Getting Started with Active Merchant

Before getting started using Active Merchant, a bit of terminology is needed.

In order to process credit card payments, your application needs to interface with a payment gateway. In Active Merchant, these are represented as subclasses of ActiveMerchant::Billing::Gateway.

Gateway Operations

A typical interaction consists of the application obtaining the necessary credit card credentials (card number, expiry date, etc.) and asking the gateway to authorize the required amount on the card holder's credit card.

If the authorization is successful, the funds are available and you can ask the gateway to capture them to your account. If the capture is completed, the payment has been made.

When combined into a single operation, this is called a purchase.

All of these operations are performed on an instance of a Gateway subclass:

gateway = SomeGateway.new

# Amounts are always specified in cents, so $10.00 is 1000 cents
response = gateway.purchase(1000, credit_card)

All three #authorize, #capture and #purchase methods return a ActiveMerchant::Billing::Response instance. This object contains the details of the operation, most notably whether it was successful.

if response.success?
  puts "Payment complete!"
else
  puts "Payment failed: #{response.message}"
end

Handling Credit Cards

In Active Merchant, credit cards are represented by instances of ActiveMerchant::Billing::CreditCard. Instantiating such an object is simple:

credit_card = ActiveMerchant::Billing::CreditCard.new(
  :first_name => 'Steve',
  :last_name  => 'Smith',
  :month      => '9',
  :year       => '2014',
  :type       => 'visa',
  :number     => '4242424242424242')

Most often, though, you'll be using user-supplied data. In a typical Rails controller:

credit_card = ActiveMerchant::Billing::CreditCard.new(params[:credit_card])

Validation

While the above attributes are always required for a CreditCard to be valid, some gateways also require a verification value, e.g. a CVV code, to be given.

Validating a credit card is as simple as calling CreditCard#valid?, which returns true only if the credentials are syntactically valid. If there are any errors or omissions, the CreditCard#errors attribute will be non-empty.