Ecto:如何从外键中的某个字段订购结果

Question

所以我有一个属于用户的模型Ticket.每个用户都有很多票.因此user_id是每个Ticket的外键.如何构建一个查询,以获取每个用户的用户名所订购的所有票证？我一直在努力

    query       = from u in User, 
                                        preload: [:tickets]

    query_tickets = from t in Ticket,
                                        order_by: u.username,
                                        preload: [users: ^query]

    tickets = Repo.all(query_tickets)

但它说模型Ticket没有任何用户关联？

     schema "tickets" do
    field :subject,           :string
    field :body,              :string
    field :followup,          :boolean
    field :closed,            :boolean
    field :file,              :string
    field :filepath,          :map
    belongs_to :user,         UserController
    has_many :ticket_message, TicketMessageController


    timestamps
  end

    schema "users" do 
    field :name,                    :string
    field :username,            :string
    field :password,            :string, virtual: true
    field :password_hash, :string
    field :email,               :string
    field :client,              :string
    field :role,                    :integer
    has_one :services, ServiceController
    has_many :tickets, TicketController

    timestamps
end

Answer 1

你在这里使用preload/3,因为preload发生在查询之后(它将在它自己的查询中获取所有相关的id)你不能以这种方式对user_id进行排序.

来自文档:

Repo.all from p in Post, preload: [:comments]

上面的示例将从数据库中获取所有帖子,然后执行单独的查询,返回与给定帖子关联的所有评论.

你必须使用join/5

query_tickets = from t in Ticket,
  join: u in assoc(t, :user)
  order_by: u.username,

tickets = Repo.all(query_tickets)

如果您希望将用户设置在user故障单的密钥上(就像您预先加载一样),那么您可能需要查看https://github.com/elixir-lang/ecto/issues/962