[[query-dsl-terms-query]]
== Terms Query

Filters documents that have fields that match any of the provided terms
(*not analyzed*). For example:

[source,js]
--------------------------------------------------
{
    "constant_score" : {
        "filter" : {
            "terms" : { "user" : ["kimchy", "elasticsearch"]}
        }
    }
}
--------------------------------------------------

The `terms` query is also aliased with `in` as the filter name for
simpler usage.

[float]
==== Terms lookup mechanism

When it's needed to specify a `terms` filter with a lot of terms it can
be beneficial to fetch those term values from a document in an index. A
concrete example would be to filter tweets tweeted by your followers.
Potentially the amount of user ids specified in the terms filter can be
a lot. In this scenario it makes sense to use the terms filter's terms
lookup mechanism.

The terms lookup mechanism supports the following options:

[horizontal]
`index`:: 
    The index to fetch the term values from. Defaults to the
    current index.

`type`:: 
    The type to fetch the term values from.

`id`:: 
    The id of the document to fetch the term values from.

`path`:: 
    The field specified as path to fetch the actual values for the
    `terms` filter.

`routing`:: 
    A custom routing value to be used when retrieving the
    external terms doc.

The values for the `terms` filter will be fetched from a field in a
document with the specified id in the specified type and index.
Internally a get request is executed to fetch the values from the
specified path. At the moment for this feature to work the `_source`
needs to be stored.

Also, consider using an index with a single shard and fully replicated
across all nodes if the "reference" terms data is not large. The lookup
terms filter will prefer to execute the get request on a local node if
possible, reducing the need for networking.

[float]
==== Terms lookup twitter example

[source,js]
--------------------------------------------------
# index the information for user with id 2, specifically, its followers
curl -XPUT localhost:9200/users/user/2 -d '{
   "followers" : ["1", "3"]
}'

# index a tweet, from user with id 2
curl -XPUT localhost:9200/tweets/tweet/1 -d '{
   "user" : "2"
}'

# search on all the tweets that match the followers of user 2
curl -XGET localhost:9200/tweets/_search -d '{
  "query" : {
    "filtered" : {
      "filter" : {
        "terms" : {
          "user" : {
            "index" : "users",
            "type" : "user",
            "id" : "2",
            "path" : "followers"
          }
        }
      }
    }
  }
}'
--------------------------------------------------

The structure of the external terms document can also include array of
inner objects, for example:

[source,js]
--------------------------------------------------
curl -XPUT localhost:9200/users/user/2 -d '{
 "followers" : [
   {
     "id" : "1"
   },
   {
     "id" : "2"
   }
 ]
}'
--------------------------------------------------

In which case, the lookup path will be `followers.id`.