为多对多强制转换关联变更集

我在用户和设施之间有这么多对多的关系:

schema "facilities" do    
  field(:name, :string)
  field(:description, :string)    
  many_to_many(:users, User, join_through: "users_facilities")
end

schema "users" do
  field(:first_name, :string)
  field(:last_name, :string)
  field(:email_address, :string)
  field(:username, :string)
  many_to_many(:facilities, Facility, join_through: "users_facilities")
end

这就是 changeset_params :

  %{
  name: john,
  users: [%{id: 1286, name: "john doe"}, %{id: 1287, name: "jane doe"}]
 }

它对 has_many 给我一个完整的关联的变更集。但不适合 many to many .

这个 records_struct 将完整的设施关联加载到用户 这是代码:

    Facility.changeset(records_struct, changeset_params)
    |> Ecto.Changeset.cast_assoc(:users)

我从facility.changeset得到changeset返回,但是 Ecto.Changeset.cast_assoc 投掷 internal server 尝试测试时出错。