如何用php查询elasticsearch中的嵌入字段？

How can I query filename from my index. using multi_match I can query "content" by adding it to the fields query.

'query' => $q,
'fields' => ['content']

But I also want the filename value which is nested inside file (I am using fscrawler).. kindly advice.

"content": "REPORT ON PyCON 2017,
    ..
    ..
    .. ",

"file": {
    "extension": "docx",                        
    "filesize": 5468,
    "filename": "REPORT ON PyCON 2017.docx",
    "url": "file:///tmp/es/REPORT ON PyCON 2017.docx"
},