Our COO, Edward Hieatt, was recently interviewed on the topic of pair programming, and why it is such a critical component of our software development process here.
You can find the interview at http://www.airpair.com/pair-programming/, along with numerous quotes from current … Read more
A talk by Jacob Maine about collecting, analyzing and presenting very large amounts of data. Introduces the problems of big data, mentions some of the relevant technologies and gives a bit of advice about designing solutions.
Urban Dictionary is a Ruby on Rails application and the 109th most visited site in the country according to Quantcast. Today it runs entirely in the cloud — on Heroku, AWS and Akamai — and per-user costs are lower than … Read more
Amit Levy introduces MemCachier, a scalable cache service for cloud hosted applications available now on Heroku. MemCachier seeks to relieve developers from worrying about provisioning and managing servers, allowing applications to scale up and down seamlessly. MemCachier also provides insights… Read more
Dart is more than a new structured web programming language. Google’s Dart Developer Advocate, Seth Ladd, talks about the philosophy and motivation for this new open source developer platform. There’s an overview of the language, libraries, and tools that help … Read more
Responsive web design is about a lot more than the size of your screen. Kyle Neath, Director of Design for GitHub, talks about about how GitHub handles links, the url bar, partial page updates, and explains why he thinks the … Read more
Agile brings the idea that when designing a product, collaboration produces better results than conflict, but all too often a familiar us-vs-them war breaks out between developers and operations. Devops is a buzzword, but in reduction it means putting the … Read more
Pivotal is proud to announce the release of the databasedotcom gem. Developed in partnership with Heroku and Salesforce, this gem wraps the Force.com REST API in familiar Ruby idioms, making it a snap to create web applications that integrate with your existing Salesforce instance, or even straight Ruby apps that do offline analysis of your Salesforce data.
I will be giving a session at Dreamforce on Tuesday, August 30, introducing the gem and demonstrating how easy it is to integrate into a Rails application. The session is entitled Building and Deploying Great Applications with Salesforce, Ruby, and Heroku, and takes place in Moscone West Room 2008 from 5:00 pm - 6:00 pm.
Hope to see you there!
The Ugly Truth
On a recent project, we had an ActiveRecord model that declared some relationships and callbacks like so:
belongs_to :credit_card before_create :build_credit_card
The intent was that
build_credit_card would build the associated
CreditCard instance, and ActiveRecord's default
:autosave feature on the
belongs_to would save it.
What we discovered was that no
CreditCard object was being persisted. We confirmed that
:autosave is on by default for
belongs_to relationships, so we couldn't immediately understand why the new
CreditCard wasn't being created.
Googling proved futile, so we dove right in to the ActiveRecord source- and boy did we have a good laugh about 10 minutes later.
What we found was that the
:autosave option works by simply declaring a
before_save callback- that makes perfect sense.
In our case, however, we were building the object to be autosaved in a
before_create callback, which ActiveRecords runs after the
before_save callbacks (cf. the callback ordering docs).
So our first problem was that we needed to move the call to
build_credit_card from a
before_create callback to a
before_save :on => :create callback.
Did you catch that? There is a difference between
before_save :on => :create. A big difference.
While I understand the how and why of this, the semantics don't make it obvious. So beware!
Now with our declarations changed to
belongs_to :credit_card before_save :build_credit_card, :on => :create
We ran our tests again, and, still, no love. Ahhh, we've still got an ordering problem. In addition to the ordering semantics detailed in the docs, ActiveRecord also runs callbacks within a single group in the order in which they are declared. So, even though we changed the call to
build_credit_card to occur in a
before_save, it was still occurring after the
before_save callback, because of the declaration order.
Finally, we changed our declarations to
before_save :build_credit_card, :on => :create belongs_to :credit_card
and our tests were happy.
autosavewith any ActiveRecord association, be very careful of callback ordering if you are building or modifying the inverse objects using ActiveRecord callbacks.
before_createisn't ever the same thing as
before_save :on => :create, even if it sounds like it should be.