TIL, 2018-03-18, Ecto.

import Ecto.Changeset to fix undefined function cast/3. This comes from the changeset part of Ecto. Remember, import so they can be called without the prefix.

user
|> Ecto.Changeset.cast(attrs, [:title, :description]) → |> cast(attrs, [:title, :description])
|> Ecto.Changeset.validate_required([:title, :description])

undefined_function has_many/1: has_many/2 exists. You need to hardcode the class where the assoc is going to. has_many :habits, HabitsTwo.Habit
pry in pipe operator

def foo do
  1..10
  |> Enum.map(&(&1 * &1))
  |> Enum.filter(&rem(&1, 2) == 0) |> pry
  |> Enum.take(3)
end

defp pry(e) do
  require IEx
  IEx.pry
  e
end

Debugging in pipe
Last record in Ecto: Repo.one(User)
Get last record in Ecto in iex: Habit > Ecto.Query.last > Repo.all
Get first record in Ecto in iex: Habit > Ecto.Query.first > Repo.all
cannot use ^user_id outside of match clauses: Usually a sign that you haven’t imported appropriate macros from Ecto.Query.
Phoenix token?
Composable queries in Ecto.

defmodule MyApp.Comment do
  # First post query so it's pipe-able
  def for_post(query, post) do
    from c in query,
    join: p in assoc(c, :post)
    where: p.id == ^post.id
  end

  def popular(query) do
    query |> where([c], c.votes > 10)
  end
end

recent_popular_comments = Comment
|> Comment.for_post(last_post)
|> Comment.popular
|> MyApp.Repo.all