Fix columns error when using join queries

[addbrick]

When using the ActiveRecordEnumerator, Update validation of columns in active record enumerator to allow for Arel and String values.

This fixes a an issue where using join queries kept running into the columns error and passing in columns with . values would cause errors when the query was executed.

Example

# This would produce an error due to no "fully-qualified" columns
enumerator_builder.active_record_on_records(
  User.join(:memberships).where(memberships: { role: 'host' }),
  cursor: cursor,
  batch_size: 1
)

# If you add a columns field with symbols, you get the no fully-qualified columns error again
enumerator_builder.active_record_on_records(
  User.join(:memberships).where(memberships: { role: 'host' }),
  cursor: cursor,
  batch_size: 1,
  columns: [:id]
)

# If you attempted to add a string value with a fully-qualified column, you get a sql error when executing the query
enumerator_builder.active_record_on_records(
  User.join(:memberships).where(memberships: { role: 'host' }),
  cursor: cursor,
  batch_size: 1
  cursor: ['users.id']
)
# Produces a double table name in the sql query
`ORDER BY "users"."users.id"`

The change this PR is to only raise the error if the columns are not all Arel::Attributes::Attribute or string with no . in it. When you call to_s on a Arel::Attributes::Attribute it becomes fully qualified.

I believe this condition just missed getting updated with the move to convert all columns to Arel attributes for the ActiveRecordEnumerator, in this PR #456 from earlier this year.

[Mangara]

Thanks for fixing this! Could you add a test for this case?

We also need you to sign the CLA before we can merge it.

[addbrick]

Just an update, we ended up not needing this right away so it has become a lower priority. It is on my list to add tests and get this pr merged.