鑄造錯誤變更

我有我在與同時使用的變更問題，以下型號（聊天室）：鑄造錯誤變更

defmodule Elemental.TxChat.Room do 
    use Elemental.TxChat.Web, :model 

    schema "rooms" do 
    field :name, :string 

    # Foreign key indicating which user created this room 
    # One user can create any number of rooms 
    belongs_to :created_by, Elemental.TxChat.User 
    field :created_from_app, :integer 

    many_to_many :members, Elemental.TxChat.User, join_through: "rooms_users" 

    timestamps() 
    end 

    def changeset(struct, params \\ %{}) do 
    struct 
    |> cast(params, [:name, :created_by, :created_from_app]) 
    |> validate_required([:name, :created_by, :created_from_app]) 
    end 
end

轉念一想，我想嘗試傳遞一個空的結構到變更集並查看它產生的錯誤。所以，我沒有（後混疊）：

iex(4)> c = Room.changeset(%Room{}, %{}) 
** (RuntimeError) casting assocs with cast/3 is not supported, use cast_assoc/3 instead 
     (ecto) lib/ecto/changeset.ex:440: Ecto.Changeset.type!/2 
     (ecto) lib/ecto/changeset.ex:415: Ecto.Changeset.process_param/8 
    (elixir) lib/enum.ex:1151: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3 
    (elixir) lib/enum.ex:1151: Enum."-map_reduce/3-lists^mapfoldl/2-0-"/3 
     (ecto) lib/ecto/changeset.ex:391: Ecto.Changeset.do_cast/7 
    (tx_chat) web/models/room.ex:19: Elemental.TxChat.Room.changeset/2

我當時以爲型號有belongs_to等，具有cast_assoc工作，所以我改變了函數名。現在：

iex(4)> c = Room.changeset(%Room{}, %{}) 
** (FunctionClauseError) no function clause matching in Ecto.Changeset.cast_assoc/3 
     (ecto) lib/ecto/changeset.ex:518: Ecto.Changeset.cast_assoc(%Elemental.TxChat.Room{__meta__: #Ecto.Schema.Metadata<:built, "rooms">, created_by: #Ecto.Association.NotLoaded<association :created_by is not loaded>, created_by_id: nil, created_from_app: nil, id: nil, inserted_at: nil, members: #Ecto.Association.NotLoaded<association :members is not loaded>, name: nil, updated_at: nil}, %{}, [:name, :created_by, :created_from_app]) 
    (tx_chat) web/models/room.ex:19: Elemental.TxChat.Room.changeset/2

我在做什麼錯？

來源

2016-09-15 dotslash

你只需要改變'cast'到'cast_assoc'？嘗試'|> cast（params，[：name，：created_from_app]）|> cast_assoc（：created_by）'。 – Dogbert

讓我知道如果這工作，我會發表解釋的答案。 – Dogbert

@Dogbert所以這就是神祕之處！我真的很笨，只是用'cast_assoc'替換'cast'。非常感謝你每次幫助我。。。真的很感激它。請發表回答並解釋。 – dotslash

正如評論中所闡明的那樣，您希望將現有用戶與新房間相關聯。您可以通過在傳遞到cast,assoc_constraint(:created_by)的字段列表中添加created_by_id，然後將密鑰created_by_id中的用戶ID發送到Room.changeset/2來完成此操作。這應該工作：

def changeset(struct, params \\ %{}) do 
    struct 
    |> cast(params, [:name, :created_by_id, :created_from_app]) 
    |> validate_required([:name, :created_by_id, :created_from_app]) 
    |> assoc_constraint(:created_by) 
end

然後創建一個房間：

Room.changeset(%Room{}, %{name: "foo", created_by_id: 1, created_from_app: 1}) 
|> Repo.insert

來源

2016-09-16 06:23:24 Dogbert

鑄造錯誤變更

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