Left outer joining 2 fields referring to same User model in Rails 3 (Part 2)

arel_joins.rb

t = Task.arel_table
u = User.arel_table
c = u.alias("creators_tasks")

keyword = "%#{params}%"

relation = includes(:user_assigned,:creator)
.where(
 t[:id].matches(keyword)
 .or(u[:username].matches(keyword))
 .or(c[:username].matches(keyword))
)

# Outputs
# SELECT * FROM tasks LEFT OUTER JOIN users ON users.id = tasks.user_assigned_id AND users.deleted_at IS NULL LEFT OUTER 
# JOIN users creators_tasks ON creators_tasks.id = tasks.creator_id AND creators_tasks.deleted_at IS NULL WHERE 
# users.username LIKE 'Manager%'