Id Field Mapping - gnuhub/elasticsearch GitHub Wiki

Each document indexed is associated with an id and a type. The id, when indexing, is automatically indexed into an _id field. By default, the _id field is indexed (but not analyzed) and not stored. This means that the _id field can be used to query against it.

The _id field allows to store it as well, for example:

{
    "tweet" : {
        "_id" : {"store" : "yes"}
    }
}