What is the best way to use mustache False values feature in Elasticsearch template?

At the moment I am trying to select function based on boolean value. Rendering seems to be working according to the logic, but it prints empty double quotes and I cannot get rid of those.

Code example mustache template snippet:

                "must": {
                    "function_score": {
                        "functions": [
                            "{{^isLocationFunctionNeeded}}",
                            {
                                "exp": {
                                    "location": {
                                        "origin": {
                                            "lat": "0.0",
                                            "lon": "0.0"
                                        },
                                        "offset": "1km",
                                        "scale": "50km"
                                    }
                                }
                            },
                            "{{/isLocationFunctionNeeded}}",
                            {
                                "random_score": {},
                                "weight": 0.00001
                            }
                        ],
                        "score_mode": "sum"
                    }
                }

Render snippet:

 "must": {
                "function_score": {
                    "functions": [
                        "",
                        {
                            "random_score": {},
                            "weight": 1.0E-5
                        }
                    ],
                    "score_mode": "sum"
                }
            }

Error I get trying to run the template on ELK:

    "error": {
        "root_cause": [
            {
                "type": "parsing_exception",
                "reason": "failed to parse [START_OBJECT]. malformed query, expected a [VALUE_STRING] while parsing functions but got a [function_score] instead",
                "line": x (where "" is visible in Render snippet),
                "col": x (where "" is visible in Render snippet)
            }
        ],
"type": "x_content_parse_exception",
        "reason": " x (where "" is visible in Render snippet),[bool] failed to parse field [must]",
        "caused_by": {
            "type": "parsing_exception",
            "reason": "failed to parse [START_OBJECT]. malformed query, expected a [VALUE_STRING] while parsing functions but got a [function_score] instead",
            "line":  x (where "" is visible in Render snippet),,
            "col":  x (where "" is visible in Render snippet),
        }

Without mustache values it's working fine. Also I noticed in some cases if you surround empty double quotes with random functions it tends to work sometimes. Seems Elastic don't like must cases starting with empty double quotes.

I also asked the same question in ELK community with no luck so far: https://discuss.elastic.co/t/mustache-double-quotes-problem-in-search-templates/318736

As an example for rendering template we can try using the following:

{
    "script": {
        "lang": "mustache",
        "source": {
            "must": {
                "function_score": {
                    "functions": [
                        "{{^isLocationFunctionNeeded}}",
                        {
                            "exp": {
                                "location": {
                                    "lat": "0.0",
                                    "lon": "0.0"
                                },
                                "offset": "1km",
                                "scale": "50km"
                            }
                        },
                        "{{/isLocationFunctionNeeded}}",
                        {
                            "random_score": {},
                            "weight": 0.00001
                        }
                    ],
                    "score_mode": "sum"
                }
            }
        }
    }
}

Calling template with params:

{
    "id": "example_template",
    "params": {
    "isLocationFunctionNeeded" : true
    }
}

CodePudding user response：

The query inside your template must be a full fledge query, not just must. Also you need to enclose it in triple quotes """, like this, and it will work

POST _scripts/example_template
{
  "script": {
    "lang": "mustache",
    "source": """
      {
        "query": {
          "bool": {
            "must": {
              "function_score": {
                "functions": [
                  {{^isLocationFunctionNeeded}}
                  {
                    "exp": {
                      "location": {
                        "lat": "0.0",
                        "lon": "0.0"
                      },
                      "offset": "1km",
                      "scale": "50km"
                    }
                  },
                  {{/isLocationFunctionNeeded}}
                  {
                    "random_score": {},
                    "weight": 0.00001
                  }
                ],
                "score_mode": "sum"
              }
            }
          }
        }
      }
    """
  }
}

If you cannot use the triple quotes (e.g. when using Postman), you need to send it as a one-line string and escape all quote characters:

POST _scripts/example_template
{
  "script": {
    "lang": "mustache",
    "source": " { \"query\": { \"bool\": { \"must\": { \"function_score\": { \"functions\": [ {{^isLocationFunctionNeeded}} { \"exp\": { \"location\": { \"lat\": \"0.0\",  \"lon\": \"0.0\" }, \"offset\": \"1km\", \"scale\": \"50km\" } }, {{/isLocationFunctionNeeded}} { \"random_score\": {}, \"weight\": 0.00001 } ], \"score_mode\": \"sum\" }}}}"
  }
}