Notes to myself
This week is the third week of my Flatiron journey and last week we had a code challenge. Students who pass the code challenge get paired up with one of their peers and complete a CLI project together. Those who don’t pass have to complete the project on their own.
This is our chance to use everything we’ve learned in the past two weeks to build something that can run and interact with the user. I was paired up with Faris, a lively guy in our cohort who sits opposite me. After some discussion we decided to build a stock trading application using a real stock price API service.
The process didn’t go very smoothly at first but eventually we solved various issues and completed the project. I enjoyed the pair programming and learned a lot about how to collaborate with others, and know much more about git work flow now.
In this blog, I’m going to focus on some of the problems I came cross when we built this application.
First, though, let me quickly show you the models for the project.
The schema looks like this:
4 Models
│ ├── user.rb
│ ├── portfolio.rb
│ └── position.rb
│ └── stock.rb
User Stories (CRUD)
- As a user, I want to create a account (Create)
- As a user, I want to view my portfolio (Read)
- As a user, I want to view my account (Read)
- As a user, I want to top up and withdraw my balance (Update account balance)
- As a user, I want buy stock (Update position quantity and account balance)
- As a user, I want to sell stock(update position quantity and account balance)
- As a user, I want to delete my account (Destroy account)
Entity relationships
class User
has_one :portfolio
end
class Portfolio
has_many :positions
belongs_to :user
end
class Stock
has_many :positions
end
class Position # This is the join or pivot class for portfolio and stock.
belongs_to :stock
belongs_to :portfolio
end
Database migrations
User table
class CreateUsers < ActiveRecord::Migration[5.2]
def change
create_table :users do |t|
t.string :first_name
t.string :last_name
t.integer :account_balance
t.string :email
t.string :password
t.string :security_answer
end
end
end
Portfolio table
class CreatePortfolios < ActiveRecord::Migration[5.2]
def change
create_table :portfolios do |t|
t.integer :user_id
end
end
end
Position table (join / pivot table for the Portfolio and the Stock table)
class CreatePositions < ActiveRecord::Migration[5.2]
def change
create_table :positions do |t|
t.integer :portfolio_id
t.integer :stock_id
t.integer :quantity, :null => false, :default => 0
end
end
end
Stock table
Note that there is no price column in the Stock table. Instead we used a
public stock price API to fetch live prices at runtime.
class CreateStocks < ActiveRecord::Migration[5.2]
def change
create_table :stocks do |t|
t.string :company_name
t.string :symbol
end
end
end
Some problems and mistakes we encountered
- We wrote a name format checker method which can identify if the name looks like a reasonable name. We used a regex to solve this issue:
def name_format_checker
if /^[a-zA-Z]+(([',. -][a-zA-Z ])?[a-zA-Z]*)*$/.match(@name)
email_getter
else
puts "Oops! Looks like your name format is incorrect. Please try again."
register
end
end
- When I worked on the method for topping up the balance, I kept hitting this error:
in `deposit': undefined method `+' for nil:NilClass (NoMethodError)
The solution was to ensure both parts existed in the user class:
def deposit(money_in)
if money_in == nil
money_in = 0
end
if self.account_balance == nil
self.account_balance = 0
end
self.account_balance += money_in
self.save
end
I also made some changes on my user table, changing the data type for account_balance from integer to decimal, and giving it a default value of 0.0.
class CreateUsers < ActiveRecord::Migration[5.2]
def change
create_table :users do |t|
t.string :first_name
t.string :last_name
t.decimal :account_balance,
:precision => 10,
:scale => 2,
:null => false,
:default => 0.0
t.string :email
t.string :password
t.string :security_answer
end
end
end
- Formatting monetary amounts with two decimal places using
%.2f
Example:
def fmt_balance
balance = 165
'%.2f' % balance
end
#"%.4f" would print 165.0000
#"%.2f" prints 165.00 rounded
The “.2” tells your “print” to print only the first 2 digits after the point.
- top_up method issue: it was accepting a negative number for a top up.
This meant it deducted the amount from your account which of course doesn’t make sense. I solved this by checking if the deposit amount seemed valid before processing it.
Solution code:
def handle_top_up
@user.reload
puts "How much would you like to top up? input a number please!"
deposit_amount = gets.chomp.to_f
if deposit_amount > 0 #check the deposit amount first
@user.deposit(deposit_amount)
puts ""
puts "You have sucessfully topped up $#{'%.2f' % deposit_amount}."
puts "You now have $#{@user.fmt_balance} in your cash account."
puts ""
else
puts "Invalid top-up amount!"
end
end
- Withdraw method issue: when I first created the withdraw method, it let you withdraw as much as you want regardless of your account balance, which of course is a major bug!
To solve it, I had it check if the account balance has enough money first before proceeding.
Example:
def account_valid?(money_out)
money_out <= self.account_balance
end
def withdraw(money_out)
self.account_balance -= money_out
self.save
end
- Issue with the database: the data in memory was not in sync with the database.
I solved this by using the Active Record
reload method in each function that needed the latest state from the database.
You probably noticed that the handle_top_up function uses reload in this
way.
Here is another example:
def view_current_stocks
@user.reload
stocks = Stock.all
100.times do
sleep 0.02
@bar.increment!
end
puts "Stocks in the system:"
puts ""
tp stocks, "company_name", "symbol"
puts ""
input = @prompt.select(
"Which stock are you interested in?",
stocks.map { |stock| stock.symbol }
)
view_single_stock(input)
end
I used a public stock price API to fetch live prices on the real stock market, provided by Alpha Vantage APIs.
I’ll write another blog to share how I set up API for this application.