Allow index settings in Meta.index

Currently, when defining a new DocType you have to create a separate Index object if you wish to configure any index-level settings. With the deprecation of multiple types in elasticsearch 6.0 it might make more sense to just allow the index settings to configurable on the DocType itself in some fashion.

This would then allow even for situations where given DocType is present in multiple indices (time-based indices for example) meaning its Meta.index would specify a wildcard (products-* for example) and provide settings which would then allow it to generate and save an IndeTemplate and/or create any particular index via the init classmethod.

Any ideas and feedback is more than welcome!

Inspired by @3lnc’s comment: https://github.com/elastic/elasticsearch-dsl-py/issues/779#issuecomment-350047587

[honzakral]

I absolutely agree that Index/DocType distinction is no longer useful. What if we changed things around a bit, just brainstorming here so not all might make it to the target design or even make sense:

• rename DocType to Document
• remove all index-related options from Meta and ._doc_type
  • including init and index name
• add class Index: as an (optional) section to Document that can contain definitions for:
  • index name (can contain a wildcard)
  • index settings/analyzers
  • method do determine index name for a document (like looking at a timestamp for example to go from my-idx-* to my-idx-2018.01.01)
  • template_name if this definition if to be defined via a template
  • rollover settings
  • alias setting allowing for some rules to
• use those definitions to construct an Index object that will be accessible on the Document class (.index ??) which will:
  • store all the settings provided in the Index class
  • provide mechanisms for index management - create/create_template/delete/switch_alias (by default point an alias to latest index in the group)/rollover/shrink/allocation/…
  • have helper methods like migrate which will create a new index, reindex data from another index and swap alias

If someone wants to have multiple Document classes stored in a single index, the recommended way would be to use inheritance and override Meta.matches to dynamically determine which class to use for every hit returned. Question is how to then make sure the mappings get merged - I like the idea of a Document class iterating through all its subclasses and collecting mappings but it might be too confusing and dangerous so maybe we just do it explicitly somehow?

What do you think?

[honzakral]

#840 is ready for review and contains some examples showcasing some of the techniques made possible by this change