Avoid Early DB Connection when Using index_scope w/ ActiveRecord Relation

[jpterry]

Is your feature request related to a problem? Please describe.

When using Index.index_scope we would like to pass an ActiveRecord Relation, using ActiveRecord::Query#includes, like so:

class MyIndex < Chewy::Index
  index_scope MyRecord.includes(:company, :owner, :parent, :children)
  ...

In our environments that eager load classes, like production, we find that this causes some very early database connections.

This also has the consequence of causing our rails app to fail to boot if the database is down. We would like to avoid this coupling in our application.

The stack trace where this is happening:

from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/activerecord-7.0.8.4/lib/active_record/connection_handling.rb:313:in `retrieve_connection'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/activerecord-7.0.8.4/lib/active_record/connection_handling.rb:280:in `connection'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/activerecord-7.0.8.4/lib/active_record/relation/delegation.rb:93:in `connection'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/activerecord-7.0.8.4/lib/active_record/relation/query_methods.rb:1625:in `preprocess_order_args'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/activerecord-7.0.8.4/lib/active_record/relation/query_methods.rb:498:in `reorder!'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/activerecord-7.0.8.4/lib/active_record/relation/query_methods.rb:493:in `reorder'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/chewy-8.0.0.pre.beta/lib/chewy/index/adapter/active_record.rb:31:in `cleanup_default_scope!'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/chewy-8.0.0.pre.beta/lib/chewy/index/adapter/orm.rb:18:in `initialize'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/chewy-8.0.0.pre.beta/lib/chewy/index.rb:167:in `new'
from /Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/gems/3.3.0/gems/chewy-8.0.0.pre.beta/lib/chewy/index.rb:167:in `index_scope'
from /Users/john/Code/my_api/app/elastic_indexing/my_index.rb:4:in `<class:MyIndex>'
from /Users/john/Code/my_api/app/elastic_indexing/my_index.rb:1:in `<top (required)>'
from <internal:/Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/3.3.0/rubygems/core_ext/kernel_require.rb>:37:in `require'
from <internal:/Users/john/.asdf/installs/ruby/3.3.5/lib/ruby/3.3.0/rubygems/core_ext/kernel_require.rb>:37:in `require'

Note that it's Chewy's cleanup_default_scope! call to reorder that triggers the establishment of a connection.

Describe the solution you'd like

I would like to be able to avoid establishing a connection when using this pattern, until the db connection is needed.

OR

I would like to be able to call index_scope passing a lambda or proc, while also telling index_scope to use the ActiveRecord adapter.

Describe alternatives you've considered

• Based on Make default index scope cleanup behavior configurable #925 I had hoped that setting
  Chewy.import_scope_cleanup_behavior = :ignore would avoid this, however it looks like reorder is called regardless of this being set.

• It also technically "works" to pass a lambda or proc to index_scope, but this method isn't able to leverage the activerecord adapter properly.

Additional context

We're currently using 8.0.0.pre.beta, but all the same code is present in master.