942852,\&quot;initialized\&quot;:true,\&quot;languageCode\&quot;:\&quot;en\&quot;}&quot;
  }
  </code></pre>
  <p>I'm trying to use the <strong>creationDate</strong> or the <strong>mail</strong> as field but I'm unable to create a field with this because this is a stringified JSON.
  I tried to find a solution with formula, without success.</p>
  <p>How to exploit field in stringified JSON in Google Data Studio ?</p>
  <p>Thanks</p>