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elixirphoenix-frameworkecto

Use Ecto in a mix task

In a Phoenix Framework application I have a model Product with the field name. I want to create a mix task which lists all product names.

In Ruby on Rails this would be the code to solve the problem:

namespace :list do
  desc "List all products"
  task products: :environment do
    Product.all.each do |product|
      puts product.name
    end
  end
end

In Phoenix I can't even get the list of all products from the database. Here is the task code:

lib/mix/tasks/list.product.ex

defmodule Mix.Tasks.List.Product do                                    
  use Mix.Task
  import Mix.Ecto
  alias App.Repo
  alias App.Product

  def run(_args) do
    products = Repo.all(Product)
  end
end

When I run this task I get this error message:

** (UndefinedFunctionError) function Ecto.Queryable.__using__/1 
is undefined or private

What do I have to do to fetch all products from the database in this mix task?

Solution

  • The hard way:

    defmodule Mix.Tasks.MyTask do
  use Mix.Task
  import Ecto.Query
  alias MyApp.Repo

  @start_apps [
    :postgrex,
    :ecto,
    :ecto_sql
  ]

  @repos Application.get_env(:my_app, :ecto_repos, [])

  def run(args) do
    start_services()

    # Run Ecto...

    stop_services()
  end

  defp start_services do
    Enum.each(@start_apps, &Application.ensure_all_started/1)
    Enum.each(@repos, & &1.start_link(pool_size: 2))
  end

  defp stop_services do
    :init.stop()
  end
end

    or the easy way ;)

    defmodule Mix.Tasks.MyTask do
  use Mix.Task
  import Ecto.Query
  alias MyApp.Repo

  def run(args) do
    Mix.Task.run("app.start")
    # Run Ecto...
  end
end