[[search-validate]]
=== Validate API

The validate API allows a user to validate a potentially expensive query
without executing it. We'll use the following test data to explain _validate:

[source,console]
--------------------------------------------------
PUT twitter/_bulk?refresh
{"index":{"_id":1}}
{"user" : "kimchy", "post_date" : "2009-11-15T14:12:12", "message" : "trying out Elasticsearch"}
{"index":{"_id":2}}
{"user" : "kimchi", "post_date" : "2009-11-15T14:12:13", "message" : "My username is similar to @kimchy!"}
--------------------------------------------------
// TESTSETUP

When sent a valid query:

[source,console]
--------------------------------------------------
GET twitter/_validate/query?q=user:foo
--------------------------------------------------

The response contains `valid:true`:

[source,console-result]
--------------------------------------------------
{"valid":true,"_shards":{"total":1,"successful":1,"failed":0}}
--------------------------------------------------


[float]
=== Request Parameters

When executing exists using the query parameter `q`, the query passed is
a query string using Lucene query parser. There are additional
parameters that can be passed:

[cols="<,<",options="header",]
|=======================================================================
|Name |Description
|`df` |The default field to use when no field prefix is defined within the
query.

|`analyzer` |The analyzer name to be used when analyzing the query string.

|`default_operator` |The default operator to be used, can be `AND` or
`OR`. Defaults to `OR`.

|`lenient` |If set to true will cause format based failures (like
providing text to a numeric field) to be ignored. Defaults to false.

|`analyze_wildcard` |Should wildcard and prefix queries be analyzed or
not. Defaults to `false`.
|=======================================================================

The query may also be sent in the request body:

[source,console]
--------------------------------------------------
GET twitter/_validate/query
{
  "query" : {
    "bool" : {
      "must" : {
        "query_string" : {
          "query" : "*:*"
        }
      },
      "filter" : {
        "term" : { "user" : "kimchy" }
      }
    }
  }
}
--------------------------------------------------

NOTE: The query being sent in the body must be nested in a `query` key, same as
the <<search-search,search api>> works

If the query is invalid, `valid` will be `false`. Here the query is
invalid because Elasticsearch knows the post_date field should be a date
due to dynamic mapping, and 'foo' does not correctly parse into a date:

[source,console]
--------------------------------------------------
GET twitter/_validate/query
{
  "query": {
    "query_string": {
      "query": "post_date:foo",
      "lenient": false
    }
  }
}
--------------------------------------------------

[source,console-result]
--------------------------------------------------
{"valid":false,"_shards":{"total":1,"successful":1,"failed":0}}
--------------------------------------------------

An `explain` parameter can be specified to get more detailed information
about why a query failed:

[source,console]
--------------------------------------------------
GET twitter/_validate/query?explain=true
{
  "query": {
    "query_string": {
      "query": "post_date:foo",
      "lenient": false
    }
  }
}
--------------------------------------------------

responds with:

[source,console-result]
--------------------------------------------------
{
  "valid" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "failed" : 0
  },
  "explanations" : [ {
    "index" : "twitter",
    "valid" : false,
    "error" : "twitter/IAEc2nIXSSunQA_suI0MLw] QueryShardException[failed to create query:...failed to parse date field [foo]"
  } ]
}
--------------------------------------------------
// TESTRESPONSE[s/"error" : "[^\"]+"/"error": "$body.explanations.0.error"/]

When the query is valid, the explanation defaults to the string
representation of that query. With `rewrite` set to `true`, the explanation
is more detailed showing the actual Lucene query that will be executed.

For More Like This:

[source,console]
--------------------------------------------------
GET twitter/_validate/query?rewrite=true
{
  "query": {
    "more_like_this": {
      "like": {
        "_id": "2"
      },
      "boost_terms": 1
    }
  }
}
--------------------------------------------------
// TEST[skip:the output is randomized depending on which shard we hit]

Response:

[source,console-result]
--------------------------------------------------
{
   "valid": true,
   "_shards": {
      "total": 1,
      "successful": 1,
      "failed": 0
   },
   "explanations": [
      {
         "index": "twitter",
         "valid": true,
         "explanation": "((user:terminator^3.71334 plot:future^2.763601 plot:human^2.8415773 plot:sarah^3.4193945 plot:kyle^3.8244398 plot:cyborg^3.9177752 plot:connor^4.040236 plot:reese^4.7133346 ... )~6) -ConstantScore(_id:2)) #(ConstantScore(_type:_doc))^0.0"
      }
   ]
}
--------------------------------------------------

By default, the request is executed on a single shard only, which is randomly
selected. The detailed explanation of the query may depend on which shard is
being hit, and therefore may vary from one request to another. So, in case of
query rewrite the `all_shards` parameter should be used to get response from
all available shards.

For Fuzzy Queries:

[source,console]
--------------------------------------------------
GET twitter/_validate/query?rewrite=true&all_shards=true
{
  "query": {
    "match": {
      "user": {
        "query": "kimchy",
        "fuzziness": "auto"
      }
    }
  }
}
--------------------------------------------------

Response:

[source,console-result]
--------------------------------------------------
{
  "valid": true,
  "_shards": {
    "total": 1,
    "successful": 1,
    "failed": 0
  },
  "explanations": [
    {
      "index": "twitter",
      "shard": 0,
      "valid": true,
      "explanation": "(user:kimchi)^0.8333333 user:kimchy"
    }
  ]
}
--------------------------------------------------