[[search-template]]
== Search Template

The `/_search/template` endpoint allows to use the mustache language to pre render search requests,
before they are executed and fill existing templates with template parameters.

[source,js]
------------------------------------------
GET /_search/template
{
    "inline" : {
      "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].

NOTE: The mustache language is implemented in elasticsearch as a sandboxed
scripting language, hence it obeys settings that may be used to enable or
disable scripts per language, source and operation as described in
<<enable-dynamic-scripting, scripting docs>>

[float]
==== More template examples

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

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

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

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

which is rendered as:

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


[float]
===== Concatenating array of values

The `{{#join}}array{{/join}}` function can be used to concatenate the
values of an array as a comma delimited string:

[source,js]
------------------------------------------
GET /_search/template
{
  "inline": {
    "query": {
      "match": {
        "emails": "{{#join}}emails{{/join}}"
      }
    }
  },
  "params": {
    "emails": [ "username@email.com", "lastname@email.com" ]
  }
}
------------------------------------------

which is rendered as:

[source,js]
------------------------------------------
{
    "query" : {
        "match" : {
            "emails" : "username@email.com,lastname@email.com"
        }
    }
}
------------------------------------------

The function also accepts a custom delimiter:

[source,js]
------------------------------------------
GET /_search/template
{
  "inline": {
    "query": {
      "range": {
        "born": {
            "gte"   : "{{date.min}}",
            "lte"   : "{{date.max}}",
            "format": "{{#join delimiter='||'}}date.formats{{/join delimiter='||'}}"
	    }
      }
    }
  },
  "params": {
    "date": {
        "min": "2016",
        "max": "31/12/2017",
        "formats": ["dd/MM/yyyy", "yyyy"]
    }
  }
}
------------------------------------------

which is rendered as:

[source,js]
------------------------------------------
{
    "query" : {
      "range" : {
        "born" : {
          "gte" : "2016",
          "lte" : "31/12/2017",
          "format" : "dd/MM/yyyy||yyyy"
        }
      }
    }
}

------------------------------------------


[float]
===== Default values

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

[source,js]
------------------------------------------
{
  "inline": {
    "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]
===== Converting parameters to JSON

The `{{toJson}}parameter{{/toJson}}` function can be used to convert parameters
like maps and array to their JSON representation:

[source,js]
------------------------------------------
{
    "inline": "{\"query\":{\"bool\":{\"must\": {{#toJson}}clauses{{/toJson}} }}}",
    "params": {
        "clauses": [
            { "term": "foo" },
            { "term": "bar" }
        ]
   }
}
------------------------------------------

which is rendered as:

[source,js]
------------------------------------------
{
    "query" : {
      "bool" : {
        "must" : [
          {
            "term" : "foo"
          },
          {
            "term" : "bar"
          }
        ]
      }
    }
}
------------------------------------------


[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]
------------------------------------------
{
  "query": {
    "bool": {
      "must": {
        "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`

[NOTE]
==================================
As written above, this template is not valid JSON because it includes the
_section_ markers like `{{#line_no}}`.  For this reason, the template should
either be stored in a file (see <<pre-registered-templates>>) or, when used 
via the REST API, should be written as a string:

[source,js]
--------------------
"inline": "{\"query\":{\"bool\":{\"must\":{\"match\":{\"line\":\"{{text}}\"}},\"filter\":{{{#line_no}}\"range\":{\"line_no\":{{{#start}}\"gte\":\"{{start}}\"{{#end}},{{/end}}{{/start}}{{#end}}\"lte\":\"{{end}}\"{{/end}}}}{{/line_no}}}}}}"
--------------------

==================================

[float]
[[pre-registered-templates]]
===== Pre-registered template

You can register search templates by storing it in the `config/scripts` directory, in a file using the `.mustache` extension.
In order to execute the stored template, reference it by it's name under the `template` key:


[source,js]
------------------------------------------
GET /_search/template
{
    "file": "storedTemplate", <1>
    "params": {
        "query_string": "search for these words"
    }
}
------------------------------------------

<1> Name of the query template in `config/scripts/`, i.e., `storedTemplate.mustache`.

You can also register search templates by storing it in the cluster state.
There are REST APIs to manage these indexed templates.

[source,js]
------------------------------------------
POST /_search/template/<templatename>
{
    "template": {
        "query": {
            "match": {
                "title": "{{query_string}}"
            }
        }
    }
}
------------------------------------------

This template can be retrieved by

[source,js]
------------------------------------------
GET /_search/template/<templatename>
------------------------------------------

which is rendered as:

[source,js]
------------------------------------------
{
    "template": {
        "query": {
            "match": {
                "title": "{{query_string}}"
            }
        }
    }
}
------------------------------------------

This template can be deleted by

[source,js]
------------------------------------------
DELETE /_search/template/<templatename>
------------------------------------------

To use an indexed template at search time use:


[source,js]
------------------------------------------
GET /_search/template
{
    "id": "templateName", <1>
    "params": {
        "query_string": "search for these words"
    }
}
------------------------------------------
<1> Name of the query template stored in the `.scripts` index.

[float]
==== Validating templates

A template can be rendered in a response with given parameters using

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

This call will return the rendered template:

[source,js]
------------------------------------------
{
  "template_output": {
    "query": {
      "terms": {
        "status": [ <1>
          "pending",
          "published"
        ]
      }
    }
  }
}
------------------------------------------
<1> `status` array has been populated with values from the `params` object.

File and indexed templates can also be rendered by replacing `inline` with 
`file` or `id` respectively. For example, to render a file template

[source,js]
------------------------------------------
GET /_render/template
{
  "file": "my_template",
  "params": {
    "status": [ "pending", "published" ]
  }
}
------------------------------------------

Pre-registered templates can also be rendered using

[source,js]
------------------------------------------
GET /_render/template/<template_name>
{
  "params": {
    "..."
  }
}
------------------------------------------

[[multi-search-template]]
== Multi Search Template

The multi search template API allows to execute several search template
requests within the same API using the `_msearch/template` endpoint.

The format of the request is similar to the <<search-multi-search, Multi
Search API>> format:

[source,js]
--------------------------------------------------
header\n
body\n
header\n
body\n
--------------------------------------------------

The header part supports the same `index`, `types`, `search_type`,
`preference`, and `routing` options as the usual Multi Search API.

The body includes a search template body request and supports inline,
stored and file templates. Here is an example:

[source,js]
--------------------------------------------------
$ cat requests
{"index": "test"}
{"inline": {"query": {"match":  {"user" : "{{username}}" }}}, "params": {"username": "john"}} <1>
{"index": "_all", "types": "accounts"}
{"inline": {"query": {"{{query_type}}": {"name": "{{name}}" }}}, "params": {"query_type": "match_phrase_prefix", "name": "Smith"}}
{"index": "_all"}
{"id": "template_1", "params": {"query_string": "search for these words" }} <2>
{"types": "users"}
{"file": "template_2", "params": {"field_name": "fullname", "field_value": "john smith" }} <3>

$ curl -XGET localhost:9200/_msearch/template --data-binary "@requests"; echo
--------------------------------------------------
<1> Inline search template request

<2> Search template request based on a stored template

<3> Search template request based on a file template

The response returns a `responses` array, which includes the search template
response for each search template request matching its order in the original
multi search template request. If there was a complete failure for that specific
search template request, an object with `error` message will be returned in place
of the actual search response.