Black Thursday Iteration 3 - Item Sales

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We’ve got a good foundation, now it’s time to actually track the sale of items. There are three new data files to mix into the system, so for this iteration we’ll focus primarily on DAL with just a bit of Business Intelligence.

Parts to iteration 3: Data Access Layer Business Intelligence

Data Access Layer

InvoiceItem

InvoiceItem objects are how invoices are connected to items. A single InvoiceItem connects a single Item with a single Invoice.

The InvoiceItem has the following data accessible:

• id - returns the integer id
• item_id - returns the item id
• invoice_id - returns the invoice id
• quantity - returns the quantity
• unit_price - returns the unit_price
• created_at - returns a Time instance for the date the invoice item was first created
• updated_at - returns a Time instance for the date the invoice item was last modified

It also offers the following method:

• unit_price_to_dollars - returns the price of the invoice item in dollars formatted as a Float

We create an instance like this:

ii = InvoiceItem.new({
  :id => 6,
  :item_id => 7,
  :invoice_id => 8,
  :quantity => 1,
  :unit_price => BigDecimal(10.99, 4),
  :created_at => Time.now,
  :updated_at => Time.now
})
# => <InvoiceItem...>

ii.unit_price_to_dollars
# => 23.48

InvoiceItemRepository

The InvoiceItemRepository is responsible for holding and searching our InvoiceItem instances. It offers the following methods:

• all - returns an array of all known InvoiceItem instances
• find_by_id - returns either nil or an instance of InvoiceItem with a matching ID
• find_all_by_item_id - returns either [] or one or more matches which have a matching item ID
• find_all_by_invoice_id - returns either [] or one or more matches which have a matching invoice ID
• create(attributes) - create a new InvoiceItem instance with the provided attributes. The new InvoiceItem’s id should be the current highest InvoiceItem id plus 1.
• update(id, attribute) - update the InvoiceItem instance with the corresponding id with the provided attributes. Only the invoice_item’s quantity and unit_price can be updated. This method will also change the invoice_item’s updated_at attribute to the current time.
• delete(id) - delete the InvoiceItem instance with the corresponding id

The data can be found in data/invoice_items.csv so the instance is created and used like this:

sales_engine = SalesEngine.from_csv(:invoice_items => "./data/invoice_items.csv")
invoice_item = sales_engine.invoice_items.find_by_id(6)
# => <InvoiceItem...>

Transaction

Transactions are billing records for an invoice. An invoice can have multiple transactions, but should have at most one that is successful.

The transaction has the following data accessible:

• id - returns the integer id
• invoice_id - returns the invoice id
• credit_card_number - returns the credit card number
• credit_card_expiration_date - returns the credit card expiration date
• result - the transaction result
• created_at - returns a Time instance for the date the transaction was first created
• updated_at - returns a Time instance for the date the transaction was last modified

We create an instance like this:

t = Transaction.new({
  :id => 6,
  :invoice_id => 8,
  :credit_card_number => "4242424242424242",
  :credit_card_expiration_date => "0220",
  :result => "success",
  :created_at => Time.now,
  :updated_at => Time.now
})

TransactionRepository

The TransactionRepository is responsible for holding and searching through our Transaction instances. It offers the following methods:

• all - returns an array of all known Transaction instances
• find_by_id - returns either nil or an instance of Transaction with a matching ID
• find_all_by_invoice_id - returns either [] or one or more matches which have a matching invoice ID
• find_all_by_credit_card_number - returns either [] or one or more matches which have a matching credit card number
• find_all_by_result - returns either [] or one or more matches which have a matching status
• create(attributes) - create a new Transaction instance with the provided attributes. The new Transaction’s id should be the current highest Transaction id plus 1.
• update(id, attribute) - update the Transaction instance with the corresponding id with the provided attributes. Only the transaction’s credit_card_number, credit_card_expiration_date, and result can be updated. This method will also change the transaction’s updated_at attribute to the current time.
• delete(id) - delete the Transaction instance with the corresponding id

The data can be found in data/transactions.csv. An instance is created and used like this:

sales_engine = SalesEngine.from_csv(:transactions => "./data/transactions.csv")
transaction = sales_engine.transactions.find_by_id(6)
# => <Transaction... @id=6>

Customer

A Customer represents a person who has made one or more purchases in our system.

The customer instance has the following data accessible:

• id - returns the integer id
• first_name - returns the first name
• last_name - returns the last name
• created_at - returns a Time instance for the date the customer was first created
• updated_at - returns a Time instance for the date the customer was last modified

We create an instance like this:

c = Customer.new({
  :id => 6,
  :first_name => "Joan",
  :last_name => "Clarke",
  :created_at => Time.now,
  :updated_at => Time.now
})
# => <Customer...>

CustomerRepository

The CustomerRepository is responsible for holding and searching our Customer instances. It offers the following methods:

• all - returns an array of all known Customer instances
• find_by_id - returns either nil or an instance of Customer with a matching ID
• find_all_by_first_name - returns either [] or one or more matches which have a first name matching the substring fragment supplied
• find_all_by_last_name - returns either [] or one or more matches which have a last name matching the substring fragment supplied
• create(attributes) - create a new Customer instance with the provided attributes. The new Customer’s id should be the current highest Customer id plus 1.
• update(id, attribute) - update the Customer instance with the corresponding id with the provided attributes. Only the customer’s first_name and last_name can be updated. This method will also change the customer’s updated_at attribute to the current time.
• delete(id) - delete the Customer instance with the corresponding id

The data can be found in data/customers.csv so the instance is created and used like this:

sales_engine = SalesEngine.from_csv(:customers => "./data/customers.csv")
customer = sales_engine.customers.find_by_id(6)
# => <Customer... @id=6>

Business Intelligence

Assuming we have a SalesEngine instance called sales_engine, let’s initialize a SalesAnalyst like this:

sales_analyst = sales_engine.analyst

• sales_analyst.invoice_paid_in_full?(invoice_id) returns true if the Invoice with the corresponding id is paid in full
• sales_analyst.invoice_total(invoice_id) returns the total $ amount of the Invoice with the corresponding id.

Notes:

• Failed charges should never be counted in revenue totals or statistics.
• An invoice is considered paid in full if it has a successful transaction.