Basic ActiveRecord Methods

Today I am working on some basic db calls to tough on some of those simple concepts that feels like I learned ages ago. Here is the quiz and my answers below:

ActiveRecord Lookups Quiz

Without looking for help online write the following queries:

1. Find an author with an id of 9.

Answer: Author.find(9)
Why: Using the Find method only takes id numbers as inputs and returns a single value based on that input.

2. Find all authors with a last_name of Brown.

Answer: Author.find_by(last_name: 'Brown')
Why: find_by searches by attributes of the model that it is called on and returns the first instances where the condition is met.

3. Find the first author with a last_name of Brown.

Answer: Author.find_by(last_name: 'Brown)
Why: refer back to question 2

4. Find all articles created in the last 5 days.

Answer: Article.where("created_at >= ?", 5.days.ago)
Why: Here I decided to use sql paired with AR (ActiveRecord) to simplify my code. Using .where was the best choice in my opinion because I am searching the whole database to see is my condition (article being created in the last 5 days) has been met. If there haven't been any articles created then this method should return an empty array.

Using only one call to the database:

5. Find all users with a last_name of 'Brown' and return the first user with a first_name of 'Nancy'.

Answer: User.where(last_name: 'Brown').find_by(first_name: 'Nancy')
Why: .where searches the db for users where the last_name == 'Brown'. This returns an array, on that array I then am using find_by to find the first instance where the first_name is 'Nancy'.

6. Find all articles created in the last 5 days. Display the article title and author's last_name for each article.

• Article.where(created_at: 5.days.ago..Time.now) .includes(:author) .select("title, users.last_name as author_last_name") .map { |article| [article.title, article.author_last_name] }

Bonus Round

7. What's the danger of using update_attribute vs update_attributes?

Answer and Why: 'update_attribute' changes a singular attribute WITHOUT checking against validations and callbacks. While 'update_attributes' changes multiple the attributes and checks the validations and callbacks. So the danger would be that using update_attribute' you may accidentally save an attribute that is an invalid value.

8. Imagine we are creating and loading users based on data received from an external service (attributes in this example).

Refactor the method below to use .first_or_initialize and .tap:

  def self.find_or_create_from_external_service(attributes = {})
    user = User.find_by_login(attributes[:login])
    if user.nil?
      user = User.create(login: attributes[:login], email: attributes[:email])
    end

    user
  end

refactor:

  def self.find_or_create_from_external_service(attributes = {})
    User.where(login: attributes[:login]).first_or_initialize.tap do |user|
      user.update(email: attributes[:email]) if user.new_record?
      user.save
    end
  end