title: Elasticsearch version 7 cannot be changed from type [keyword] to [text]
body: <p>I am a newbie of elasticsearch. I create a mapping using such code:</p>
  <pre class="lang-json prettyprint-override"><code>PUT /my-demo1
  {
    &quot;mappings&quot;: {
      &quot;properties&quot;: {
        &quot;dsu_sn&quot;: {
          &quot;type&quot;: &quot;keyword&quot;
        },
        &quot;iot_id&quot;: {
          &quot;type&quot;: &quot;keyword&quot;
        },
        &quot;test_suite_id&quot;: {
          &quot;type&quot;: &quot;text&quot;
        },
        &quot;error_code&quot;: {
          &quot;type&quot;: &quot;long&quot;
        }
      }
    }
  }
  </code></pre>
  <p>ES responses <code>mapper [iot_id] cannot be changed from type [keyword] to [text]</code> when I index a document using such code:</p>
  <pre class="lang-json prettyprint-override"><code>POST /my-demo1/1
  {
    &quot;dsu_sn&quot;: &quot;ssl123321&quot;,
    &quot;iot_id&quot;: &quot;550068573720395776&quot;,
    &quot;test_suite_id&quot;: &quot;com.example.test.wifi&quot;,
    &quot;error_code&quot;: 2
  }
  </code></pre>