### app/models/user.erb
```ruby
class User < ActiveRecord::Base

  # All of the fields listed here are required
  validates_presence_of :email, :avatar_url, :username, :password

  # All of these fields must be unique (i.e. can't register the same email twice)
  validates_uniqueness_of :email, :username

 end
```

### app/views/register.erb
```html
<form method="post" action="/register">

    <label for="email">Email:</label>
    <input type="email" name="email" id="email" required>

    <br><br>

    <label for="username">Username:</label>
    <input type="text" name="username" id="username" required>

    <br><br>

    <label for="avatar_url">Avatar URL:</label>
    <input type="url" name="avatar_url" id="avatar_url" required>

    <br><br>

    <label for="password">Password:</label>
    <input type="password" name="password" id="password" required>

    <br><br>

    <input type="submit">

</form>
```

### app/actions.rb
```ruby
get '/register' do
  erb :register
end

post '/register' do
  # Get the values the user submitted in the form
  email = params[:email]
  username = params[:username]
  avatar_url = params[:avatar_url]
  password = params[:password]

  # Create a new instance of the user class
  @user = User.new(email: email, username: username, avatar_url: avatar_url, password: password)

  # Try saving the user to the database
  # Remember that .save automatically runs validations and returns true or false
  if @user.save
    # Saving worked, so render a success page!
    erb :registration_success
  else
    # Saving did not work, show a failure page
    erb :registration_failure
  end
end
```

### app/views/registration_success.erb
```html
Yay! It worked!
```

### app/views/registration_failure.erb
```html
No dice, try again.
```