elasticsearch/docs/reference/mapping/fields/parent-field.asciidoc

[[mapping-parent-field]]
=== `_parent`

The parent field mapping is defined on a child mapping, and points to
the parent type this child relates to. For example, in case of a `blog`
type and a `blog_tag` type child document, the mapping for `blog_tag`
should be:

[source,js]
--------------------------------------------------
{
    "blog_tag" : {
        "_parent" : {
            "type" : "blog"
        }
    }
}
--------------------------------------------------

The mapping is automatically stored and indexed (meaning it can be
searched on using the `_parent` field notation).

==== Field data loading

Contrary to other fields the fielddata loading is not `lazy`, but `eager`. The reason for this is that when this
field has been enabled it is going to be used in parent/child queries, which heavily relies on field data to perform
efficiently. This can already be observed during indexing after refresh either automatically or manually has been executed.