{
  "id": "salary-crud/bubbly-baking-prism-subagent-ac41f0b",
  "slug": "bubbly-baking-prism-subagent-ac41f0b",
  "title": "Session: bubbly-baking-prism-subagent-ac41f0b — 2026-02-13",
  "type": "source",
  "project": "salary-crud",
  "date": "2026-02-13",
  "started": "2026-02-13T15:17:06.604000+00:00",
  "ended": "2026-02-13T15:17:57.245000+00:00",
  "model": "claude-haiku-4-5-20251001",
  "cwd": "/Users/USER/workspace/playground/employee-salary-crud",
  "git_branch": "main",
  "permission_mode": "",
  "user_messages": 1,
  "tool_calls": 27,
  "tools_used": [
    "Bash",
    "Read"
  ],
  "is_subagent": true,
  "wikilinks_out": [],
  "body_text": "Project: salary-crud · Branch: main · Mode:  · Model: claude-haiku-4-5-20251001\n\nStats: 1 user messages, 27 tool calls, tools used: Bash, Read.\n\nConversation\n\nTurn 1 — User\n\nI need to understand the existing code patterns in this Phoenix application to ensure the implementation plan follows the same conventions.\n\nInvestigate:\n1. How are the existing resources (Country, Currency) structured? Look at:\n   - Schema definitions (lib/be_exercise/countries/.ex)\n   - Context modules\n   - Controllers and JSON views (lib/be_exercise_web/controllers/)\n   - Test patterns\n\n2. What's the current router configuration?\n\n3. How is the seeds.exs file currently structured?\n\n4. What data files exist in priv/data/?\n\nThis will help validate the implementation plan's assumptions about code structure and conventions.\n\nTurn 1 — Assistant\n\nI'll systematically explore the Phoenix application to understand the existing code patterns. Let me start by examining the directory structure and then dive into the specific areas you mentioned.\n\nTools used:\n\n- Bash: find /Users/USER/workspace/playground/employee-salary-crud -type f -name \".ex\" -o -name \".exs\" | head -30\n\nTool results:\n\n  → result (ok): /Users/USER/workspace/playground/employee-salary-crud/mix.exs\n/Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/country_controller_test.exs\n/Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/error_json_test.exs\n/Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/currency_controller_test.exs\n/Users/USER/workspace/playground/employee-salary-crud/test/be_exercise/countries_test.exs\n/Users/USE\n…(truncated, 2532 more chars)\n\nLet me continue exploring the structure more thoroughly.\n\nTools used:\n\n- Bash: ls -la /Users/USER/workspace/playground/employee-salary-crud/lib/\n\nTool results:\n\n  → result (ok): drwxr-xr-x clertonra staff 192 B  Fri Feb 13 16:13:08 2026 .\ndrwxr-xr-x clertonra staff 512 B  Fri Feb 13 16:14:42 2026 ..\ndrwxr-xr-x clertonra staff 224 B  Fri Feb 13 16:13:08 2026 be_exercise\n.rw-r--r-- clertonra staff 253 B  Fri Feb 13 16:13:08 2026 be_exercise.ex\ndrwxr-xr-x clertonra staff 224 B  Fri Feb 13 16:13:08 2026 be_exercise_web\n.rw-r--r-- clertonra staff 2.2 KB Fri Feb 13 16:13:08 2026 be_exercise_web.ex\n\nTools used:\n\n- Bash: find /Users/USER/workspace/playground/employee-salary-crud/lib -type f -name \".ex\" | sort\n\nTool results:\n\n  → result (ok): /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web.ex\n/Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/changeset_json.ex\n/Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_controller.ex\n/Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_json.ex\n/Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/currency_controller.ex\n\n…(truncated, 1359 more chars)\n\nNow let me explore the specific files mentioned in your requirements:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/countries/country.ex\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.Countries.Country do\n     2→  use Ecto.Schema\n     3→  import Ecto.Changeset\n     4→\n     5→  schema \"countries\" do\n     6→    field :code, :string\n     7→    field :name, :string\n     8→\n     9→    timestamps()\n    10→  end\n    11→\n    12→  @doc false\n    13→  def changeset(country, attrs) do\n    14→    country\n    15→    |> cast(attrs, [:name, :code])\n    16→    |> validate_required([:name, :code])\n    17→    |> unique_constraint(:name)\n    18→    |> unique_constraint(:cod\n…(truncated, 373 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/countries/currency.ex\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.Countries.Currency do\n     2→  use Ecto.Schema\n     3→  import Ecto.Changeset\n     4→\n     5→  schema \"currencies\" do\n     6→    field :code, :string\n     7→    field :name, :string\n     8→    field :symbol, :string\n     9→\n    10→    timestamps()\n    11→  end\n    12→\n    13→  @doc false\n    14→  def changeset(currency, attrs) do\n    15→    currency\n    16→    |> cast(attrs, [:code, :name, :symbol])\n    17→    |> validate_required([:code, :name, :symbol])\n    18→    |> uniqu\n…(truncated, 429 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/countries.ex\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.Countries do\n     2→  @moduledoc \"\"\"\n     3→  The Countries context.\n     4→  \"\"\"\n     5→\n     6→  import Ecto.Query, warn: false\n     7→  alias Exercise.Repo\n     8→\n     9→  alias Exercise.Countries.Currency\n    10→\n    11→  @doc \"\"\"\n    12→  Returns the list of currencies.\n    13→\n    14→  ## Examples\n    15→\n    16→      iex> list_currencies()\n    17→      [%Currency{}, ...]\n    18→\n    19→  \"\"\"\n    20→  def list_currencies do\n    21→    Repo.all(Currency)\n    22→  end\n \n…(truncated, 5397 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/router.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.Router do\n     2→  use ExerciseWeb, :router\n     3→\n     4→  pipeline :api do\n     5→    plug :accepts, [\"json\"]\n     6→  end\n     7→\n     8→  scope \"/api\", ExerciseWeb do\n     9→    pipe_through :api\n    10→\n    11→    resources \"/currencies\", CurrencyController\n    12→    resources \"/countries\", CountryController\n    13→  end\n    14→\n    15→  # Enables LiveDashboard only for development\n    16→  #\n    17→  # If you want to use the LiveDashboard in production, you should\n…(truncated, 970 more chars)\n\nNow let me examine the controllers and JSON views:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_controller.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.CountryController do\n     2→  use ExerciseWeb, :controller\n     3→\n     4→  alias Exercise.Countries\n     5→  alias Exercise.Countries.Country\n     6→\n     7→  action_fallback ExerciseWeb.FallbackController\n     8→\n     9→  def index(conn, _params) do\n    10→    countries = Countries.list_countries()\n    11→    render(conn, :index, countries: countries)\n    12→  end\n    13→\n    14→  def create(conn, %{\"country\" => country_params}) do\n    15→    with {:ok, %Country{} = cou\n…(truncated, 1360 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_json.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.CountryJSON do\n     2→  alias Exercise.Countries.Country\n     3→\n     4→  @doc \"\"\"\n     5→  Renders a list of countries.\n     6→  \"\"\"\n     7→  def index(%{countries: countries}) do\n     8→    %{data: for(country <- countries, do: data(country))}\n     9→  end\n    10→\n    11→  @doc \"\"\"\n    12→  Renders a single country.\n    13→  \"\"\"\n    14→  def show(%{country: country}) do\n    15→    %{data: data(country)}\n    16→  end\n    17→\n    18→  defp data(%Country{} = country) do\n  \n…(truncated, 489 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/currency_controller.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.CurrencyController do\n     2→  use ExerciseWeb, :controller\n     3→\n     4→  alias Exercise.Countries\n     5→  alias Exercise.Countries.Currency\n     6→\n     7→  action_fallback ExerciseWeb.FallbackController\n     8→\n     9→  def index(conn, _params) do\n    10→    currencies = Countries.list_currencies()\n    11→    render(conn, :index, currencies: currencies)\n    12→  end\n    13→\n    14→  def create(conn, %{\"currency\" => currency_params}) do\n    15→    with {:ok, %Currenc\n…(truncated, 1396 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/currency_json.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.CurrencyJSON do\n     2→  alias Exercise.Countries.Currency\n     3→\n     4→  @doc \"\"\"\n     5→  Renders a list of currencies.\n     6→  \"\"\"\n     7→  def index(%{currencies: currencies}) do\n     8→    %{data: for(currency <- currencies, do: data(currency))}\n     9→  end\n    10→\n    11→  @doc \"\"\"\n    12→  Renders a single currency.\n    13→  \"\"\"\n    14→  def show(%{currency: currency}) do\n    15→    %{data: data(currency)}\n    16→  end\n    17→\n    18→  defp data(%Currency{} = c\n…(truncated, 544 more chars)\n\nNow let me check the test patterns and migration files:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise/countries_test.exs\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.CountriesTest do\n     2→  use Exercise.DataCase\n     3→\n     4→  alias Exercise.Countries\n     5→\n     6→  describe \"currencies\" do\n     7→    alias Exercise.Countries.Currency\n     8→\n     9→    @valid_attrs %{code: \"some code\", name: \"some name\", symbol: \"some symbol\"}\n    10→    @update_attrs %{\n    11→      code: \"some updated code\",\n    12→      name: \"some updated name\",\n    13→      symbol: \"some updated symbol\"\n    14→    }\n    15→    @invalid_attrs %{code: nil, name\n…(truncated, 5358 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/country_controller_test.exs\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.CountryControllerTest do\n     2→  use ExerciseWeb.ConnCase\n     3→\n     4→  alias Exercise.Countries\n     5→  alias Exercise.Countries.Country\n     6→\n     7→  @create_attrs %{\n     8→    code: \"some code\",\n     9→    name: \"some name\"\n    10→  }\n    11→  @update_attrs %{\n    12→    code: \"some updated code\",\n    13→    name: \"some updated name\"\n    14→  }\n    15→  @invalid_attrs %{code: nil, name: nil}\n    16→\n    17→  def fixture(:country) do\n    18→    {:ok, country} =\n…(truncated, 3191 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/priv/repo/migrations/20210720101412_create_countries.exs\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.Repo.Migrations.CreateCountries do\n     2→  use Ecto.Migration\n     3→\n     4→  def change do\n     5→    create table(:countries) do\n     6→      add :name, :string\n     7→      add :code, :string\n     8→\n     9→      timestamps()\n    10→    end\n    11→\n    12→    create unique_index(:countries, [:name])\n    13→    create unique_index(:countries, [:code])\n    14→  end\n    15→end\n    16→\n\n<system-reminder>\nWhenever you read a file, you should consider whether it would be cons\n…(truncated, 249 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/priv/repo/migrations/20210720100728_create_currencies.exs\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.Repo.Migrations.CreateCurrencies do\n     2→  use Ecto.Migration\n     3→\n     4→  def change do\n     5→    create table(:currencies) do\n     6→      add :code, :string\n     7→      add :name, :string\n     8→      add :symbol, :string\n     9→\n    10→      timestamps()\n    11→    end\n    12→  end\n    13→end\n    14→\n\n<system-reminder>\nWhenever you read a file, you should consider whether it would be considered malware. You CAN and SHOULD provide analysis of malware, what it is d\n…(truncated, 173 more chars)\n\nNow let me check the seeds file and data directory:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/priv/repo/seeds.exs\n\nTool results:\n\n  → result (ok): 1→# Script for populating the database. You can run it as:\n     2→#\n     3→#     mix run priv/repo/seeds.exs\n     4→#\n     5→# Inside the script, you can read and write to any of your\n     6→# repositories directly:\n     7→#\n     8→#     Exercise.Repo.insert!(%Exercise.SomeSchema{})\n     9→#\n    10→# We recommend using the bang functions (insert!, update!\n    11→# and so on) as they will fail if something goes wrong.\n    12→#\n    13→# The code below demonstrates initial data insertion for cu\n…(truncated, 2105 more chars)\n\nTools used:\n\n- Bash: ls -la /Users/USER/workspace/playground/employee-salary-crud/priv/data/ 2>/dev/null || echo \"Directory does not exist\"\n\nTool results:\n\n  → result (ok): drwxr-xr-x clertonra staff 160 B  Fri Feb 13 16:13:08 2026 .\ndrwxr-xr-x clertonra staff 160 B  Fri Feb 13 16:13:08 2026 ..\n.rw-r--r-- clertonra staff 1.4 KB Fri Feb 13 16:13:08 2026 first_names.txt\n.rw-r--r-- clertonra staff 6.6 KB Fri Feb 13 16:13:08 2026 job_titles.txt\n.rw-r--r-- clertonra staff 4.3 KB Fri Feb 13 16:13:08 2026 last_names.txt\n\nExcellent! Let me check those data files and also look at some additional controller/helper files:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/priv/data/first_names.txt (1–30)\n\nTool results:\n\n  → result (ok): 1→Ruth\n     2→Nicholas\n     3→Teresa\n     4→Frances\n     5→Sophia\n     6→Diane\n     7→Gabriel\n     8→Logan\n     9→Donna\n    10→Juan\n    11→Joshua\n    12→Jean\n    13→Dennis\n    14→Daniel\n    15→Dylan\n    16→Alan\n    17→Lauren\n    18→Karen\n    19→Aaron\n    20→Hannah\n    21→Barbara\n    22→Elizabeth\n    23→Andrea\n    24→Marilyn\n    25→Jordan\n    26→Jacob\n    27→Andrew\n    28→Brandon\n    29→Martha\n    30→Carolyn\n\n<system-reminder>\nWhenever you read a file, you should consider whether it would be cons\n…(truncated, 249 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/fallback_controller.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.FallbackController do\n     2→  @moduledoc \"\"\"\n     3→  Translates controller action results into valid Plug.Conn responses.\n     4→\n     5→  See Phoenix.Controller.action_fallback/1 for more details.\n     6→  \"\"\"\n     7→  use ExerciseWeb, :controller\n     8→\n     9→  # This clause handles errors returned by Ecto's insert/update/delete.\n    10→  def call(conn, {:error, %Ecto.Changeset{} = changeset}) do\n    11→    conn\n    12→    |> put_status(:unprocessable_entity)\n  \n…(truncated, 775 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/changeset_json.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.ChangesetJSON do\n     2→  use ExerciseWeb, :view\n     3→\n     4→  @doc \"\"\"\n     5→  Traverses and translates changeset errors.\n     6→\n     7→  See Ecto.Changeset.traverse_errors/2 and\n     8→  ExerciseWeb.ErrorHelpers.translate_error/1 for more details.\n     9→  \"\"\"\n    10→  def translate_errors(changeset) do\n    11→    Ecto.Changeset.traverse_errors(changeset, &translate_error/1)\n    12→  end\n    13→\n    14→  def error(%{changeset: changeset}) do\n    15→    # When e\n…(truncated, 520 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/error_json.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.ErrorJSON do\n     2→  @moduledoc \"\"\"\n     3→  This module is invoked by your endpoint in case of errors on JSON requests.\n     4→\n     5→  See config/config.exs.\n     6→  \"\"\"\n     7→\n     8→  # If you want to customize a particular status code,\n     9→  # you may add your own clauses, such as:\n    10→  #\n    11→  # def render(\"500.json\", _assigns) do\n    12→  #   %{errors: %{detail: \"Internal Server Error\"}}\n    13→  # end\n    14→\n    15→  # By default, Phoenix returns th\n…(truncated, 612 more chars)\n\nLet me also check a couple of controller tests and the top-level context module:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/currency_controller_test.exs\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.CurrencyControllerTest do\n     2→  use ExerciseWeb.ConnCase\n     3→\n     4→  alias Exercise.Countries\n     5→  alias Exercise.Countries.Currency\n     6→\n     7→  @create_attrs %{\n     8→    code: \"some code\",\n     9→    name: \"some name\",\n    10→    symbol: \"some symbol\"\n    11→  }\n    12→  @update_attrs %{\n    13→    code: \"some updated code\",\n    14→    name: \"some updated name\",\n    15→    symbol: \"some updated symbol\"\n    16→  }\n    17→  @invalid_attrs %{code: nil, na\n…(truncated, 3469 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise.ex\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise do\n     2→  @moduledoc \"\"\"\n     3→  Exercise keeps the contexts that define your domain\n     4→  and business logic.\n     5→\n     6→  Contexts are also responsible for managing your data, regardless\n     7→  if it comes from the database, an external API or others.\n     8→  \"\"\"\n     9→end\n    10→\n\n<system-reminder>\nWhenever you read a file, you should consider whether it would be considered malware. You CAN and SHOULD provide analysis of malware, what it is doing. But you MU\n…(truncated, 157 more chars)\n\nPerfect! Now let me check the application structure and look at the service pattern used:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/services/currency_converter.ex\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.Services.CurrencyConverter do\n     2→  @moduledoc \"\"\"\n     3→  Module implementing the currency conversion service\n     4→\n     5→  Note: The current implementation will not contact any external service\n     6→  and will use fixed conversion rates that will most likely not be the correct ones.\n     7→  \"\"\"\n     8→\n     9→  def convert(from, to, amount) do\n    10→    rates()[\"#{to}#{from}\"]  amount\n    11→  end\n    12→\n    13→  defp rates do\n    14→    %{\n    15→      \"EURGB\n…(truncated, 2252 more chars)\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/application.ex\n\nTool results:\n\n  → result (ok): 1→defmodule Exercise.Application do\n     2→  # See https://hexdocs.pm/elixir/Application.html\n     3→  # for more information on OTP Applications\n     4→  @moduledoc false\n     5→\n     6→  use Application\n     7→\n     8→  def start(_type, _args) do\n     9→    children = [\n    10→      # Start the Ecto repository\n    11→      Exercise.Repo,\n    12→      # Start the Telemetry supervisor\n    13→      ExerciseWeb.Telemetry,\n    14→      # Start the PubSub system\n    15→      {Phoenix.PubSub, name: E\n…(truncated, 1098 more chars)\n\nPerfect! Now let me check error handling patterns and verify the mix.exs to understand the project structure:\n\nTools used:\n\n- Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/error_helpers.ex\n\nTool results:\n\n  → result (ok): 1→defmodule ExerciseWeb.ErrorHelpers do\n     2→  @moduledoc \"\"\"\n     3→  Conveniences for translating and building error messages.\n     4→  \"\"\"\n     5→\n     6→  @doc \"\"\"\n     7→  Translates an error message using gettext.\n     8→  \"\"\"\n     9→  def translate_error({msg, opts}) do\n    10→    # When using gettext, we typically pass the strings we want\n    11→    # to translate as a static argument:\n    12→    #\n    13→    #     # Translate \"is invalid\" in the \"errors\" domain\n    14→    #     dgette\n…(truncated, 1285 more chars)\n\nTools used:\n\n- Bash: head -50 /Users/USER/workspace/playground/employee-salary-crud/mix.exs\n\nTool results:\n\n  → result (ok): defmodule Exercise.MixProject do\n  use Mix.Project\n\n  def project do\n    [\n      app: :be_exercise,\n      version: \"0.1.0\",\n      elixir: \"~> 1.18\",\n      elixirc_paths: elixirc_paths(Mix.env()),\n      compilers: Mix.compilers(),\n      start_permanent: Mix.env() == :prod,\n      aliases: aliases(),\n      deps: deps(),\n      listeners: [Phoenix.CodeReloader]\n    ]\n  end\n\n  # Configuration for the OTP application.\n  #\n  # Type mix help compile.app for more information.\n  def application do\n    [\n\n…(truncated, 786 more chars)\n\nExcellent! Now I have comprehensive understanding of the codebase. Let me compile my findings into a detailed report.\n\nCode Pattern Analysis - Phoenix Application Investigation\n\nBased on my thorough examination of the existing codebase, here's a comprehensive analysis of the patterns and conventions used in this Phoenix application:\n\n1. Project Structure & Naming Conventions\n\nModule Namespacing:\n- Top-level app module: Exercise (defined in lib/be_exercise.ex)\n- Web module: ExerciseWeb (defined in lib/be_exercise_web.ex)\n- All app files use be_exercise prefix in directory names\n- All web files use be_exercise_web prefix in directory names\n\nNotable: The module names (Exercise, ExerciseWeb) don't match the directory prefixes (be_exercise, be_exercise_web). This is important for the Employee module naming.\n\n2. Schema Definitions\n\nPattern Found (lib/be_exercise/countries/country.ex and currency.ex):\ndefmodule Exercise.Countries.Country do\n  use Ecto.Schema\n  import Ecto.Changeset\n\n  schema \"countries\" do\n    field :code, :string\n    field :name, :string\n    timestamps()\n  end\n\n  @doc false\n  def changeset(entity, attrs) do\n    entity\n    |> cast(attrs, [:name, :code])\n    |> validate_required([:name, :code])\n    |> unique_constraint(:name)\n    |> unique_constraint(:code)\n  end\nend\n\nKey Conventions:\n- Schemas nested under context modules in subdirectories (countries/country.ex)\n- All fields are typed (typically :string)\n- Timestamps always included\n- Changesets implement validation + uniqueness constraints\n- @doc false on changesets (private docs)\n\n3. Context Module Pattern\n\nStructure (lib/be_exercise/countries.ex):\n- Single context file for related resources (Countries context handles both Country and Currency)\n- Functions follow naming pattern: list_<resource>, get_<resource>!, create_<resource>, update_<resource>, delete_<resource>, change_<resource>\n- All public functions have @doc with examples (iex format)\n- Uses Ecto.Query for custom queries with where clauses\n- Direct Repo.all, Repo.get!, Repo.insert, Repo.update, Repo.delete calls\n\nFunctions provided:\n- List operations (list_currencies, list_countries)\n- Get by ID (get_currency!, get_country!)\n- Get by attribute (get_currency_by_code!)\n- CRUD operations (create_, update_, delete_)\n- Change tracking (change_currency, change_country)\n\n4. Controller Pattern\n\nStructure (lib/be_exercise_web/controllers/country_controller.ex):\ndefmodule ExerciseWeb.CountryController do\n  use ExerciseWeb, :controller\n\n  alias Exercise.Countries\n  alias Exercise.Countries.Country\n\n  action_fallback ExerciseWeb.FallbackController\n\n  # index, create, show, update, delete actions\nend\n\nKey Conventions:\n- use ExerciseWeb, :controller macro\n- Aliases for context and schema\n- action_fallback decorator for error handling\n- Standard RESTful actions: index, create, show, update, delete\n- Use with pattern for error handling\n- HTTP status codes: :created (201) for create, :no_content (204) for delete\n- Response headers set with put_resp_header for create (location)\n- Parameters wrapped in resource name: %{\"country\" => country_params}\n\n5. JSON View/Renderer Pattern\n\nStructure (lib/be_exercise_web/controllers/country_json.ex):\ndefmodule ExerciseWeb.CountryJSON do\n  alias Exercise.Countries.Country\n\n  def index(%{countries: countries}) do\n    %{data: for(country <- countries, do: data(country))}\n  end\n\n  def show(%{country: country}) do\n    %{data: data(country)}\n  end\n\n  defp data(%Country{} = country) do\n    %{\n      id: country.id,\n      name: country.name,\n      code: country.code\n    }\n  end\nend\n\nKey Conventions:\n- Module named <Resource>JSON\n- Functions match controller actions: index, show\n- All responses wrapped in %{data: ...} structure\n- Private data/1 function for individual resource rendering\n- Only specific fields exposed (ID, name, code, etc.) - no timestamps or auto-fields\n\n6. Router Configuration\n\nPattern (lib/be_exercise_web/router.ex):\ndefmodule ExerciseWeb.Router do\n  use ExerciseWeb, :router\n\n  pipeline :api do\n    plug :accepts, [\"json\"]\n  end\n\n  scope \"/api\", ExerciseWeb do\n    pipe_through :api\n\n    resources \"/currencies\", CurrencyController\n    resources \"/countries\", CountryController\n  end\nend\n\nKey Conventions:\n- API routes nested under /api scope\n- Uses resources macro for RESTful routing\n- Controllers in scope automatically use ExerciseWeb module prefix\n- Single api pipeline for JSON requests\n\n7. Error Handling & Fallback\n\nFallbackController (lib/be_exercise_web/controllers/fallback_controller.ex):\ndef call(conn, {:error, %Ecto.Changeset{} = changeset}) do\n  conn\n  |> put_status(:unprocessable_entity)\n  |> put_view(json: ExerciseWeb.ChangesetJSON)\n  |> render(\"error.json\", changeset: changeset)\nend\n\nChangesetJSON (lib/be_exercise_web/controllers/changeset_json.ex):\ndef error(%{changeset: changeset}) do\n  %{errors: translate_errors(changeset)}\nend\n\nKey Conventions:\n- :unprocessable_entity (422) for validation errors\n- Errors wrapped in %{errors: {...}} structure\n- Uses translate_error/1 from ErrorHelpers\n- Gettext integration for i18n\n\n8. Migration Pattern\n\nStructure (priv/repo/migrations/20210720101412_create_countries.exs):\ndefmodule Exercise.Repo.Migrations.CreateCountries do\n  use Ecto.Migration\n\n  def change do\n    create table(:countries) do\n      add :name, :string\n      add :code, :string\n      timestamps()\n    end\n\n    create unique_index(:countries, [:name])\n    create unique_index(:countries, [:code])\n  end\nend\n\nKey Conventions:\n- Module name matches timestamp prefix: YYYYMMDDhhmmss_action\n- Uses Ecto.Migration\n- Unique indices created directly in migration (matching schema constraints)\n- timestamps() automatically added\n- Field order: code first, then name (for currencies)\n\n9. Test Pattern - Context Tests\n\nStructure (test/be_exercise/countries_test.exs):\ndefmodule Exercise.CountriesTest do\n  use Exercise.DataCase\n\n  describe \"currencies\" do\n    @valid_attrs %{code: \"some code\", name: \"some name\", symbol: \"some symbol\"}\n    @update_attrs %{...}\n    @invalid_attrs %{code: nil, name: nil, symbol: nil}\n\n    def currency_fixture(attrs \\\\ %{}) do\n      {:ok, currency} = Countries.create_currency(attrs |> Enum.into(@valid_attrs))\n      currency\n    end\n\n    test \"list_currencies/0 returns all currencies\" do\n      # test body\n    end\n  end\nend\n\nKey Conventions:\n- Uses Exercise.DataCase (not ExerciseWeb.ConnCase for context tests)\n- Module attributes for valid/update/invalid data\n- Fixture functions for creating test data\n- describe blocks for grouping related tests\n- Tests for each context function: list, get, create, update, delete, change\n\n10. Test Pattern - Controller Tests\n\nStructure (test/be_exercise_web/controllers/country_controller_test.exs):\ndefmodule ExerciseWeb.CountryControllerTest do\n  use ExerciseWeb.ConnCase\n\n  setup %{conn: conn} do\n    {:ok, conn: put_req_header(conn, \"accept\", \"application/json\")}\n  end\n\n  describe \"index\" do\n    test \"lists all countries\", %{conn: conn} do\n      conn = get(conn, Routes.country_path(conn, :index))\n      assert json_response(conn, 200)[\"data\"] == []\n    end\n  end\n\n  describe \"create country\" do\n    test \"renders country when data is valid\", %{conn: conn} do\n      conn = post(conn, Routes.country_path(conn, :create), country: @create_attrs)\n      assert %{\"id\" => id} = json_response(conn, 201)[\"data\"]\n    end\n  end\n\n  defp create_country(_) do\n    country = fixture(:country)\n    %{country: country}\n  end\nend\n\nKey Conventions:\n- Uses ExerciseWeb.ConnCase\n- Accepts header set in setup\n- Tests for each HTTP meth\n…(truncated, 2803 more chars)",
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