nietaki

import_if_available(Ecto.Query)
# alias MyApp.Repo

defmodule R do
  # Old habits die hard. Take a random of something. You don't care which.
  # > R.take(SomeSchema)
  def take(schema_or_query) do
    schema_or_query
    |> limit(1)
    |> Repo.one()

nietaki

$ lspci -nn
00:00.0 Host bridge [0600]: Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor Host Bridge/DRAM Registers [8086:191f] (rev 07)
00:01.0 PCI bridge [0604]: Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor PCIe Controller (x16) [8086:1901] (rev 07)
00:14.0 USB controller [0c03]: Intel Corporation 100 Series/C230 Series Chipset Family USB 3.0 xHCI Controller [8086:a12f] (rev 31)
00:16.0 Communication controller [0780]: Intel Corporation 100 Series/C230 Series Chipset Family MEI Controller #1 [8086:a13a] (rev 31)
00:17.0 SATA controller [0106]: Intel Corporation Q170/Q150/B150/H170/H110/Z170/CM236 Chipset SATA Controller [AHCI Mode] [8086:a102] (rev 31)
00:1b.0 PCI bridge [0604]: Intel Corporation 100 Series/C230 Series Chipset Family PCI Express Root Port #17 [8086:a167] (rev f1)
00:1b.2 PCI bridge [0604]: Intel Corporation 100 Series/C230 Series Chipset Family PCI Express Root Port #19 [8086:a169] (rev f1)
00:1c.0 PCI bridge [0604]: Intel Corporation 100 Series/C23

nietaki

#!/usr/bin/env bash

if [[ $# -eq 0 ]] ; then
    echo 'missing directory'
    exit 1
fi

dir="$1"

for filename in $dir/*.wav; do

nietaki

def category_preloader(category_names) when is_list(category_names) do
  # category_names are already deduplicated
  Enum.map(category_names, &RemoteService.retrieve_category_info/1)
end

query =
  from(p in Post,
    where: p.id in ^post_ids,
    preload: [category: ^&category_preloader/1]
  )

nietaki

defmodule BlogExample.Schema.Category do
  use Ecto.Schema

  @primary_key {:name, :string, []}

  embedded_schema do
    field(:current_popularity, :integer)
  end
end

nietaki

query =
  from(p in PostWithVirtualCategory,
    where: p.id in ^post_ids
  )

posts =
  query
  |> Repo.all()
  |> Enum.map(&PostWithVirtualCategory.populate_category/1)

nietaki

defmodule BlogExample.Schema.PostWithVirtualCategory do
  use Ecto.Schema

  schema "posts" do
    field(:title, :string, null: false)
    field(:contents, :string, null: false)
    field(:category_name, :string)

    field(:category, :map, virtual: true)

nietaki

    simpler_query = from(c in Comment, where: c.user_id == ^charlie_id)
    non_preloaded = Repo.all(simpler_query)
    assert Enum.all?(non_preloaded, fn c -> c.post == nil end)
    
    comments_by_charlie = Repo.preload(non_preloaded, [:post])
    refute Enum.any?(comments_by_charlie, fn c -> c.post == nil end)

nietaki

# aliases and imports omitted

query =
  from(c in Comment,
    where: c.user_id == ^charlie_id,
    preload: [:post]
  )

comments_by_charlie = Repo.all(query)
refute Enum.any?(comments_by_charlie, fn c -> c.post == nil end)

nietaki

alias BlogExample.Schema.Comment
import Ecto.Query, only: [from: 2]

query =
  from(c in Comment,
    where: c.user_id == ^charlie_id
  )

comments_by_charlie = Repo.all(query)