One of the requirements of the Book Club exercise on elixirland.dev is to seed data.
I am referring to this requirement in the exercise.
## Requirements
...
### **Seeding**
* Running mix ecto.setup creates the database tables but also seeds the database
* Seeding inserts 4,000 books that each have 10 pages
* Some seeded books have an active page, but not all
* Seeding is fast
How happy or unhappy would you be if a co-worker would create a pull request containing this seeds.exs? Is it written in idiomatic Elixir? Use of comments, etc.
import Ecto.Query, only: [from: 2]
alias BookClub.Repo
alias BookClub.Books.{Book, Page}
# Setup
# Sets log level to :info for performance
initial_log_level = Logger.level()
Logger.configure(level: :info)
IO.puts("Start database seeding")
start_time = System.os_time(:millisecond)
# Constants
n_books = 4000
n_pages_per_book = 10
inserted_at = NaiveDateTime.utc_now(:second)
batch_size = 800
# Insert 4,000 books
books =
for _ <- 1..n_books do
%{
title: XlFaker.generate_title(),
inserted_at: inserted_at,
updated_at: inserted_at
}
end
books
|> Enum.chunk_every(batch_size)
|> Enum.each(&Repo.insert_all(Book, &1))
# Batch insert 10 pages per book
# Gives some books an active page
book_ids =
from(b in Book, select: b.id)
|> Repo.all()
pages =
book_ids
|> Enum.flat_map(fn book_id ->
pages =
for i <- 1..n_pages_per_book do
%{
book_id: book_id,
content: XlFaker.generate_page(),
number: i,
status: :inactive,
inserted_at: inserted_at,
updated_at: inserted_at
}
end
List.update_at(
pages,
:rand.uniform(n_pages_per_book) - 1,
&Map.put(&1, :status, Enum.random([:active, :inactive]))
)
end)
pages
|> Enum.chunk_every(batch_size)
|> Enum.each(&Repo.insert_all(Page, &1))
# Teardown
end_time = System.os_time(:millisecond)
IO.puts("Finish database seeding")
IO.puts("Seeded #{n_books} books in #{end_time - start_time}ms")
Logger.configure(level: initial_log_level)
