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:
{
"blog_tag" : {
"_parent" : {
"type" : "blog"
}
}
}
The mapping is automatically stored and indexed (meaning it can be searched on using the _parent field notation).
