named scope vs. find_by_sql (specific example) - ruby-on-rails

Question

Just out of curiosity, does anyone know a better way of building the following collection using named scopes (as opposed to find_by_sql)?
#available = Workflow.find_by_sql(["
SELECT workflows.id FROM workflows
WHERE workflows.project_id = ? AND workflows.status < 5 AND
( workflows.created_by = ? OR workflows.id IN
(
SELECT workflow_id FROM workflow_histories
INNER JOIN workflow_recipients on workflow_histories.id = workflow_recipients.workflow_history_id
WHERE workflow_recipients.recipient_id = ? AND workflow_recipients.recipient_type = ?
)
)", project.id, #current_user.id, #current_user.id , 'USER'])

Answer 1

I haven't tested this, but I think it would work:
named_scope :available, lambda { |user_id, project_id|
{ :select => :id,
:conditions => [ "project_id = :project_id AND status < 5 AND
(created_by = :user_id OR id IN (
SELECT workflow_id FROM workflow_histories
INNER JOIN workflow_recipients ON workflow_histories.id = workflow_recipients.workflow_history_id
WHERE workflow_recipients.recipient_id = :user_id AND workflow_recipients.recipient_type = :recipient_type
)",
{ :user_id => user_id,
:project_id => project_id,
:recipient_type => "USER"
}
]
}
}
(A previous version of my answer breaks the sub-select out into its own query, which I think is unnecessary.)