# Issue Using project Field in \_msearch with Siren Federate

**URL:** <https://community.siren.io/t/issue-using-project-field-in-msearch-with-siren-federate/775>\
**Category:** Siren Federate (Elasticsearch Plugin)\
**Created:** [December 11, 2025, 10:33am UTC](https://community.siren.io/t/issue-using-project-field-in-msearch-with-siren-federate/775 "2025-12-11T10:33:10Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Sayad\_Aazami](https://yyz2.discourse-cdn.com/flex032/user_avatar/community.siren.io/sayad_aazami/32/345_2.png) [@Sayad\_Aazami](https://community.siren.io/u/Sayad_Aazami)\
**Post date:** [December 11, 2025, 10:33am UTC](https://community.siren.io/t/issue-using-project-field-in-msearch-with-siren-federate/775/1 "2025-12-11T10:33:10Z")

</div>

Hi,  
I’m using the Siren Federate plugin and encountering an issue with multi-search (`_msearch`) queries.

When I use a regular `_search` query, I can `project` fields without any problems. However, when I use the same query in `_msearch`, I get the following error:

```auto
{ "index": "user" }
{ "size": 0, "track_total_hits": true, "query": { "bool": { "filter": [{ "bool": { "must": [ { "query_string": { "query": "_exists_:link" } }] } }, { "bool": { "must": [{ "join": { "indices": [ "user_info"], "on": ["id", "id"], "request": { "query": { "bool": { "must_not": [{ "ids": { "values": [ "123"] } } ] } }, "project": [{ "field": { "name": "_score", "alias": "sub_score" } }] } } } ] } } ], "must": [{ "function_score": { "functions": [ { "field_value_factor": { "field": "sub_score", "factor": 1, "missing": 1 } }] } } ] } } }

```

```auto
{
  "error": {
    "root_cause": [
      {
        "type": "parsing_exception",
        "reason": "Unknown key for a START_ARRAY in [project].",
        "line": 824,
        "col": 52
      }
    ],
    "type": "x_content_parse_exception",
    "reason": "[824:52] [bool] failed to parse field [filter]",
    "caused_by": {
      "type": "x_content_parse_exception",
      "reason": "[824:52] [bool] failed to parse field [must]",
      "caused_by": {
        "type": "parsing_exception",
        "reason": "Unknown key for a START_ARRAY in [project].",
        "line": 824,
        "col": 52
      }
    }
  },
  "status": 400
}

```

I wanted to ask if `projection` in `_msearch` requires a special structure or has any limitations, or if this might be an issue with the Siren Federate plugin itself.

Any guidance or example queries would be greatly appreciated.

---

<div class="post-metadata">

**Author:** ![Stephane\_Campinas](https://yyz2.discourse-cdn.com/flex032/user_avatar/community.siren.io/stephane_campinas/32/22_2.png) [@Stephane\_Campinas](https://community.siren.io/u/Stephane_Campinas)\
**Post date:** [December 11, 2025, 11:58am UTC](https://community.siren.io/t/issue-using-project-field-in-msearch-with-siren-federate/775/2 "2025-12-11T11:58:34Z")

</div>

Hello,

There is indeed a bug with msearch. Until the fix is there, just wrap the `project` into an `ext` yourself. See edited request:

```json
{"index":"user"}
{"size":0,"track_total_hits":true,"query":{"bool":{"filter":[{"bool":{"must":[{"query_string":{"query":"_exists_:link"}}]}},{"bool":{"must":[{"join":{"indices":["user_info"],"on":["id","id"],"request":{"query":{"bool":{"must_not":[{"ids":{"values":["123"]}}]}},"ext":{"project":[{"field":{"name":"_score","alias":"sub_score"}}]}}}}]}}],"must":[{"function_score":{"functions":[{"field_value_factor":{"field":"sub_score","factor":1,"missing":1}}]}}]}}}

```

Thanks for bringing this to our attention!

---

<div class="post-metadata">

**Author:** ![Sayad\_Aazami](https://yyz2.discourse-cdn.com/flex032/user_avatar/community.siren.io/sayad_aazami/32/345_2.png) [@Sayad\_Aazami](https://community.siren.io/u/Sayad_Aazami)\
**Post date:** [December 11, 2025, 12:11pm UTC](https://community.siren.io/t/issue-using-project-field-in-msearch-with-siren-federate/775/3 "2025-12-11T12:11:57Z")

</div>

> [@Stephane\_Campinas](#):
>
> `ext`

Hi again, dear friend!  
It worked  
I can’t tell you how helpful this was. I really, really appreciate it.

---

<div class="post-metadata">

**Author:** ![Stephane\_Campinas](https://yyz2.discourse-cdn.com/flex032/user_avatar/community.siren.io/stephane_campinas/32/22_2.png) [@Stephane\_Campinas](https://community.siren.io/u/Stephane_Campinas)\
**Post date:** [January 15, 2026, 10:15am UTC](https://community.siren.io/t/issue-using-project-field-in-msearch-with-siren-federate/775/4 "2026-01-15T10:15:35Z")

</div>

A fix is available in the 39 release [Downloads - SIREN](https://siren.io/downloads/?product=siren-federate) of Federate