在SprintTodo中添加一个status列可能会更简单，但是有一种方法：

class SprintTodo < ApplicationRecord
  belongs_to :todo
  belongs_to :sprint

  acts_as_list scope: "sprint_todos.id IN (\#{todo_status_sql}) AND sprint_todos.sprint_id = \#{sprint_id}"

  def todo_status_sql
    SprintTodo.select(:id).joins(:todo).where(todo: { status: todo.status }).to_sql
  end
end

Sprint.create!
Todo.create!([{ status: :one }, { status: :one }, { status: :two }, { status: :two }])
Sprint.first.todos << Todo.all
Sprint.create!
Sprint.second.todo << Todo.create(status: :one)

>> SprintTodo.all.as_json(only: [:position, :sprint_id], include: {todo: {only: [:status, :id]}})
=> 
[{"position"=>1, "sprint_id"=>1, "todo"=>{"id"=>1, "status"=>"one"}},
 {"position"=>2, "sprint_id"=>1, "todo"=>{"id"=>2, "status"=>"one"}},

 {"position"=>1, "sprint_id"=>1, "todo"=>{"id"=>3, "status"=>"two"}},
 {"position"=>2, "sprint_id"=>1, "todo"=>{"id"=>4, "status"=>"two"}},

 {"position"=>1, "sprint_id"=>2, "todo"=>{"id"=>5, "status"=>"one"}}]
#             ^               ^                               ^
#     positioned        by sprint                 and todo.status

• 网址：http：//www.example.comwww.rubydoc.info/gems/acts_as_list/0.8.2/ActiveRecord/Acts/List/ClassMethods#acts_as_list-instance_method*