如何为 has_one / belongs_to_many 关联定义 Elixir Ecto 架构？

Question

在属于 To/Has 的一个协会的解释中，作者在 https://elixirschool.com/en/lessons/ecto/associations/#belongs-tohas-one 写道：

Let’s say that a movie has one distributor, for example Netflix is the distributor of their original film “Bright”.

...

...the Distributor schema should use the belongs_to/3 macro to allow us to call distributor.movie and look up a distributor’s associated movie using this foreign key.

...

The has_one/3 macro functions just like the has_many/3 macro. It uses the associated schema’s foreign key to look up and expose the movie’s distributor. This will allow us to call movie.distributor.

以下是他们示例的架构：

defmodule Example.Distributor do
  use Ecto.Schema

  schema "distributors" do
    field :name, :string
    belongs_to :movie, Example.Movie
  end
end

defmodule Example.Movie do
  use Ecto.Schema

  schema "movies" do
    field :title, :string
    field :tagline, :string
    has_many :characters, Example.Character
    has_one :distributor, Example.Distributor # I'm new!
  end
end

José Valim writes in http://blog.plataformatec.com.br/2015/08/working-with-ecto-associations-and-embeds/:

The difference between has_one/3 and belongs_to/3 is that the foreign key is always defined in the schema that invokes belongs_to/3.

因此，通过在分销商架构中使用 belongs_to/3，在该架构中定义了一个外键，将此示例中的单个分销商限制为单个电影。（示例作者的“...允许我们调用 distributor.movie 并使用此外键查找发行商的关联电影”证实了这一点。）

如果我希望一部电影有一个发行商，但一个发行商有一部 或更多 部电影，我将如何定义模式？

Answer 1

你反了。

如果一部电影只有一个发行商，则将外键放入其架构中。

然后，当您需要为某个特定发行商查找电影时，您只需查找具有引用发行商 ID 的 distributor_id 外键的所有电影。

defmodule Example.Movie do
  use Ecto.Schema

  schema "movies" do
    field :title, :string
    field :tagline, :string
    has_many :characters, Example.Character
    belongs_to :distributor, Example.Distributor
  end
end

defmodule Example.Distributor do
  use Ecto.Schema

  schema "distributors" do
    field :name, :string
    has_many :movies, Example.Movie
  end
end

如何为 has_one / belongs_to_many 关联定义 Elixir Ecto 架构？

How do I define Elixir Ecto schema for a has_one / belongs_to_many association?

associations

elixir

polymorphic-associations

ecto