Our latest site with Drupal Commerce 1.x went live in July 2016. It is Freitag. Since then we've been adding several new commerce related features. I feel it's time to write a wrap-up. The site has several interesting solutions, this article will focus on commerce.

First a few words about the architecture. platform.sh hosts the site. The stack is Linux + nginx +  MySQL + PHP, the CMS is Drupal 7. Fastly caches http responses for anonymous users and also for authenticated users having no additional role (that is, logged-in customers). Authcache module takes care of lazy-loading the personalized parts (like the user menu and the shopping cart). Freitag has an ERP system to which we connect using the OCI8 PHP library. We write Behat and simpletest tests for QA.

We use the highly flexible Drupal Commerce suite. 23 of the enabled Freitag contrib modules have a name starting with ‘commerce'. We applied around 45 patches on them. Most of the patches are authored by us and 15 of them have already been committed. Even with this commitment to solve everything we could in an open-source way we wrote 30.000+ lines of commerce-related custom code. Still, in March 2016 Freitag was the 3rd largest Drupal customer contributor.

The words ‘product' and ‘product variation'  I'll be using throughout the article correspond to ‘product display node' and ‘product' in Drupal Commerce lingo.

ERP

ERP is the source of all products and product variations. We import this data into Drupal on a regular basis using Feeds. (Now I would use Migrate instead, it's better supported and easier to maintain.) ERP also lets Drupal know about order status changes, sends the shipping tracking information and informs Drupal about products sent back to Freitag by customers.

There is data flowing in the opposite direction as well. ERP needs to know about all Drupal orders. Also, we create coupons in Drupal and send them to ERP too for accounting and other reasons.

Emails

We send commerce-related emails using the Message stack. This way we can have order-related tokens in our mails and we can manage and translate them outside the Rules UI. Mandrill takes care of the mail delivery.

Payment gateway

It was a client requirement to use the Swiss Datatrans payment gateway. However, at the time of starting  the project, Commerce Datatrans (the connector module on drupal.org) was in dev state and lacked several features we needed. Pressed for time we opted for buying a Datatrans Drupal module from a company offering this solution. It turned out to be a bad choice. When we discovered that the purchased module still does not cover all our needs and looked at the code we found that it was obfuscated and pretty much impossible to change. Also, the module could be used only on one site instance which made it impossible to use it on our staging sites.

We ended up submitting patches to the Commerce Datatrans module hosted on drupal.org. The module maintainer, Sascha Grossenbacher (the well-known Drupal 8 core contributor) helped us solving several issues and feature requests by reviewing our patches. This process has lead to a stable release of Commerce Datatrans with a dozen of feature improvements and bugfixes.

Additional to Datatrans we use Commerce Custom Offline Payments to enable offline store purchases by store staff and bank transfer payments.

Currencies

The site works with 7 different currencies, some of them having two different prices depending on the shipping country. Prices come from ERP and we store them in a field collection field on the product. We do not use the _commerceprice field on the product variation.

Tax

Freitag ships to countries all around the world. VAT calculations are performed for EU, Switzerland, UK, Japan, South Korea and Singapore. To implement this functionality our choice fell on the commerce_vat module. Adding commerce_eu_vat and commerce_ch_vat released us from having to maintain VAT rates for EU and Switzerland ourselves. For the 3 Asian countries we implemented our own _hook_commerce_vat_rateinfo().

We have two different VAT rates for most of the countries. This is because usually a lower VAT rate applies to books. Drupal imports the appropriate VAT rate from the ERP with the product variation data. This information is handled by price calculation rules in Drupal.

Shipping

Freitag delivers its products using several shipping providers (like UPS, Swiss Post) all around the world. Most shipping providers have many shipping rates depending on the destination country, speed and shipped quantity (weight or volume). On checkout the customer can choose from a list of shipping services. This list needs to be compatible with the order.

We used rules to implement the shipping services in Drupal based on the Commerce Flat Rate module. For this end we trained our client to set up and maintain these rules themselves. It was not easy: shipping rules are daunting even for experienced commerce developers. First we needed to set up the “Profile Address” rules components. Then we configured the “Place of Supply” components. We applied these in turn in the condition part of the shipping rules components themselves.

The weakest point of any  implementation based on Rules is the maintenance. It's not easy to find a specific rule after you created it. Having 250 rules components for only shipping made this feeling stronger.

The shipping line item receives the VAT rate of the product with the highest VAT rate in the order.

Coupons

Freitag has 6 different coupon types. They differ in who can create them, who and where (online/offline) can redeem them, whether partial redemption is possible, whether it's a fixed amount or percentage discount and whether Freitag accounting needs to know about them or not.

Based on these criteria we came up with a solution featuring Commerce Coupon. Coupons can be discount coupons or giftcards. Giftcard coupons can only have a fixed value. Discount based coupons can also apply a percentage discount. The main difference between them is that customers can partially redeem giftcards, while discount-based coupons are for one-time use.

To make coupons work with VAT was quite tricky. (To make things simpler we only allowed one coupon per order.) Some coupon types work as money which means that from an accounting point of view they do not actually decrease the order total (and thus the VAT) but work as a payment method. Other coupon types however do decrease the order total (and thus the VAT). At the same time Drupal handles all coupons as line items with a negative price and the Drupal order total does decrease in either case.

The solution we found was to use Commerce proportional VAT.  Axel Rutz maintains this brilliant little module and he does this in a very helpful and responsive manner. All the module does is adding negative VAT price components to coupon line items to account for VAT decrease. It decreases the order total VAT amounts correctly even if we have several different VAT rates inside the order.

Conclusion

Although there's always room for increasing the complexity of the commerce part of the site (let's find some use case for recurring payments!), it's already the most complicated commerce site I've worked on.  For this Drupal Commerce provided a solid foundation that is pleasant to work with. In the end, Drupal enabled us to deliver a system that tightly integrates content and commerce.

I also would like to say thanks to  Bojan Živanović from Commerce Guys who provided me with valuable insights on the legal aspects of tax calculation.