Specify serialization for a field inside a Document

[anti-social]

At the moment Document describes Elasticsearch field types:

object UserDoc : Document() {
    // Elasticsearch doesn't have separate list type, almost all types are multi-valued
    val groups by keyword()
}

And concrete serialization is specified inside a document source:

class User : DocSource() {
    // Here `groups` value deserializes into a list of keywords
    val goups by UserDoc.groups.list()
}

Consider to specify serialization when describing a Document:

object UserDoc : Document() {
    // When generating a mapping it will be just a `keyword` type
    val groups by keyword().list()
}

class User : DocSource() {
    // Document source should take into account that it is a list of keywords
    val groups by UserDoc.groups
}

[anti-social]

Think it is not possible. The problem appears when dealing with sub-documents and sub-fields:

class NameSubFields<V>(field: BoundField<V>) : SubFields<V>(field) {
    val sort by keyword()
}

Now imagine these variants:

object ProductDoc : Document() {
    val name: NameSubFields<String?> by text().subFields(::NameSubFields)
}

object ProductDocV2 : Document() {
    // `::NameSubFields` has type of `(BoundField<String>) -> NameSubFields<String?>`
    val name: NameSubFields<String> by text().subFields(::NameSubFields)
        // What type should return `required`? We cannot transform `NameSubFields<String?>` into `NameSubFields<String>`
        .required()
}

[anti-social]

An example how it could be implemented: https://gist.github.com/anti-social/1a36d715ca8d8080c56a84bda0af2cc8

[anti-social]

Such a scheme has some drawbacks:

• we cannot generate document source from a mapping. Do we really need it?
• also there could be multiple document types with common mapping

[anti-social]

#45