blockscout/lib/explorer_web/controllers/chain_controller.ex

defmodule ExplorerWeb.ChainController do
  use ExplorerWeb, :controller
  import Ecto.Query
  alias Explorer.Block
  alias Explorer.Transaction
  alias Explorer.Repo
  alias Explorer.BlockForm
  alias Explorer.TransactionForm

  def show(conn, _params) do
    blocks = Block
      |> order_by(desc: :number)
      |> limit(5)
      |> Repo.all
      |> Enum.map(&BlockForm.build/1)

    transactions = Transaction
      |> join(:left, [t, b], b in assoc(t, :block))
      |> order_by([t, b], desc: b.number)
      |> limit(5)
      |> Repo.all
      |> Repo.preload(:block)
      |> Enum.map(&TransactionForm.build/1)

    render(conn, "show.html", blocks: blocks, transactions: transactions)
  end
end