eight.sql

SELECT STUDENTS.name, case when PAYMENTS.amount > 0 then 'true' else 'false' end AS have_paid, 
FROM students WHERE MONTH(PAYMENTS.created_at) = 2

five.rb

class StringValidator
  attr_accessor :string
  
  def initialize(string)    
    puts valid_string?(string)
  end
  
  def valid_string?(string)
    return false unless string.length >= 8
    return false unless string =~ /[0-9]/
    return false unless string =~ /[[:upper:]]/
    return false unless string =~ /[[:lower:]]/
    true
  end
end

result_false = StringValidator.new('hello123')
puts result_false #false


result_true = StringValidator.new('hello123Hi')
puts result_true #true

four.rb

class SimpleMath
  def initialize(number1, number2)
    @number1 = number1
    @number2 = number2  
  end 
  
  def add
    puts @number1 + @number2
  end
  
  def subtract
    puts @number1 - @number2
  end

  def multiply
    puts @number1 * @number2
  end
  
  def divide
    puts @number1 / @number2
  end
end

# example use
# m = SimpleMath.new(4,3)
# m.add
# m.subtract
# m.multiply
# m.divide

nine.txt

I would simply run either: tail -f log production.log

OR

try to run the rails console to see if it booted up on the server

one.css

p {
  color: blue;
}

seven.sql

SELECT registered_at, COUNT(DISTINCT id) FROM students GROUP BY registered_at

six.rb

class Person
  attr_accessor :title, :first_name, :middle_name, :last_name
   
  def initialize(first_name, middle_name, last_name, title)
    return create_person(first_name, middle_name, last_name, title)
  end
   
  private 
   
  def get_title(title)
    if ['Dr.', 'Mr.', 'Mrs.', 'Ms.'].include? title
      return title
    end  
  end
    
  def create_person(first_name, middle_name, last_name, title)
     person = {  first_name: first_name, middle_name: middle_name, last_name: last_name, title: get_title(title)  }
  end
end

person = Person.new('Robert', 'William', 'Barker', 'Mr.')
puts person

ten.txt

Since a 500 error is occurring, I can narrow down that the error is coming from somewhere on the server side of my application. Hopefully my application is organized enough to where I can narrow the 5xx error and figure out what exactly might be happening.

1) First thing is I would check the applications log file to see if there were any specific errors that the 500 was pulling. This would probably give me my best chance of figuring out what is wrong. But if not I would move onto step 2. 
2) I would check out the code/api endpoint that needs diagnosed, and I would evaluate if any dependencies might be effecting the response. I would also make sure logging is turned on in production to make sure that errors are being logged.
3) After evaluating and checking out the code to make sure it looks good, I would test the endpoint in a development environment to see if I could replicate getting the 500 error.
3) If I couldn't get the 500 error, I would perhaps see if I could refactor any of the endpoint to potentially fix the problem. At this point
4) Here I would start to think it was a connection issue, where too many connections might be occuring at one time on the endpoint. I would try and increase allowed connections and also see if I could decrease any external connections to my database so I can make sure that data gets passed through without 500 error.
5) At this point, if my application had an .htaccess file, I would remove it to make sure that this is not the problem (which most likely it wouldn't be because my API for the most part is working).

three.js

$.ajax({
  url: '/api/v1/students.json',
  dataType: 'json',
  success: function(data) {
    $('#students').append(data.students);
  },
  error: function (request, error) {
    console.log(error);
  }
}); 

// or render partial through js.erb where my endpoint responds to format.js

$.ajax({
  url: '/api/v1/students.json',
  dataType: 'json',
  success: function(data) {
    $('#students').html('<%= @students_variable %>');
  },
  error: function (request, error) {
    console.log(error);
  }
});

two.js

Object.keys(people).forEach(function (key) { 
  console.log(people[key].first_name);
});