[[search-template]]
== Search Template

coming[1.1.0]

Using a query template allows to use the mustache language to pre render search requests,
before they are executed and fill existing templates with template parameters.

You can use the `/_search/template` endpoint for that.

[source,js]
------------------------------------------
GET /_search/template
{
    "template" : {
      "query": { "match" : { "{{my_field}}" : "{{my_value}}" } },
      "size" : {{my_size}}
    },
    "params" : {
        "my_field" : "foo",
        "my_value" : "bar",
        "my_size" : 5
    }
}
------------------------------------------


For more information on how Mustache templating and what kind of templating you
can do with it check out the http://mustache.github.io/mustache.5.html[online
documentation of the mustache project].

[float]
==== More template examples

[float]
===== Filling in a query string with a single value

[source,js]
------------------------------------------
GET /_search/template
{
    "template": {
        "query": {
            "match": {
                "title": "{{query_string}}"
            }
        }
    },
    "params": {
        "query_string": "search for these words"
    }
}
------------------------------------------

[float]
===== Passing an array of strings

[source,js]
------------------------------------------
GET /_search/template
{
  "template": {
    "query": {
      "terms": {
        "status": [
          "{{#status}}",
          "{{.}}",
          "{{/status}}"
        ]
      }
    }
  },
  "params": {
    "status": [ "pending", "published" ]
  }
}
------------------------------------------

which is rendered as:

[source,js]
------------------------------------------
{
"query": {
  "terms": {
    "status": [ "pending", "published" ]
  }
}
------------------------------------------

[float]
===== Default values

A default value is written as `{{var}}{{^var}}default{{/var}}` for instance:

[source,js]
------------------------------------------
{
  "template": {
    "query": {
      "range": {
        "line_no": {
          "gte": "{{start}}",
          "lte": "{{end}}{{^end}}20{{/end}}"
        }
      }
    }
  },
  "params": { ... }
}
------------------------------------------

When `params` is `{ "start": 10, "end": 15 }` this query would be rendered as:

[source,js]
------------------------------------------
{
    "range": {
        "line_no": {
            "gte": "10",
            "lte": "15"
        }
  }
}
------------------------------------------

But when `params` is `{ "start": 10 }` this query would use the default value
for `end`:

[source,js]
------------------------------------------
{
    "range": {
        "line_no": {
            "gte": "10",
            "lte": "20"
        }
    }
}
------------------------------------------

[float]
===== Conditional clauses

Conditional clauses cannot be expressed using the JSON form of the template.
Instead, the template *must* be passed as a string.  For instance, let's say
we wanted to run a `match` query on the `line` field, and optionally wanted
to filter by line numbers, where `start` and `end` are optional.

The `params` would look like:
[source,js]
------------------------------------------
{
    "params": {
        "text":      "words to search for",
        "line_no": { <1>
            "start": 10, <1>
            "end":   20  <1>
        }
    }
}
------------------------------------------
<1> All three of these elements are optional.

We could write the query as:

[source,js]
------------------------------------------
{
    "filtered": {
      "query": {
        "match": {
          "line": "{{text}}" <1>
        }
      },
      "filter": {
        {{#line_no}} <2>
          "range": {
            "line_no": {
              {{#start}} <3>
                "gte": "{{start}}" <4>
                {{#end}},{{/end}} <5>
              {{/start}} <3>
              {{#end}} <6>
                "lte": "{{end}}" <7>
              {{/end}} </6>
            }
          }
        {{/line_no}} <2>
      }
    }
}
------------------------------------------
<1> Fill in the value of param `text`
<2> Include the `range` filter only if `line_no` is specified
<3> Include the `gte` clause only if `line_no.start` is specified
<4> Fill in the value of param `line_no.start`
<5> Add a comma after the `gte` clause only if `line_no.start`
    AND `line_no.end` are specified
<6> Include the `lte` clause only if `line_no.end` is specified
<7> Fill in the value of param `line_no.end`

As written above, this template is not valid JSON because it includes the
_section_ markers like `{{#line_no}}`.  For this reason, the template
can only be written as a string.