Elasticsearch indexed search template generates empty strings in array

I've seen this requirement before and the solution looks hacky, but it works. Basically, the commas in the template are the problem because Mustache will go over the array and for each element in the array will put the element - {{.}} - but also the comma you are specifying inside {{#myTerms}} and {{/myTerms}}.

And, also, in your case you shouldn't use double quotes - "{{.}}" because the element itself will be surrounded with double quotes. That's why you are seeing "1" in the result. But, if you want to match numbers that should be a list of numbers, not strings.

So, first of all, get rid of the double quotes. This means, surrounding the template with double quotes and escape any double quotes that should make it in the final result (you'll understand shortly by seeing the example below).

Secondly, the hacky part is to simulate the commas in the result and to skip the last comma. Meaning, 1,2,3, shouldn't contain the last comma. The solution is to provide the parameters as a list of tuples - one element of the tuple is the value itself, the other element is a boolean: [{"value":1,"comma":true},{"value":2,"comma":true},{"value":4}]. If comma is true then Mustache should put the ,, otherwise not (this case is for the last element in the array).

POST /_search/template/myTemplate{"template":"{\"filter\":{\"bool\":{\"must\":[{\"terms\":{\"myTerms\":[{{#myTerms}}{{value}}{{#comma}},{{/comma}}{{/myTerms}}],\"_cache\":true}}]}}}"}

And this is how you should pass the parameters:

{  "template": {    "id": "myTemplate"  },  "params": {    "myTerms": [{"value":1,"comma":true},{"value":2,"comma":true},{"value":4}]  }}

What this does is to generate something like this:

{  "filter": {    "bool": {      "must": [        {          "terms": {            "myTerms": [1,2,4],            "_cache": true          }        }      ]    }  }}