Creating with a changeset fails with Oracle

Start by tracing the changeset create path and how the Oracle adapter handles Sequel's supports_returning? result. Compare the failing Oracle behavior with the working SQLite case and the documented create workaround; done means changesets can create records without requiring a returned INSERT result.

From @mrship on January 30, 2017 12:39

Using a changeset to create a record is failing for me when using Oracle, because (I think) you don't get the result of the INSERT statement back from Oracle using Sequel.

This is my code:

changeset_for_create = changeset(participant.to_hash)
  .map(:add_timestamps)
  .associate(participant.user, :users)
create(changeset_for_create(participant))

Which fails with:

2017-01-30 12:28:42 - Dry::Struct::Error - [ROM::Struct[Participant].new] :id is missing in Hash input:
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/dry-struct-0.1.1/lib/dry/struct/class_interface.rb:80:in `rescue in new'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/dry-struct-0.1.1/lib/dry/struct/class_interface.rb:74:in `new'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/class.rb:30:in `constructor_inject'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/function.rb:47:in `call'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/function.rb:47:in `call'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/array.rb:41:in `block in map_array'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/array.rb:41:in `map'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/array.rb:41:in `map_array'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/function.rb:47:in `call'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/transproc-1.0.0/lib/transproc/function.rb:47:in `call'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/rom-mapper-0.5.0/lib/rom/mapper.rb:95:in `block in call'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/rom-mapper-0.5.0/lib/rom/mapper.rb:95:in `each'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/rom-mapper-0.5.0/lib/rom/mapper.rb:95:in `reduce'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/rom-mapper-0.5.0/lib/rom/mapper.rb:95:in `call'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/rom-repository-1.0.0.rc1/lib/rom/repository.rb:326:in `map_tuple'
	/Users/shipmana/.rbenv/versions/2.2.5/lib/ruby/gems/2.2.0/gems/rom-repository-1.0.0.rc1/lib/rom/repository/class_interface.rb:117:in `block in define_command_method'

This works fine with sqlite (in a test) but not with our production database of Oracle. I have had a similar issue in the past when expecting create to return a ROM::Struct but it does not with Oracle because of the issue with Sequel not using RETURNING as part of the INSERT query. As I understand it Sequel returns false for supports_returning? for Oracle.

My workaround is not to use changesets at all...

attributes = participant.to_hash.merge(user_id: participant.user.id)
create(attributes)

which is a real shame as I like the interface they provide and the convenience of the associate method and adding timestamps etc.

Can changesets be made to work without expecting a result from the underlying INSERT?

Copied from original issue: rom-rb/rom-repository#55