I spent a wee while yesterday kicking the tyres on the Play 2.0 framework with Scala. Aside: I think that concurrency/asynchronous processing is really important in the age of multi-core CPUs, and that Akka’s actor-based system is really interesting, and Play uses Akka 2 under the hood, so I’m becoming really interested in becoming proficient in Scala & Play 2. That said, so far I’m struggling to come to terms with Scala’s type system, and it reminds of the struggles I had with ML at University, so this could be an uphill battle!
Anyway, that’s not what this is about. The toy application I’m trying to build (which I’ll share if and when I’m done!) involves storing locations (a latitude and longitude) as decimals. I’ve got my table (stored as an evolution) along the lines of:
(I’m using PostgreSQL.) And here’s the first implementation of the model,
app/models/Site.scala, which just has a
case class to encapsulate the table
data, and a singleton object with a finder to return a sequence of site (so
that I can list them in a table):
(Totally cargo-culted, BTW.) This means that in the controller I should be able
Site.findAll() and get back a sequence of sites I can then use to map
to HTML fragments. Win.
But I’m getting a compilation error! In the browser, it’s saying
find implicit value for parameter extractor: anorm.Column[BigDecimal] and
pointing to the error being on
get(BigDecimal)("sites.latitude") in the
I couldn’t find any documentation on retrieving decimals from a database with anorm (which is mostly why I’m writing this) and looking through the source code didn’t exactly elucidate. However, after a bit of trial and error, I discovered that it works if I add:
at the start of the model file.
So, if you’re having trouble making
BigDecimal columns work in your
Anorm-based models, remember to explicitly
Hopefully this will find its way into Google, making the next Scala newbie’s
introduction a little less painful. :)
I’d love if somebody could explain why. Perhaps it would improve my understanding of Scala!
Update Aha, I have a theory. I think that, by default,
is available in my model’s scope. And
scala.math.BigDecimal isn’t a subtype
java.math.BigDecimal, which is what Anorm deals in. So importing the Java
version overrides the Scala version and makes the type system happy.
Now I’m wondering: why the two unrelated (in type-land anyway) versions of
BigDecimal? Which should my apps be using? Which should Anorm be exposing?