Request to make `self.partial_writes` configurable per database adapter

gistfile1.txt

* Summary

Make `self.partial_writes` configurable per database adapter, not per model
or always write primary key attribute name per database adapter in the next major version of Rails 6.

* Background for this idea

Identity data type support for Oracle database 12.2 or higher.
It is a kind of standard auto_increment support for Oracle database.

Oracle database had not support auto increment type primary key, 
then Oracle ehnanced adapter `prefetch_primary_key` returns `true` 
then the adapter needs to select primary key value from the associated sequence.

Once supporting identity data type, `prefetch_primary_key` value can be `false`.
but there is a problem. Once we do not have to prefetch primary key, 
Many sql statements will not specify any column names then `empty_insert_statement_value` method executed
it raises `NotImplementedError` finally.

Because unfortunately, Oracle database does not support `insert into default values` statement then
`empty_insert_statement_value` method raises `NotImplementedError`.
Still there is no plan that Oracle database support `INSERT .. DEFAULT VALUES`.

Ryuta Kamizono aka @kamipo suggested setting `self.partial_writes` can workaround this problem.
And actually it does. partial_writes belongs to each Active Record model. 

I'd like that the next major version of Rails can make `self.partial_writes` default configuable
per database adapter or always write primary key attribute name per database adapter.


* Reference

[Identity Columns in Oracle Database 12c Release 1 (12.1)](https://oracle-base.com/articles/12c/identity-columns-in-oracle-12cr1)

[Raise NotImplementedError when using empty_insert_statement_value with Oracle](https://github.com/rails/rails/pull/28029)

[Add support for INSERT .. DEFAULT VALUES](https://community.oracle.com/ideas/13845)
 

Here is the repository for Oracle identity type script files https://github.com/yahonda/sample_app_for_oracle_identity