Session: bubbly-baking-prism-subagent-ac41f0b — 2026-02-13

Project: salary-crud · Branch: main · Mode: ` · **Model:**claude-haiku-4-5-20251001`

Stats: 1 user messages, 27 tool calls, tools used: Bash, Read.

Conversation

Turn 1 — User

I need to understand the existing code patterns in this Phoenix application to ensure the implementation plan follows the same conventions.

Investigate: 1. How are the existing resources (Country, Currency) structured? Look at: - Schema definitions (lib/be_exercise/countries/*.ex) - Context modules - Controllers and JSON views (lib/be_exercise_web/controllers/) - Test patterns

2. What's the current router configuration?

3. How is the seeds.exs file currently structured?

4. What data files exist in priv/data/?

This will help validate the implementation plan's assumptions about code structure and conventions.

Turn 1 — Assistant

I'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.

Tools used:

• Bash: find /Users/USER/workspace/playground/employee-salary-crud -type f -name "*.ex" -o -name "*.exs" | head -30

Tool results:

→ result (ok): /Users/USER/workspace/playground/employee-salary-crud/mix.exs /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/country_controller_test.exs /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/error_json_test.exs /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/currency_controller_test.exs /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise/countries_test.exs /Users/USE …(truncated, 2532 more chars)

Let me continue exploring the structure more thoroughly.

Tools used:

• Bash: ls -la /Users/USER/workspace/playground/employee-salary-crud/lib/

Tool results:

→ result (ok): drwxr-xr-x clertonra staff 192 B Fri Feb 13 16:13:08 2026 . drwxr-xr-x clertonra staff 512 B Fri Feb 13 16:14:42 2026 .. drwxr-xr-x clertonra staff 224 B Fri Feb 13 16:13:08 2026 be_exercise .rw-r--r-- clertonra staff 253 B Fri Feb 13 16:13:08 2026 be_exercise.ex drwxr-xr-x clertonra staff 224 B Fri Feb 13 16:13:08 2026 be_exercise_web .rw-r--r-- clertonra staff 2.2 KB Fri Feb 13 16:13:08 2026 be_exercise_web.ex

Tools used:

• Bash: find /Users/USER/workspace/playground/employee-salary-crud/lib -type f -name "*.ex" | sort

Tool results:

→ result (ok): /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web.ex /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/changeset_json.ex /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_controller.ex /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_json.ex /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/currency_controller.ex

…(truncated, 1359 more chars)

Now let me explore the specific files mentioned in your requirements:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/countries/country.ex

Tool results:

→ result (ok): 1→defmodule Exercise.Countries.Country do 2→ use Ecto.Schema 3→ import Ecto.Changeset 4→ 5→ schema "countries" do 6→ field :code, :string 7→ field :name, :string 8→ 9→ timestamps() 10→ end 11→ 12→ @doc false 13→ def changeset(country, attrs) do 14→ country 15→ |> cast(attrs, [:name, :code]) 16→ |> validate_required([:name, :code]) 17→ |> unique_constraint(:name) 18→ |> unique_constraint(:cod …(truncated, 373 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/countries/currency.ex

Tool results:

→ result (ok): 1→defmodule Exercise.Countries.Currency do 2→ use Ecto.Schema 3→ import Ecto.Changeset 4→ 5→ schema "currencies" do 6→ field :code, :string 7→ field :name, :string 8→ field :symbol, :string 9→ 10→ timestamps() 11→ end 12→ 13→ @doc false 14→ def changeset(currency, attrs) do 15→ currency 16→ |> cast(attrs, [:code, :name, :symbol]) 17→ |> validate_required([:code, :name, :symbol]) 18→ |> uniqu …(truncated, 429 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/countries.ex

Tool results:

→ result (ok): 1→defmodule Exercise.Countries do 2→ @moduledoc """ 3→ The Countries context. 4→ """ 5→ 6→ import Ecto.Query, warn: false 7→ alias Exercise.Repo 8→ 9→ alias Exercise.Countries.Currency 10→ 11→ @doc """ 12→ Returns the list of currencies. 13→ 14→ ## Examples 15→ 16→ iex> list_currencies() 17→ [%Currency{}, ...] 18→ 19→ """ 20→ def list_currencies do 21→ Repo.all(Currency) 22→ end

…(truncated, 5397 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/router.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.Router do 2→ use ExerciseWeb, :router 3→ 4→ pipeline :api do 5→ plug :accepts, ["json"] 6→ end 7→ 8→ scope "/api", ExerciseWeb do 9→ pipe_through :api 10→ 11→ resources "/currencies", CurrencyController 12→ resources "/countries", CountryController 13→ end 14→ 15→ # Enables LiveDashboard only for development 16→ # 17→ # If you want to use the LiveDashboard in production, you should …(truncated, 970 more chars)

Now let me examine the controllers and JSON views:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_controller.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.CountryController do 2→ use ExerciseWeb, :controller 3→ 4→ alias Exercise.Countries 5→ alias Exercise.Countries.Country 6→ 7→ action_fallback ExerciseWeb.FallbackController 8→ 9→ def index(conn, _params) do 10→ countries = Countries.list_countries() 11→ render(conn, :index, countries: countries) 12→ end 13→ 14→ def create(conn, %{"country" => country_params}) do 15→ with {:ok, %Country{} = cou …(truncated, 1360 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/country_json.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.CountryJSON do 2→ alias Exercise.Countries.Country 3→ 4→ @doc """ 5→ Renders a list of countries. 6→ """ 7→ def index(%{countries: countries}) do 8→ %{data: for(country <- countries, do: data(country))} 9→ end 10→ 11→ @doc """ 12→ Renders a single country. 13→ """ 14→ def show(%{country: country}) do 15→ %{data: data(country)} 16→ end 17→ 18→ defp data(%Country{} = country) do

…(truncated, 489 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/currency_controller.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.CurrencyController do 2→ use ExerciseWeb, :controller 3→ 4→ alias Exercise.Countries 5→ alias Exercise.Countries.Currency 6→ 7→ action_fallback ExerciseWeb.FallbackController 8→ 9→ def index(conn, _params) do 10→ currencies = Countries.list_currencies() 11→ render(conn, :index, currencies: currencies) 12→ end 13→ 14→ def create(conn, %{"currency" => currency_params}) do 15→ with {:ok, %Currenc …(truncated, 1396 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/currency_json.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.CurrencyJSON do 2→ alias Exercise.Countries.Currency 3→ 4→ @doc """ 5→ Renders a list of currencies. 6→ """ 7→ def index(%{currencies: currencies}) do 8→ %{data: for(currency <- currencies, do: data(currency))} 9→ end 10→ 11→ @doc """ 12→ Renders a single currency. 13→ """ 14→ def show(%{currency: currency}) do 15→ %{data: data(currency)} 16→ end 17→ 18→ defp data(%Currency{} = c …(truncated, 544 more chars)

Now let me check the test patterns and migration files:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise/countries_test.exs

Tool results:

→ result (ok): 1→defmodule Exercise.CountriesTest do 2→ use Exercise.DataCase 3→ 4→ alias Exercise.Countries 5→ 6→ describe "currencies" do 7→ alias Exercise.Countries.Currency 8→ 9→ @valid_attrs %{code: "some code", name: "some name", symbol: "some symbol"} 10→ @update_attrs %{ 11→ code: "some updated code", 12→ name: "some updated name", 13→ symbol: "some updated symbol" 14→ } 15→ @invalid_attrs %{code: nil, name …(truncated, 5358 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/country_controller_test.exs

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.CountryControllerTest do 2→ use ExerciseWeb.ConnCase 3→ 4→ alias Exercise.Countries 5→ alias Exercise.Countries.Country 6→ 7→ @create_attrs %{ 8→ code: "some code", 9→ name: "some name" 10→ } 11→ @update_attrs %{ 12→ code: "some updated code", 13→ name: "some updated name" 14→ } 15→ @invalid_attrs %{code: nil, name: nil} 16→ 17→ def fixture(:country) do 18→ {:ok, country} = …(truncated, 3191 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/priv/repo/migrations/20210720101412_create_countries.exs

Tool results:

→ result (ok): 1→defmodule Exercise.Repo.Migrations.CreateCountries do 2→ use Ecto.Migration 3→ 4→ def change do 5→ create table(:countries) do 6→ add :name, :string 7→ add :code, :string 8→ 9→ timestamps() 10→ end 11→ 12→ create unique_index(:countries, [:name]) 13→ create unique_index(:countries, [:code]) 14→ end 15→end 16→

<system-reminder> Whenever you read a file, you should consider whether it would be cons …(truncated, 249 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/priv/repo/migrations/20210720100728_create_currencies.exs

Tool results:

→ result (ok): 1→defmodule Exercise.Repo.Migrations.CreateCurrencies do 2→ use Ecto.Migration 3→ 4→ def change do 5→ create table(:currencies) do 6→ add :code, :string 7→ add :name, :string 8→ add :symbol, :string 9→ 10→ timestamps() 11→ end 12→ end 13→end 14→

<system-reminder> Whenever 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 …(truncated, 173 more chars)

Now let me check the seeds file and data directory:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/priv/repo/seeds.exs

Tool results:

→ result (ok): 1→# Script for populating the database. You can run it as: 2→# 3→# mix run priv/repo/seeds.exs 4→# 5→# Inside the script, you can read and write to any of your 6→# repositories directly: 7→# 8→# Exercise.Repo.insert!(%Exercise.SomeSchema{}) 9→# 10→# We recommend using the bang functions (insert!, update! 11→# and so on) as they will fail if something goes wrong. 12→# 13→# The code below demonstrates initial data insertion for cu …(truncated, 2105 more chars)

Tools used:

• Bash: ls -la /Users/USER/workspace/playground/employee-salary-crud/priv/data/ 2>/dev/null || echo "Directory does not exist"

Tool results:

→ result (ok): drwxr-xr-x clertonra staff 160 B Fri Feb 13 16:13:08 2026 . drwxr-xr-x clertonra staff 160 B Fri Feb 13 16:13:08 2026 .. .rw-r--r-- clertonra staff 1.4 KB Fri Feb 13 16:13:08 2026 first_names.txt .rw-r--r-- clertonra staff 6.6 KB Fri Feb 13 16:13:08 2026 job_titles.txt .rw-r--r-- clertonra staff 4.3 KB Fri Feb 13 16:13:08 2026 last_names.txt

Excellent! Let me check those data files and also look at some additional controller/helper files:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/priv/data/first_names.txt (1–30)

Tool results:

→ result (ok): 1→Ruth 2→Nicholas 3→Teresa 4→Frances 5→Sophia 6→Diane 7→Gabriel 8→Logan 9→Donna 10→Juan 11→Joshua 12→Jean 13→Dennis 14→Daniel 15→Dylan 16→Alan 17→Lauren 18→Karen 19→Aaron 20→Hannah 21→Barbara 22→Elizabeth 23→Andrea 24→Marilyn 25→Jordan 26→Jacob 27→Andrew 28→Brandon 29→Martha 30→Carolyn

<system-reminder> Whenever you read a file, you should consider whether it would be cons …(truncated, 249 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/fallback_controller.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.FallbackController do 2→ @moduledoc """ 3→ Translates controller action results into valid Plug.Conn responses. 4→ 5→ See Phoenix.Controller.action_fallback/1 for more details. 6→ """ 7→ use ExerciseWeb, :controller 8→ 9→ # This clause handles errors returned by Ecto's insert/update/delete. 10→ def call(conn, {:error, %Ecto.Changeset{} = changeset}) do 11→ conn 12→ |> put_status(:unprocessable_entity)

…(truncated, 775 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/changeset_json.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.ChangesetJSON do 2→ use ExerciseWeb, :view 3→ 4→ @doc """ 5→ Traverses and translates changeset errors. 6→ 7→ See Ecto.Changeset.traverse_errors/2 and 8→ ExerciseWeb.ErrorHelpers.translate_error/1 for more details. 9→ """ 10→ def translate_errors(changeset) do 11→ Ecto.Changeset.traverse_errors(changeset, &translate_error/1) 12→ end 13→ 14→ def error(%{changeset: changeset}) do 15→ # When e …(truncated, 520 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/error_json.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.ErrorJSON do 2→ @moduledoc """ 3→ This module is invoked by your endpoint in case of errors on JSON requests. 4→ 5→ See config/config.exs. 6→ """ 7→ 8→ # If you want to customize a particular status code, 9→ # you may add your own clauses, such as: 10→ # 11→ # def render("500.json", _assigns) do 12→ # %{errors: %{detail: "Internal Server Error"}} 13→ # end 14→ 15→ # By default, Phoenix returns th …(truncated, 612 more chars)

Let me also check a couple of controller tests and the top-level context module:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/test/be_exercise_web/controllers/currency_controller_test.exs

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.CurrencyControllerTest do 2→ use ExerciseWeb.ConnCase 3→ 4→ alias Exercise.Countries 5→ alias Exercise.Countries.Currency 6→ 7→ @create_attrs %{ 8→ code: "some code", 9→ name: "some name", 10→ symbol: "some symbol" 11→ } 12→ @update_attrs %{ 13→ code: "some updated code", 14→ name: "some updated name", 15→ symbol: "some updated symbol" 16→ } 17→ @invalid_attrs %{code: nil, na …(truncated, 3469 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise.ex

Tool results:

→ result (ok): 1→defmodule Exercise do 2→ @moduledoc """ 3→ Exercise keeps the contexts that define your domain 4→ and business logic. 5→ 6→ Contexts are also responsible for managing your data, regardless 7→ if it comes from the database, an external API or others. 8→ """ 9→end 10→

<system-reminder> Whenever 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 …(truncated, 157 more chars)

Perfect! Now let me check the application structure and look at the service pattern used:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/services/currency_converter.ex

Tool results:

→ result (ok): 1→defmodule Exercise.Services.CurrencyConverter do 2→ @moduledoc """ 3→ Module implementing the currency conversion service 4→ 5→ Note: The current implementation will not contact any external service 6→ and will use fixed conversion rates that will most likely not be the correct ones. 7→ """ 8→ 9→ def convert(from, to, amount) do 10→ rates()["#{to}#{from}"] * amount 11→ end 12→ 13→ defp rates do 14→ %{ 15→ "EURGB …(truncated, 2252 more chars)

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise/application.ex

Tool results:

→ result (ok): 1→defmodule Exercise.Application do 2→ # See https://hexdocs.pm/elixir/Application.html 3→ # for more information on OTP Applications 4→ @moduledoc false 5→ 6→ use Application 7→ 8→ def start(_type, _args) do 9→ children = [ 10→ # Start the Ecto repository 11→ Exercise.Repo, 12→ # Start the Telemetry supervisor 13→ ExerciseWeb.Telemetry, 14→ # Start the PubSub system 15→ {Phoenix.PubSub, name: E …(truncated, 1098 more chars)

Perfect! Now let me check error handling patterns and verify the mix.exs to understand the project structure:

Tools used:

• Read: /Users/USER/workspace/playground/employee-salary-crud/lib/be_exercise_web/controllers/error_helpers.ex

Tool results:

→ result (ok): 1→defmodule ExerciseWeb.ErrorHelpers do 2→ @moduledoc """ 3→ Conveniences for translating and building error messages. 4→ """ 5→ 6→ @doc """ 7→ Translates an error message using gettext. 8→ """ 9→ def translate_error({msg, opts}) do 10→ # When using gettext, we typically pass the strings we want 11→ # to translate as a static argument: 12→ # 13→ # # Translate "is invalid" in the "errors" domain 14→ # dgette …(truncated, 1285 more chars)

Tools used:

• Bash: head -50 /Users/USER/workspace/playground/employee-salary-crud/mix.exs

Tool results:

→ result (ok): defmodule Exercise.MixProject do use Mix.Project

def project do [ app: :be_exercise, version: "0.1.0", elixir: "~> 1.18", elixirc_paths: elixirc_paths(Mix.env()), compilers: Mix.compilers(), start_permanent: Mix.env() == :prod, aliases: aliases(), deps: deps(), listeners: [Phoenix.CodeReloader] ] end

# Configuration for the OTP application. # # Type mix help compile.app for more information. def application do [

…(truncated, 786 more chars)

Excellent! Now I have comprehensive understanding of the codebase. Let me compile my findings into a detailed report.

Code Pattern Analysis - Phoenix Application Investigation

Based on my thorough examination of the existing codebase, here's a comprehensive analysis of the patterns and conventions used in this Phoenix application:

1. Project Structure & Naming Conventions

Module Namespacing: - Top-level app module: Exercise (defined in lib/be_exercise.ex) - Web module: ExerciseWeb (defined in lib/be_exercise_web.ex) - All app files use be_exercise prefix in directory names - All web files use be_exercise_web prefix in directory names

Notable: The module names (Exercise, ExerciseWeb) don't match the directory prefixes (be_exercise, be_exercise_web). This is important for the Employee module naming.

2. Schema Definitions

Pattern Found (lib/be_exercise/countries/country.ex and currency.ex):

defmodule Exercise.Countries.Country do
  use Ecto.Schema
  import Ecto.Changeset

  schema "countries" do
    field :code, :string
    field :name, :string
    timestamps()
  end

  @doc false
  def changeset(entity, attrs) do
    entity
    |> cast(attrs, [:name, :code])
    |> validate_required([:name, :code])
    |> unique_constraint(:name)
    |> unique_constraint(:code)
  end
end

Key Conventions: - Schemas nested under context modules in subdirectories (countries/country.ex) - All fields are typed (typically :string) - Timestamps always included - Changesets implement validation + uniqueness constraints - @doc false on changesets (private docs)

3. Context Module Pattern

Structure (lib/be_exercise/countries.ex): - Single context file for related resources (Countries context handles both Country and Currency) - Functions follow naming pattern: list_<resource>, get_<resource>!, create_<resource>, update_<resource>, delete_<resource>, change_<resource> - All public functions have @doc with examples (iex format) - Uses Ecto.Query for custom queries with where clauses - Direct Repo.all, Repo.get!, Repo.insert, Repo.update, Repo.delete calls

Functions provided: - List operations (list_currencies, list_countries) - Get by ID (get_currency!, get_country!) - Get by attribute (get_currency_by_code!) - CRUD operations (create_*, update_*, delete_*) - Change tracking (change_currency, change_country)

4. Controller Pattern

Structure (lib/be_exercise_web/controllers/country_controller.ex):

defmodule ExerciseWeb.CountryController do
  use ExerciseWeb, :controller

  alias Exercise.Countries
  alias Exercise.Countries.Country

  action_fallback ExerciseWeb.FallbackController

  # index, create, show, update, delete actions
end

Key Conventions: - use ExerciseWeb, :controller macro - Aliases for context and schema - action_fallback decorator for error handling - Standard RESTful actions: index, create, show, update, delete - Use with pattern for error handling - HTTP status codes: :created (201) for create, :no_content (204) for delete - Response headers set with put_resp_header for create (location) - Parameters wrapped in resource name: %{"country" => country_params}

5. JSON View/Renderer Pattern

Structure (lib/be_exercise_web/controllers/country_json.ex):

defmodule ExerciseWeb.CountryJSON do
  alias Exercise.Countries.Country

  def index(%{countries: countries}) do
    %{data: for(country <- countries, do: data(country))}
  end

  def show(%{country: country}) do
    %{data: data(country)}
  end

  defp data(%Country{} = country) do
    %{
      id: country.id,
      name: country.name,
      code: country.code
    }
  end
end

Key Conventions: - Module named <Resource>JSON - Functions match controller actions: index, show - All responses wrapped in %{data: ...} structure - Private data/1 function for individual resource rendering - Only specific fields exposed (ID, name, code, etc.) - no timestamps or auto-fields

6. Router Configuration

Pattern (lib/be_exercise_web/router.ex):

defmodule ExerciseWeb.Router do
  use ExerciseWeb, :router

  pipeline :api do
    plug :accepts, ["json"]
  end

  scope "/api", ExerciseWeb do
    pipe_through :api

    resources "/currencies", CurrencyController
    resources "/countries", CountryController
  end
end

Key Conventions: - API routes nested under /api scope - Uses resources macro for RESTful routing - Controllers in scope automatically use ExerciseWeb module prefix - Single api pipeline for JSON requests

7. Error Handling & Fallback

FallbackController (lib/be_exercise_web/controllers/fallback_controller.ex):

def call(conn, {:error, %Ecto.Changeset{} = changeset}) do
  conn
  |> put_status(:unprocessable_entity)
  |> put_view(json: ExerciseWeb.ChangesetJSON)
  |> render("error.json", changeset: changeset)
end

ChangesetJSON (lib/be_exercise_web/controllers/changeset_json.ex):

def error(%{changeset: changeset}) do
  %{errors: translate_errors(changeset)}
end

Key Conventions: - :unprocessable_entity (422) for validation errors - Errors wrapped in %{errors: {...}} structure - Uses translate_error/1 from ErrorHelpers - Gettext integration for i18n

8. Migration Pattern

Structure (priv/repo/migrations/20210720101412_create_countries.exs):

defmodule Exercise.Repo.Migrations.CreateCountries do
  use Ecto.Migration

  def change do
    create table(:countries) do
      add :name, :string
      add :code, :string
      timestamps()
    end

    create unique_index(:countries, [:name])
    create unique_index(:countries, [:code])
  end
end

Key Conventions: - Module name matches timestamp prefix: YYYYMMDDhhmmss_action - Uses Ecto.Migration - Unique indices created directly in migration (matching schema constraints) - timestamps() automatically added - Field order: code first, then name (for currencies)

9. Test Pattern - Context Tests

Structure (test/be_exercise/countries_test.exs):

defmodule Exercise.CountriesTest do
  use Exercise.DataCase

  describe "currencies" do
    @valid_attrs %{code: "some code", name: "some name", symbol: "some symbol"}
    @update_attrs %{...}
    @invalid_attrs %{code: nil, name: nil, symbol: nil}

    def currency_fixture(attrs \\ %{}) do
      {:ok, currency} = Countries.create_currency(attrs |> Enum.into(@valid_attrs))
      currency
    end

    test "list_currencies/0 returns all currencies" do
      # test body
    end
  end
end

Key Conventions: - Uses Exercise.DataCase (not ExerciseWeb.ConnCase for context tests) - Module attributes for valid/update/invalid data - Fixture functions for creating test data - describe blocks for grouping related tests - Tests for each context function: list, get, create, update, delete, change

10. Test Pattern - Controller Tests

Structure (test/be_exercise_web/controllers/country_controller_test.exs):

defmodule ExerciseWeb.CountryControllerTest do
  use ExerciseWeb.ConnCase

  setup %{conn: conn} do
    {:ok, conn: put_req_header(conn, "accept", "application/json")}
  end

  describe "index" do
    test "lists all countries", %{conn: conn} do
      conn = get(conn, Routes.country_path(conn, :index))
      assert json_response(conn, 200)["data"] == []
    end
  end

  describe "create country" do
    test "renders country when data is valid", %{conn: conn} do
      conn = post(conn, Routes.country_path(conn, :create), country: @create_attrs)
      assert %{"id" => id} = json_response(conn, 201)["data"]
    end
  end

  defp create_country(_) do
    country = fixture(:country)
    %{country: country}
  end
end

Key Conventions: - Uses ExerciseWeb.ConnCase - Accepts header set in setup - Tests for each HTTP meth …(truncated, 2803 more chars)