Starman3787

Starman3787

DBConnection Compilation Error

hey,

i’m new to elixir so am very unfamiliar with how it all works

i am trying to connect to a MariaDB database using the mariaex driver

i’ve added it to the mix.exs file, as shown:

defmodule Backend.MixProject do
  use Mix.Project

  def project do
    [
      app: :backend,
      version: "0.1.0",
      elixir: "~> 1.9",
      start_permanent: Mix.env() == :prod,
      deps: deps()
    ]
  end

  def application do
    [
      mod: {Backend.Application, []},
      extra_applications: [:logger, :cowboy, :plug, :poison]
    ]
  end

  defp deps do
    [
      {:plug_cowboy, "~> 1.0.0"},
      {:poison, "~> 3.1"},
      {:mariaex, "~> 0.9.1"}
    ]
  end
end

…and i’ve also run mix deps.get

within the application.ex file (where Backend.Application is defined), i have included the line:

Mariaex.start_link(hostname: "localhost", port: "3307", username: "removed", password: "removed", database: "removed")

which according to the docs, should start a connection to the database

however when running iex -S mix in order to run the program, this compilation error is returned:

== Compilation error in file lib/backend/application.ex ==
** (exit) exited in: GenServer.call(DBConnection.Watcher, {:watch, DBConnection.ConnectionPool.Supervisor, {DBConnection.ConnectionPool.Pool, {#PID<0.190.0>, #Reference<0.1191833633.3142189059.94268>, Mariaex.Protocol, [hostname: "localhost", port: "3307", username: "removed", password: "removed", database: "removed"]}}}, :infinity)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started

and i have no clue what to do to fix this, nor can i find any solutions

any pointers or suggestions for what i could do or try would be hugely appreciated

Marked As Solved

josevalim

josevalim

Creator of Elixir

Can you please include the whole application file? You should start the connection to the database inside the start/2 function, typically as part of the supervision tree. Use mix new my_app —sup to have a better idea. Then, in children, you will do something like this:

{Mariaex, name: :my_app, password: …, …}

Also Liked

Starman3787

Starman3787

thanks for the response, this seems to work now:

defmodule Backend.Application do
  @moduledoc false

  use Application

  def start(_type, _args) do

    children = [
      Plug.Adapters.Cowboy.child_spec(scheme: :http, plug: Backend.Router, options: [port: 8085]),
      Mariaex.child_spec(hostname: "localhost", port: "3307", username: "removed", password: "removed", database: "removed")
    ]
    IO.puts("Worker started on port 8085")

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

i had called the Maria.start_link() function above the line use Application, which in hindsight seems like a very obvious and careless mistake now on my part

i’ve tried to write this in the way you said, i assume this is what you meant by “supervision tree”?

josevalim

josevalim

Creator of Elixir

Yes, that’s the way to go. I think you are only missing the name option, which you will pass as argument to Mariaex.query functions and similar.

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