"超级简单！Elixir和ScyllaDB教你创建CRUD CLI，惊人的效率提升！"

$ asdf plugin add erlang https://github.com/asdf-vm/asdf-erlang.git

$ asdf install erlang latest

$ asdf global erlang latest

$ asdf plugin-add elixir https://github.com/asdf-vm/asdf-elixir.git

$ asdf install elixir latest

$ asdf global elixir latest

Erlang/OTP 25 [erts-13.2.2.2] [source] [64-bit]

Elixir 1.13.4 (compiled with Erlang/OTP 23)

$ docker run --name some-scylla -p 9042:9042 -d scylladb/scylla

$ docker exec -it some-scylla cqlsh

Connected to at 172.17.0.2:9042.
[cqlsh 5.0.1 | Cassandra 3.0.8 | CQL spec 3.3.1 | Native protocol v4]
Use HELP for help.
cqlsh> 

cqlsh> DESCRIBE KEYSPACES;

system_schema system_traces system_distributed

cqlsh> CREATE KEYSPACE media_player
     WITH replication = {'class': 'NetworkTopologyStrategy', 'replication_factor': '3'}
     AND durable_writes = true;

cqlsh> CREATE TABLE media_player.songs (
     id uuid,
     titletext,
     album text,
     artist text,
     created_at timestamp,
     PRIMARY KEY (id, created_at)
);

$ mix new media_player

.
├── README.md
├── lib
│   └── media_player.ex
├── mix.exs

# Run "mix help deps" to learn about dependencies.
defp deps
  [
    {:dotenv, "~> 3.0"},
    {:decimal, "~> 1.0"},
    {:xandra, "~> 0.14"},
    {:elixir_uuid, "~> 1.2"}
  ]
end

$ mix deps.get

SCYLLADB_USERNAME=
SCYLLADB_PASSWORD=
SCYLLADB_NODE=
SCYLLADB_KEYSPACE=
SCYLLADB_TABLE=

SCYLLADB_USERNAME=scylla
SCYLLADB_PASSWORD=scylla
SCYLLADB_NODE=localhost:9042
SCYLLADB_KEYSPACE=media_player
SCYLLADB_TABLE=songs

.
├── README.md
├── lib
│   ├── media_player
│   │   └── config
│   │   ├── connection.ex
│   │   └── database.ex
│   └── media_player.ex
├── mix.exs

defmodule MediaPlayer.Config.Database do
  import Dotenv

  load()

  def start_link do
    options = [
      username: System.get_env("SCYLLADB_USERNAME"),
      password: System.get_env("SCYLLADB_PASSWORD")
    ]

    {:ok, cluster} =
      Xandra.Cluster.start_link(
        sync_connect: :infinity,
        authentication: {Xandra.Authenticator.Password, options},
        nodes:
          System.get_env("SCYLLADB_NODE")
          |> String.split(",")
      )

    cluster
  end
end

defmodule MediaPlayer.Config.Connection do
  import Dotenv

  load()

  def keyspace() do
    System.get_env("SCYLLADB_KEYSPACE")
  end

  def table() do
    System.get_env("SCYLLADB_TABLE")
  end
end

.
├── README.md
├── lib
│   ├── media_player
│   │   ├── actions.ex
│   │   └── config
│   │   ├── connection.ex
│   │   └── database.ex
│   └── media_player.ex
├── mix.exs

defmodule MediaPlayer.Actions do
  def cluster, do: MediaPlayer.Config.Database.start_link()

  def run_query(query) do
    case Xandra.Cluster.execute(cluster(), query) do
      {:ok, result} ->
        result

      {:error, error} ->
        IO.inspect(error)
    end
  end

  def run_query(query, params) do
    prepared = Xandra.Cluster.prepare!(cluster(), query)

    case Xandra.Cluster.execute(cluster(), prepared, params) do
      {:ok, result} ->
        result

      {:error, error} ->
        IO.inspect(error)
    end
  end
end

.
├── README.md
├── lib
│   ├── media_player
│   │   ├── actions.ex
│   │   ├── commands.ex
│   │   └── config
│   │   ├── connection.ex
│   │   └── database.ex
│   └── media_player.ex
├── mix.exs

defmodule MediaPlayer.Commands do
  alias MediaPlayer.Actions, as: Actions
  alias MediaPlayer.Config.Connection, as: Connection

  defp keyspace, do: Connection.keyspace()
  defp table, do: Connection.table()
end

defmodule MediaPlayer.Commands do
  alias MediaPlayer.Actions, as: Actions
  alias MediaPlayer.Config.Connection, as: Connection

  defp keyspace, do: Connection.keyspace()
  defp table, do: Connection.table()

  def add_from(title, album, artist, created) do
    query =
      "INSERT INTO #{keyspace()}.#{table()} (id, title, album, artist, created_at) VALUES (?, ?, ?, ?, ?);"

    {:ok, created, _} = DateTime.from_iso8601(created <> "T00:00:00Z")

    Actions.run_query(query, [UUID.uuid4(), title, album, artist, created])

    IO.puts("Song added!")
  end

  def add() do
    title = IO.gets("Enter the title of the song: ") |> String.trim()
    album = IO.gets("Enter the album of the song: ") |> String.trim()
    artist = IO.gets("Enter the artist of the song: ") |> String.trim()

    created =
      IO.gets("Enter the date the song was created (YYYY-MM-DD): ")
      |> String.trim()

    add_from(title, album, artist, created)
  end
end

  def list
    query = "SELECT id, title, album, artist, created_at FROM #{keyspace()}.#{table()};"

    Actions.run_query(query)
    |> Enum.each(fn %{
                      "id" => id,
                      "title" => title,
                      "album" => album,
                      "artist" => artist,
                      "created_at" => created_at
                    } ->
      IO.puts(
        "ID: #{id} | Title: #{title} | Album: #{album} | Artist: #{artist} | Created At: #{created_at}"
      )
    end)
  end

  def delete() do
    query = "SELECT id, title, album, artist, created_at FROM #{keyspace()}.#{table()};"

    songs =
      Actions.run_query(query)
      |> Enum.with_index(fn %{
                              "id" => id,
                              "title" => title,
                              "album" => album,
                              "artist" => artist,
                              "created_at" => created_at
                            },
                            index ->
        IO.puts(
          "Index: #{index + 1} | Title: #{title} | Album: #{album} | Artist: #{artist} | Created At: #{created_at}"
        )

        %{id: id, title: title, album: album, artist: artist, created_at: created_at}
      end)

    {input, _} = IO.gets("Enter the index of the song you want to delete: ") |> Integer.parse()

    case Enum.at(songs, input - 1) do
      %{} = song ->
        query = "DELETE FROM #{keyspace()}.#{table()} WHERE id = ? AND created_at = ?;"

        Actions.run_query(query, [song.id, song.created_at])

        IO.puts("Song deleted!")

      nil ->
        IO.puts("Invalid index.")
    end
  end

defmodule MediaPlayer.Commands do
  use Task
  ...

  defp generate_stress_query(some_id) do
    current_date = Date.to_string(Date.utc_today())

    "INSERT INTO #{keyspace()}.#{table()} (
      id, title, album, artist, created_at
    ) VALUES (
      #{UUID.uuid4()},
      'Test Song #{some_id}',
      'Test Artist #{some_id}',
      'Test Album #{some_id}',
      '#{current_date}'
    );"
  end

  def stress
    start = Time.utc_now()
    cluster = MediaPlayer.Config.Database.start_link()

    # Simple stress test
    1..100_000
    |> Task.async_stream(
      fn id ->
        IO.puts("[#{id}] Adding seed")
        Xandra.Cluster.execute(cluster, generate_stress_query(id))
      end,
      max_concurrency: 500
    )
    |> Enum.to_list()

    IO.puts("Time taken: #{Time.diff(Time.utc_now(), start, :second)} seconds")
  end

defmodule MediaPlayer
  alias MediaPlayer.Commands, as: Commands
end

  def loop do
    IO.puts("-------------------------------------")
    IO.puts("Type any command: ")
    command = IO.gets("") |> String.trim()

    case command do
      "!add" ->
        Commands.add()
        loop()

      "!list" ->
        Commands.list()
        loop()

      "!delete" ->
        Commands.delete()
        loop()

      "!stress" ->
        Commands.stress()
        loop()

      "exit" ->
        IO.puts("Bye bye!")
        :OK

      _ ->
        IO.puts("Command not found!")
        loop()
    end
  end

  def start(_, _) do
    run()
    {:ok, self()}
  end

  def run do
    IO.puts("-------------------------------------")
    IO.puts("- ScyllaDB Cloud Elixir Media Player -")
    IO.puts("- Leave a star on the repo -")
    IO.puts("-------------------------------------")
    IO.puts("Here some possibilities")
    IO.puts(" !add - add new song")
    IO.puts(" !list - list all songs")
    IO.puts(" !delete - delete a specific song")
    IO.puts(" !stress - stress testing with mocked data")
    IO.puts("-------------------------------------")

    loop()
  end

$ mix run