[[mapping-all-field]]
=== `_all`

The idea of the `_all` field is that it includes the text of one or more
other fields within the document indexed. It can come very handy
especially for search requests, where we want to execute a search query
against the content of a document, without knowing which fields to
search on. This comes at the expense of CPU cycles and index size.

The `_all` fields can be completely disabled. Explicit field mappings and
object mappings can be excluded / included in the `_all` field. By
default, it is enabled and all fields are included in it for ease of
use.

When disabling the `_all` field, it is a good practice to set
`index.query.default_field` to a different value (for example, if you
have a main "message" field in your data, set it to `message`).

One of the nice features of the `_all` field is that it takes into
account specific fields boost levels. Meaning that if a title field is
boosted more than content, the title (part) in the `_all` field will
mean more than the content (part) in the `_all` field.

Here is a sample mapping:

[source,js]
--------------------------------------------------
{
    "person" : {
        "_all" : {"enabled" : true},
        "properties" : {
            "name" : {
                "type" : "object",
                "dynamic" : false,
                "properties" : {
                    "first" : {"type" : "string", "store" : true , "include_in_all" : false},
                    "last" : {"type" : "string", "index" : "not_analyzed"}
                }
            },
            "address" : {
                "type" : "object",
                "include_in_all" : false,
                "properties" : {
                    "first" : {
                        "properties" : {
                            "location" : {"type" : "string", "store" : true}
                        }
                    },
                    "last" : {
                        "properties" : {
                            "location" : {"type" : "string"}
                        }
                    }
                }
            },
            "simple1" : {"type" : "long", "include_in_all" : true},
            "simple2" : {"type" : "long", "include_in_all" : false}
        }
    }
}
--------------------------------------------------

The `_all` fields allows for `store`, `term_vector` and `analyzer` (with
specific `analyzer` and `search_analyzer`) to be set.

[float]
[[highlighting]]
==== Highlighting

For any field to allow
<<search-request-highlighting,highlighting>> it has
to be either stored or part of the `_source` field. By default the `_all`
field does not qualify for either, so highlighting for it does not yield
any data.

Although it is possible to `store` the `_all` field, it is basically an
aggregation of all fields, which means more data will be stored, and
highlighting it might produce strange results.