Question

在Rails中，我们可以在飞行中连接到多个数据库，

ActiveRecord::Base.establish_connection(
  database: "db_name", username: "postgres")

但是在Elixir - Phoenix框架中，如何做同样的过程。

Answer 1

use Mix.Config

config :my_app, MyApp.OneRepo,
  adapter: Ecto.Adapters.MySQL,
  database: "legacy_db",
  username: "username",
  password: "password",
  hostname: "something.com"

config :my_app, MyApp.TwoRepo,
  adapter: Ecto.Adapters.Postgres,
  username: "username",
  password: "password",
  database: "some_db_two",
  hostname: "example.com"

config :my_app, ecto_repos: [MyApp.OneRepo, MyApp.TwoRepo]

LIB / my_app.ex 监督回购。

defmodule Databases do
  use Application

  def start(_type, _args) do
    import Supervisor.Spec, warn: false

    children = [
      supervisor(MyApp.OneRepo, []), # <-- our addition
      supervisor(MyApp.TwoRepo, [])     # <-- our addition
    ]

    opts = [strategy: :one_for_one, name: MyApp.Supervisor]
    Supervisor.start_link(children, opts)
  end
end

最后 LIB / repos.ex

defmodule MyApp.OneRepo do
 use Ecto.Repo, otp_app: :my_app
end

defmodule MyApp.TwoRepo do
 use Ecto.Repo, otp_app: :my_app
end

例如

iex> import Ecto.Query



 iex> some_table= MyApp.OneRepo.get_by(SomeTable, %{username: "Alpha"})

iex> other_table= MyApp.TwoRepo.all from ot in OtherTable,
             where: ot.user_id == ^user.id

Answer 2

对于原始连接，需要使用比Ecto提供的更低的抽象级别。 Ecto代码是good source to take an inspiration from。基本上，对于MySQL数据库，应该这样做：

with {:ok, conn} <- Mariaex.start_link(opts) do
  value = Ecto.Adapters.MySQL.Connection.execute(conn, sql, [], opts)
  GenServer.stop(conn)
  value
end

其中opts是包含database，username等密钥的关键字列表。如何维护连接池的示例也可能从Ecto适配器源代码中被盗。

连接到多个数据库灵丹妙药

2 个答案: