# \_source filtering in field collapsing query

**URL:** <https://discuss.elastic.co/t/-source-filtering-in-field-collapsing-query/81255>\
**Category:** Elasticsearch\
**Created:** [April 5, 2017, 6:40am UTC](https://discuss.elastic.co/t/-source-filtering-in-field-collapsing-query/81255 "2017-04-05T06:40:54Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Youxu](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/youxu/32/117375_2.png) [@Youxu](https://discuss.elastic.co/u/Youxu)\
**Post date:** [April 5, 2017, 6:40am UTC](https://discuss.elastic.co/t/-source-filtering-in-field-collapsing-query/81255/1 "2017-04-05T06:40:54Z")

</div>

I tried field collapsing query with following query DSL:

```auto
{
    "query": {
        "match": {
            "Title": "elasticsearch"
        }
    },
    "collapse" : {
        "field" : "Category",
        "inner_hits": {
            "_source": ["Title", "Url"]
            "name": "top_docs", 
            "size": 10
        }
    }    
}

```

But got following error message:

```auto
 "reason": "[collapse] failed to parse field [inner_hits]",
    "line": 10,
    "col": 24,
    "caused_by": {
      "type": "illegal_argument_exception",
      "reason": "[inner_hits] _source doesn't support values of type: START_ARRAY"
    }

```

Per [https://www.elastic.co/guide/en/elasticsearch/reference/5.3/search-request-inner-hits.html](https://www.elastic.co/guide/en/elasticsearch/reference/5.3/search-request-inner-hits.html), source filtering is supported in inner\_hits options.

Anything wrong in my DSL?

---

<div class="post-metadata">

**Author:** ![Youxu](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/youxu/32/117375_2.png) [@Youxu](https://discuss.elastic.co/u/Youxu)\
**Post date:** [April 5, 2017, 6:46am UTC](https://discuss.elastic.co/t/-source-filtering-in-field-collapsing-query/81255/2 "2017-04-05T06:46:50Z")

</div>

I found the solution myself.

If using source filtering in inner\_hits, I must use "include“ pattern as follows:

```auto
{
    "query": {
        "match": {
            "Title": "birds"
        }
    },
    "collapse" : {
        "field" : "Category.raw",
        "inner_hits": {
            "_source": {
                "include": ["Title", "Url"]
            },
            "name": "top_docs", 
            "size": 10
        }
    }    
}

```

Is it by design or a bug?

Anyway, it should be clearly stated in document.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [May 3, 2017, 6:47am UTC](https://discuss.elastic.co/t/-source-filtering-in-field-collapsing-query/81255/3 "2017-05-03T06:47:24Z")

</div>

Closed on May 3, 2017, 6:47am UTC

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