Mind your own business View Controller

# ?VC

## **M**ind your own business

## **V**iew

## **C**ontroller

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## **Hi**

### *name -* Peter Saxton

### *@internets -* CrowdHailer

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![](curl.png)

### paywithcurl.com

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![](./explain-mvc-title.png)

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![](./explain-mvc-conversation.png)

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![](./explain-mvc-diff.png)

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![](https://media.giphy.com/media/3o85xwxr06YNoFdSbm/giphy.gif)
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> Phoenix is a web development framework written in Elixir which implements the server-side Model View Controller (MVC) pattern. Many of its components and concepts will seem familiar to those of us with experience in other web frameworks **like Ruby on Rails or Python's Django.**

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![](./getting-started-rails.png)

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![](./martin-fowler-mvc.png)

https://martinfowler.com/eaaDev/uiArchs.html

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## A *little* later

> MVC assumes we are manipulating regular **Smalltalk** objects.

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![](facepalms.jpg)

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## What is **good** software

- Communicates purpose
- Supports evolving requirements
- Can be validated (Predictable/Testable)

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# Strategy > Tactics

*“Strategy without tactics is the slowest route to victory.
Tactics without strategy is the noise before defeat."*

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![](./DDD-books.jpg)

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# Domain Driven Design

### Discover design don't choose it.

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## **Domain**

- A coherent subset of the universe.

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## **Model**

- A useful representation of a domain.

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## **Ubiquitous language**

- Terms used to describe concepts in the domain, and model.

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## **Context**

- The setting in which a ubiquitous language applies.

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# Tactics

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## **Value object**

- Any object whose identity is characterized by its attributes.

- They should be treated as immutable

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```elixir
address = {"create", "duck", "chip"}
```

![](w3w-london.png)
*https://w3w.co/create.duck.chip*

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## **Entity**

- Concept that is defined by it's identity
- Their state can evolve over time

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```elixir
order = %{
  id: 1,
  status: :dispatched,
  address: {"create", "duck", "chip"}
}
```

![](squashed-parcel.jpg)

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## **Ports**

```elixir
defmodule NotificationService do
  @callback alert(User.t(), String.t()) :: {:ok, integer} | {:error, term}
end
```

## and **Adapters**

```elixir
defmodule NotificationService.SMS do
  @behaviour NotificationService

@impl NotificationService
  def alert(user, message) do
    # Send some SMS's
  end
end
```
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# Putting it all together

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![](hexagonal-architecture.png)

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### **Hexagonal** architecture

http://alistair.cockburn.us/Hexagonal+architecture

### **Clean** architecture

https://8thlight.com/blog/uncle-bob/2012/08/13/the-clean-architecture.html

### **Onion** architecture

https://jeffreypalermo.com/2008/07/the-onion-architecture-part-1/

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## **MVC** framework

```
lib/
├── models/
├── views/
├── controllers/
```

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## **MVC** framework

1. Realisation that last project was REST endpoints to update a database.
--

2. Hope that the next one will be the same.
--

**NOTE:** it often is

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```eex
<%= form_for @changeset, user_path(@conn, :create), fn f -> %>
  <label>
    Name: <%= text_input f, :name %>
  </label>

<%= submit "Submit" %>
<% end %>
```
*https://hexdocs.pm/phoenix_html/Phoenix.HTML.Form.html*

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![](hexagonal-architecture.png)

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# DDD lessons

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## All models are **wrong**

> Since all models are wrong the scientist cannot obtain a "correct" one by excessive elaboration. On the contrary following William of Occam he should seek an economical description of natural phenomena. Just as the ability to devise simple but evocative models is the signature of the great scientist so overelaboration and overparameterization is often the mark of mediocrity.

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## Isolate the **model**

- Use ports to obscure infrastructure details
- Start from lib
- Delay descisions about which exciting NoSQL DB is best

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## Functional cohesion

> Functional cohesion is when parts (of a module) are grouped because they all contribute to a single well-defined task

[https://en.wikipedia.org/wiki/Cohesion_(computer_science)](https://en.wikipedia.org/wiki/Cohesion_(computer_science))

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## Tests are **just** one adapter

By having well defined ports into the domain clear testing points are available.

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## Know your **limits**

Understand the bounds of your context

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![](ballast-test.jpg)

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![](flight-attendant.jpg)

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# **?VC** ~~framework~~

- Promote integrity of the model
- Don't call us, we'll call you

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# Raxx

### A Toolkit for web development

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### Web only

```elixir
defmodule MyApp.WWW.Login do
  use Raxx.Server

def handle_request(%{method: :POST, body: body}, %{greeting: greeting}) do
    %{username: username, password: password} = URI.decode_query

if MyApp.authenticate?(username, password) do
      response(:ok)
      |> set_body(greeting)
    else
      response(:forbidden)
      |> set_body("Invalid login details")
    end
  end
end
```
*lib/my_app/www/login.ex*

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### Functional Cohesion

```
my_app/
├── www/
    ├── login.ex/
    ├── login.html.eex/
```
```elixir
defmodule MyApp.Login do
  use Raxx.Server

# Part of Raxx.Kit
  use MyApp.HTMLView, path: "./login.html.eex"

def handle_request(%{method: :GET}, _state) do
    response(:ok)
    |> render(%{})
  end

def handle_request(%{method: :POST, body: body}, _state) do
  # ...
end
```

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### Start on demand

```elixir
defmodule MyApp.WWW do
  use Ace.HTTP.Service, cleartext: true
end
```
*lib/my_app/www.ex*

```elixir
children = [
  {MyApp.WWW, [%{greeting: "Hello"}, [port: 80]]}
  {MyApp.Admin, [%{}, [port: 4000]]}
]
```
*lib/my_app/application.ex*

```elixir
setup do
  {:ok, service} = MyApp.WWW.start_link(TEST, port: 0)
  # etc
end
```
*test/my_app/www_test.ex*

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# Questions?

*@CrowdHailer*