/active-record-review-discussion-questions-houston-web-082718

ActiveRecord Review Discussion

ActiveRecord

Before we learned about ActiveRecord, we were able to call on a class method such as Pet.all which would return a collection of all the pet instances. That method would look like this:

  class Pet
    # ...

    def self.all
      ALL
    end

    # ...
  end

When our class inherits from ActiveRecord::Base, we get the all method (and many more methods) for free.

Discuss with your table the steps involved in ActiveRecord's implementation of the class method all. How is SQL used? What's the return value?

Domain Modeling

With your table discuss how you would model out the relationships between three models Voter, Vote, and Candidate. On which table do the foreign keys belong?

AR Query Methods

Take a look at the following Voter class:

class Voter < ActiveRecord::Base
  has_many :votes
  has_many :candidates, through: :votes
end

By providing the macros has_many :votes and has_many :candidates, through: :votes, ActiveRecord gives the Voter class the instance methods Voter#votes and Voter#candidates. These methods will fire some SQL, grab some rows from the database, and return the appropriate Ruby instances.

Your task is to discuss and write out the SQL statements that will run for each of the following expressions

voter = Voter.create

candidate = Candidate.create

voter.votes

voter.candidates

vote = Vote.create(voter_id: voter.id, candidate_id: candidate.id)

vote = voter.votes.create(candidate: candidate)

vote.voter