User Microposts

A Micropost Model

The basic model looks like so:

To create this with a reference to user:

rails g model Micropost content:text user:references
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This will create the following model:

# app/models/micropost.rb
class Micropost < ApplicationRecord
   belongs_to :user
end
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This will also create a migration:

# db/migrate/[timestamp]_create_microposts.rb
class CreateMicroposts < ActiveRecord::Migration[6.0]
  def change
    create_table :microposts do |t|
      t.text :content
      t.references :user, null: false, foreign_key: true

      t.timestamps
    end

    # added by us physically
    add_index :microposts, [:user_id, :created_at]
  end
end
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By including both the user_id and created_at columns as an array, we arrange for Rails to create a multiple key index, which means that Active Record uses both keys at the same time.

User/Micropost associations

Note that because the user can create the microposts, the tests file can be updated to ensure the setup is created idiomatically:

# This code is not idiomatically correct.
@micropost = Micropost.new(content: "Lorem ipsum", user_id: @user.id)

# Correcting that code
@user = users(:michael)
# returns a new post associated with the user
@micropost = @user.microposts.build(content: "Lorem ipsum")
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At this stage, our Micropost and User model looks like so:

class Micropost < ApplicationRecord
  belongs_to :user
  validates :user_id, presence: true
  validates :content, presence: true, length: { maximum: 140 }
end

class User < ApplicationRecord
  has_many :microposts
  .
  .
  .
end
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Micropost Refinements

To ensure testing is correct, we can use :most_recent in our assertion:

require 'test_helper'

class MicropostTest < ActiveSupport::TestCase
  .
  .
  .
  test "order should be most recent first" do
    assert_equal microposts(:most_recent), Micropost.first
  end
end
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Fixtures

To have fixtures set for the testing, we can set test/fixtures/users.yml and test/fixtures/microposts.yml respectively:

name: Michael Example
  email: michael@example.com
  .
  .
  .
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And for the Microposts:

orange:
  content: "I just ate an orange!"
  created_at: <%= 10.minutes.ago %>
  user: michael

tau_manifesto:
  content: "Check out the @tauday site by @mhartl: https://tauday.com"
  created_at: <%= 3.years.ago %>
  user: michael

cat_video:
  content: "Sad cats are sad: https://youtu.be/PKffm2uI4dk"
  created_at: <%= 2.hours.ago %>
  user: michael

most_recent:
  content: "Writing a short test"
  created_at: <%= Time.zone.now %>
  user: michael
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Setting created_at DESC

We can update the model to set the order in the default scope:

class Micropost < ApplicationRecord
  belongs_to :user
  # user stabby lambda
  default_scope -> { order(created_at: :desc) }
  validates :user_id, presence: true
  validates :content, presence: true, length: { maximum: 140 }
end
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Cascade delete microposts if user is deleted

We can also add a refinement to users to tell the User to cascade delete associated Microposts on the removal of a User:

class User < ApplicationRecord
  has_many :microposts, dependent: :destroy
  .
  .
  .
end
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We can add a test like so:

require 'test_helper'

class UserTest < ActiveSupport::TestCase

  def setup
    @user = User.new(name: "Example User", email: "user@example.com",
                     password: "foobar", password_confirmation: "foobar")
  end
  .
  .
  .
  test "associated microposts should be destroyed" do
    @user.save
    @user.microposts.create!(content: "Lorem ipsum")
    assert_difference 'Micropost.count', -1 do
      @user.destroy
    end
  end
end
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