Elixir Ecto：如何存储关于多对多关系的元信息

Question

假设我有模型 User 和 Organization 以及两者之间的多对多关系。我现在想添加有关两者之间关系的信息。例如 timestamps 和 position。我该如何处理以及如何查询此信息？

我认为正确的方向是使用连接模式。按照 Ecto 文档，类似于：

defmodule UserOrganization do
  use Ecto.Schema

  @primary_key false
  schema "users_organizations" do
    field :position, :string # adding information on the position of the user within the organization
    belongs_to :user, User
    belongs_to :organization, Organization
    timestamps # Added bonus, a join schema will also allow you to set timestamps
  end

  def changeset(struct, params \ %{}) do
    struct
    |> Ecto.Changeset.cast(params, [:user_id, :organization_id])
    |> Ecto.Changeset.validate_required([:user_id, :organization_id])
    # Maybe do some counter caching here!
  end
end

defmodule User do
  use Ecto.Schema

  schema "users" do
    many_to_many :organizations, Organization, join_through: UserOrganization
  end
end

defmodule Organization do
  use Ecto.Schema

  schema "organizations" do
    many_to_many :users, User, join_through: UserOrganization
  end
end

# Then to create the association, pass in the ID's of an existing
# User and Organization to UserOrganization.changeset
changeset = UserOrganization.changeset(%UserOrganization{}, %{user_id: id, organization_id: id})

case Repo.insert(changeset) do
  {:ok, assoc} -> # Assoc was created!
  {:error, changeset} -> # Handle the error
end

现在如何在创建记录时设置 position 以及如何查询 timestamps 和 position？

Answer 1

如果您想检索复合模式的 timestamps 和 position，您可以在 User 和 Organization 上添加 has_many 关系, 像这样

defmodule Organization do
  use Ecto.Schema

  schema "organizations" do
    many_to_many :users, User, join_through: UserOrganization
    has_many :user_organizations, UserOrganization
  end
end

然后您可以在检索 Organization 时 Repo.preload 关系 user_organizations，您将可以使用 UserOrganization 的所有属性。

关于如何设置 position 你可以将它添加到变更集中并确保你在 UserOrganization 模式

上允许参数

 def changeset(struct, params \ %{}) do
    struct
    |> Ecto.Changeset.cast(params, [:user_id, :organization_id, :position])
    |> Ecto.Changeset.validate_required([:user_id, :organization_id])
    # Maybe do some counter caching here!
  end

changeset = UserOrganization.changeset(%UserOrganization{}, %{user_id: id, organization_id: id, position: position})

它应该对你很好。

Elixir Ecto：如何存储关于多对多关系的元信息

Elixir Ecto: How to store meta information about a many-to-many relationship

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