database - Elixir/Ecto 无法识别模型中的外键

Question

我收到以下错误 -

[error] GenServer #PID<0.398.0> terminating
** (Ecto.QueryError) deps/ecto/lib/ecto/association.ex:516: field `articles_id` in `where` does not exist in schema Newsly.Comments in query:

from c in Newsly.Comments,
  where: c.articles_id == ^1,
  order_by: [asc: c.articles_id],
  select: {c.articles_id, c}

    (elixir) lib/enum.ex:1826: Enum."-reduce/3-lists^foldl/2-0-"/3
    (elixir) lib/enum.ex:1372: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3
    (elixir) lib/enum.ex:1826: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ecto) lib/ecto/repo/queryable.ex:124: Ecto.Repo.Queryable.execute/5
    (ecto) lib/ecto/repo/queryable.ex:37: Ecto.Repo.Queryable.all/4
    (elixir) lib/enum.ex:1270: Enum."-map/2-lists^map/1-0-"/2
Last message: %Phoenix.Socket.Message{event: "addComment", join_ref: "43", payload: %{"articleid" => 1, "message" => "asdfasdfsasdfasdferqweasdfas", "user" => "peter"}, ref: "45", topic: "room:lobby"}
State: %Phoenix.Socket{assigns: %{}, channel: Newsly.RoomChannel, channel_pid: #PID<0.398.0>, endpoint: Newsly.Endpoint, handler: Newsly.UserSocket, id: nil, join_ref: "43", joined: true, private: %{log_handle_in: :debug, log_join: :info}, pubsub_server: Newsly.PubSub, ref: nil, serializer: Phoenix.Transports.V2.WebSocketSerializer, topic: "room:lobby", transport: Phoenix.Transports.WebSocket, transport_name: :websocket, transport_pid: #PID<0.389.0>, vsn: "2.0.0"}

这个错误的奇怪之处在于它说它找不到 articles_id，但我在预加载评论时调用了 article_id，并且在我的其余代码中调用了 article_id。

这里是我调用 Repo 的地方

defmodule Newsly.CommentController do
  alias Newsly.{Repo, Articles, Comments}

  def addComment(articleid, message, user) do
    IO.puts "inside addComment() in CommentController"

    article = Repo.get(Articles, articleid)
    |> Repo.preload(:comments) #this line is giving the error - when I take it out the error goes away (although comments are not preloaded)


    IO.puts "article"
    IO.inspect article

  end
end

这是我的模型 -

defmodule Newsly.Comments do
  use Newsly.Web, :model

  schema "comment" do
    field :body, :string
    field :user, :string
    field :upvotes, :integer
    field :downvotes, :integer
    field :flaggedcount, :integer
    belongs_to :article, Newsly.Articles, foreign_key: :article_id #I don't call articles_id here!!! only article_id (singular). Ecto is seeing in the database a relationship that does not exist!

    timestamps()
  end

  @doc """
  Builds a changeset based on the `struct` and `params`.
  """
  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [:body, :user, :upvotes, :downvotes, :flaggedcount])
    |> validate_required([:body, :user, :upvotes, :downvotes, :flaggedcount])
  end
end

只是为了仔细检查....

这是我在本地的 postgres 数据库关联 - 注意 article_id 存在(不是 articles_id)

newsly_dev=# table comment;
 id | body | user | upvotes | downvotes | flaggedcount | article_id | inserted_at | updated_at 
----+------+------+---------+-----------+--------------+------------+-------------+------------
(0 rows)

我完全迷路了。有人有什么想法吗？

Answer 1

由于您首先获取一篇文章，然后获取其评论，Ecto 将使用 Articles 模型的 has_many 声明，您很可能会错过自定义 foreign_key 在里面。

has_many :comments, Newsly.Comments, foreign_key: :article_id
                                     ^^^^^^^^^^^^^^^^^^^^^^^^