Black Thursday Iteration 2 - Basic Invoices

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Now we’ll begin to move a little faster. Let’s work with invoices to build up the data access layer and business intelligence in one iteration.

Parts to iteration 3: Data Access Layer Business Intelligence

Data Access Layer

InvoiceRepository

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

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

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

se = SalesEngine.from_csv({:invoices => "./data/invoices.csv"})
invoice = se.invoices.find_by_id(6)
# => <invoice>

Invoice

The invoice has the following data accessible:

• id - returns the integer id
• customer_id - returns the customer id
• merchant_id - returns the merchant id
• status - returns the status
• created_at - returns a Time instance for the date the item was first created
• updated_at - returns a Time instance for the date the item was last modified

We create an instance like this:

i = Invoice.new({
  :id          => 6,
  :customer_id => 7,
  :merchant_id => 8,
  :status      => "pending",
  :created_at  => Time.now,
  :updated_at  => Time.now,
})

Business Intelligence

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

sales_analyst = sales_engine.analyst

Then, using the sales_analyst instance, answer the following questions:

How many invoices does the average merchant have?

sales_analyst.average_invoices_per_merchant # => 10.49
sales_analyst.average_invoices_per_merchant_standard_deviation # => 3.29

Who are our top performing merchants?

Which merchants are more than two standard deviations above the mean?

sales_analyst.top_merchants_by_invoice_count # => [merchant, merchant, merchant]

Who are our lowest performing merchants?

Which merchants are more than two standard deviations below the mean?

sales_analyst.bottom_merchants_by_invoice_count # => [merchant, merchant, merchant]

Which days of the week see the most sales?

On which days are invoices created at more than one standard deviation above the mean?

sales_analyst.top_days_by_invoice_count # => ["Sunday", "Saturday"]

What percentage of invoices are not shipped?

What percentage of invoices are shipped vs pending vs returned? (takes symbol as argument)

sales_analyst.invoice_status(:pending) # => 29.55
sales_analyst.invoice_status(:shipped) # => 56.95
sales_analyst.invoice_status(:returned) # => 13.5