Renaming fields in elasticsearch
<p>I have a document like this</p>

<pre><code>{
    "_index": "testindex",
    "_type": "logs",
    "_id": "1",
    "_score": 1,
    "_source": {
      "field1": "data1",
      "field2": "data2"
    }
}
</code></pre>

<p>I need to change the <code>field2</code> to <code>Request.field3</code></p>

<pre><code>{
    "_index": "testindex",
    "_type": "logs",
    "_id": "1",
    "_score": 1,
    "_source": {
      "field1": "data1",
      "Request": {
        "field3": "data2"
      }
    }
}
</code></pre>

<p>For this, first added a field mapping to existing index</p>

<pre><code>PUT testindex/_mapping/logs
{
    "properties": 
    { 
        "Request": 
        {
            "properties": 
            {
                "field3" : 
                {
                    "type": "string"
                }
            }
        }   
    }  
}
</code></pre>

<p>Then tried reindexing</p>

<pre><code>POST _reindex
{
    "source": {
        "index": "testindex"
    },
    "dest": {
        "index": "testindex1"
    },
    "script": {
        "inline": "ctx._source.Request.field3 = ctx._source.remove(\"field2\")"
    }
}
</code></pre>

<p>Error is</p>

<pre><code>"reason": "failed to run inline script [ctx._source.Request.field3 = ctx._source.remove(\"field2\")] using lang [groovy]",
"caused_by": {
    "type": "null_pointer_exception",
    "reason": "Cannot set property 'field3' on null object"
}
</code></pre>