[Rails]: Generate Complex OR Query on Rails 3 with Arel

On the Rails 3, ActiveRecord generate QSL through DSL "Arel". There are many simple query sample codes are available, but complex one is a little. This post shows how to generate complex "OR" query. I want to write such a code below (like Propel for PHP):

 
def foo
  # generate condition A
  # generate condition B
  some_array.each do |h|
    # generate condition A to N
  end
  # return condition which is concatenated by "OR" clause.
end

One simple idea, I wrote (like Doctrine for PHP):

 
Foo.where(CONDITION1).or(CONDITION2).or(CONDITION3)

But it does not work. A correct answer is below (use "scoped"):

 
conds = Array.new
f = Foo.scoped
 
conds << f.tables[:field_name].eq('FOO')
some_array.each do |c|
  conds << f.tables[:field_name].SOME_METHOD()
end
cond = nil
conds.each do |c|
  if not cond
    cond = c
  else
    cond = cond.or(c)
  end
end
return Foo.where(cond)

The code generates "(((COND1 OR COND2) OR COND3) OR COND4)" where clause.