How to return boolean result in named_scope?

named_scope :incomplete?, lambda { |user_id, todo_id| 
  { :select => 1, :conditions =>
    [ "#{user_id} not in (select user_todos.user_id from user_todos) and
       #{todo_id} not in (select user_todos.todo_id from user_todos)" ]
  } 
}

I'm getting a nil result. I开发者_JS百科 want it to return true. What I gotta do!?

Also, is there a better way to write this?

There's a huge issue with your code: named scopes are not intended to return booleans or single values, are intended to returns filters to be chained.

Use a class method instead. Also, use interpolation, don't write values directly into the SQL code.

class YourModel
  def self.incomplete?(user_id, todo_id)
    exists?(["? not in (select user_todos.user_id from user_todos) and ? not in (select user_todos.todo_id from user_todos)", user_id, todo_id])
  end
end

Thx. I discovered the issues! I ended up writing this:

def incomplete?(user_id, todo_id) return UserTodo.find_by_sql("select case when (#{user_id} not in (select user_id from user_todos)) and (#{todo_id} not in (select todo_id from user_todos)) then true else false end as incomplete from user_todos") end

But I like your approach better.