At Mind Candy there are a number of internal websites used for reporting and communication. For example – reading automated build/test status via some REST APIs and turning this into a nice visual status display for large ‘build screens’. These have been authored in Scala using the Play Framework 1.2.x.
Recently, version 2.0 of the Play Framework came out of beta and so I wanted to convert the existing Play 1.2 websites over to it. Amongst other reasons, the ability to build to a .jar file makes for simpler deployment, which I was keen to have.
I couldn’t find a good guide for migrating from 1.x -> 2.0 so I am sharing my experiences of porting a Scala Play 1.2.x application. I expected that it wouldn’t be too hard as I was already using Scala Templates and controllers. That was mostly true, with a couple of issues.
I did find a handy conversion guide on the Play 2 wiki which can help converting some uses (it has some unfortunate formatting though so I’d recommend copying and pasting it)
Starting the project
I’d previously installed Play via brew so an upgrade was as simple as
brew update
brew upgrade play
This installed Play 2 whilst leaving Play 1.2.4 also installed for easy roll-back for developing older stuff if I need it.
For simplicity and because there were various code changes that I knew I needed to make, I created a new site in a new location using play new. However I then used svn copy to copy over source assets and code before modifying. This means in the future I can pull updates down using “svn merge” as work continued on the old site whilst I was porting it over!
All of the public files which aren’t built – javascript, css, images – were simply copied across. In the future I’ll check Play’s support for LESS CSS and the Google Closure JS compiler but for now I just want to get things working.
Initially I copied across all the controllers, models and views and configuration files, though I expected to have to fix those up as the syntax had changed.
After a quick run of play compile I had a whole host of build errors, unsurprisingly. So to cut these down I commented out a lot of the logic – all the routes except the home page /, all the templates and all the controllers except for those needed by the home page.
I fixed up controller in turn and gradually re-enabled the routes, until I hit an issue with Database models that stopped me from migrating the rest of my application (see below)
Migrating dependencies
There were a number of java libraries used by the web app, for example to talk to a Subversion server. (This is one of the reasons I really like Scala – it’s easy to pull in useful Java libraries) In Play 1 that was defined in dependencies.yml, e.g.:
require:
- org.tmatesoft.svnkit -> svnkit 1.3.7
- org.tmatesoft.svnkit -> svnkit-javahl16 1.3.7
repositories:
- tmatesoft:
type: iBiblio
root: "http://maven.studio:8081/nexus/content/repositories/tmatesoft"
contains:
- org.tmatesoft.svnkit -> *</code>
Play 2 now uses sbt as its build system and thus uses the standard sbt syntax for dependencies, so I edited the the project/Build.scala file to add dependencies:
object ApplicationBuild extends Build {
// some definitions omitted
val appDependencies = Seq(
"org.tmatesoft.svnkit" % "svnkit" % "1.7.4",
"org.tmatesoft.svnkit" % "svnkit-javahl16" % "1.7.4",
)
val main = PlayProject(appName, appVersion, appDependencies, mainLang = SCALA).settings(
resolvers += "TmateSoft Repository" at "http://maven.tmatesoft.com/content/repositories/releases/",
)
}
Once the sbt syntax is understood it’s a reasonably simple process to convert dependencies across.
The original play run / test / start / stop command still work, which is helpful. It’s also quite useful to simply run play to get an sbt console and then run ~test which runs test and then re-runs them anytime a source file changes, which is very useful.
For IDE integration, I use IntelliJ IDEA and happily there is an idea command in Play’s SBT which generates an IntelliJ module which has any library dependencies included. However, your code has to build correctly before this works and you probably need to remember to re-run this every time you modify a dependency. If you don’t the IDE won’t show types correctly – typically you will get more ‘false negatives’ of errors showing up in the IDE which will not happen within Play itself.
Migrating the routes file
For some reason the old Routes file had an explicit 404 for the for the favicon. There didn’t seem to be an obvious pure route-based replacement for this and I didn’t need that behaviour so removed the route.
I had to add controllers. to all routes as the full package reference seems to be required now.
e.g. home page changed from
GET / Application.index
to
GET / controllers.Application.index
The syntax for ‘public’ files has changed so I replaced
GET /public/ staticDir:public
with
GET /public/*file controllers.Assets.at(path="/public", file)
I was also serving a single file elsewhere – multiple Assets.at() in the routes file didn’t go well, but I was able to call to add a new method to the Application e.g. ‘serveMyFile’ and then set the routing to be controller.Application.serveMyFile in routes and then have that call the Assets.at() method
e.g.
GET /myfile controllers.Application.serveMyFile
in the Application controller:
def serveMyFile = controllers.Assets.at(path="/path/to/it", file="myfilename.json")
The syntax for parameters in routes has changed and I found that I needed to move the default parameter definitions from the Controller out to the Routes file, using the ?= syntax instead of the Option[T] syntax I had before. That wasn’t hard to do but was slightly irritating in some ways – I’m still not sure if I like having so it in the routes file.
Minor changes to the syntax for parsing out ids from the URL, for example:
GET /versionone/stories/{projectId} versionone.Printer.storiesById
changed to
GET /versionone/stories/:projectId controllers.versionone.Printer.storiesById(projectId: String, timeboxId: String ?= "", template: String ?= "")
Note the additional default parameters being passed. Also in this instance the Id is actually a string, not an Int.
Migrating Controllers
A lot of the package names have changed e.g. play -> play.api so some of the imports needed to be fixed up with the new ‘api’
replaced
import play._
import play.mvc._
with
import play.api._
import play.api.mvc._
With the paths to generated views also changed, I removed lines like import views.Application._
Then with imports fixed up I could then fix up the actual controller code to return an Action and
adding Ok(views.html. … )
e.g. from
def index = {
html.index()
}
to
def index = Action {
Ok(views.html.Application.index())
}
As I mentioned earlier, some changes to controllers were needed because the routes file now supplies default parameters, and I took out some use of the Option[T] type — though as this was generally a String, the empty string works very well as an equivalent to None.
In some controllers I’ve implemented an OAuth callback to read from a Google Calendar – eventually I’d like to play with the built-in OAuth support in Play 2 but in the interest of getting things working quickly I wanted to port over my current code. In order to send a url for Google auth to use as a callback I am calling Router.getFullUrl() but this doesn’t work in Play 2, instead one calls the automatically generated route classes instead. To turn this into a full url you call .absoluteUrl(), but you must remember to add the implicit request to your controller code in order to give this the context needed to generate the url.
e.g. the original code was approximately:
object MyController extends Controller {
def request = {
val callbackUrl = Router.getFullUrl(“MyController.callback”)
// send web request using callbackUrl
}
def callback = {
// handle request
}
}
the new Play 2 code is:
object MyController extends Controller {
def request = Action { implicit request =>
val callbackUrl = routes.MyController.callback().absoluteURL()
// send web request using callbackUrl
}
def callback = Action {
// handle request
}
}
This is more robust because that reverse-lookup is now checked at compile time, rather than runtime. However if your code doesn’t build, your IDE will give you errors as the reverse routes don’t exist. I did occasionally have to do a clean build to force regeneration of reverse-lookups, if the code structure had changed significantly.
Migrating Views
I had to replace @asset() with @routes.Assets.at()
Old references to actions can now be replaced with the compile-time checked generated routing objects. But the snag that isn’t documented is that if you are using a sub-project, the routes are generated within the scope of that sub-project.
e.g. replace @action(svn.Sizes.index()) with @controllers.svn.routes.Sizes.index()
This was mentioned on the Play discussion group here.
Migrating Tests
Unfortunately the bundled Play test framework has changed from scalatest to specs2. I could possibly have set up scalatest to work but decided to migrate the tests instead as the new functional tests look useful, as is the ‘property’ support in specs2.
A few imports change – I had to get rid of the scalatest imports and add in:
import org.specs2.mutable._
import play.api.test._
import play.api.test.Helpers._
The test class now simply extends Specification and I had to fiddle around with the syntax, replacing it with a noun and adding some more braces. should be(x) was replaced with mustEqual x
For example:
it should "retrieve svn server prefix" in {
val svnServers = SvnServer.find().list()
svnServers.length should be > (0)
}
becomes:
"SvnServer" should {
"retrieve svn server prefix" in {
val svnServers = SvnServer.find().list()
svnServers.length must be_>(0)
}
}
There is a good list of all the matchers in specs2 at the specs2 site which I found very useful.
I migrated some very basic selenium tests to the new functional test framework – documented here. The advantage of this is that you can separately test the controller, view and the whole thing together with the router.
The old selenium test was
#{selenium 'Home page'}
// Open the home page, and check that no error occured
open('/')
assertNotTitle('Application error')
#{/selenium}
So a simple test that the home page works is:
class ApplicationTest extends Specification {
"The Application" should {
"render template correctly " in {
val html = views.html.Application.index()
contentType(html) must equalTo("text/html")
val content = contentAsString(html)
content must contain ("Welcome to the Tools website")
content must not contain ("Application error")
}
"have a working controller" in {
val result = controllers.Application.index()(FakeRequest())
status(result) must equalTo(OK)
contentType(result) must beSome("text/html")
charset(result) must beSome("utf-8")
val content = contentAsString(result)
content must contain ("Welcome to the Tools website")
content must not contain ("Application error")
}
"run in a server" in {
running(TestServer(3333)) {
await(WS.url("http://localhost:3333").get()).status must equalTo(OK)
}
}
}
}
Migrating the Database Models – problems!
Now for the bad news… our database models were making heavy use of the Magic[T] class and that simply isn’t present in Play 2.0 at the moment (Apparently it featured in a beta version but was removed). What Magic[T] did was generate a lot of the code for the CRUD operations from a simple case class. For reference in the old documentation for the play-scala-0.9.1, this is what Magic did.
Whilst I could write all of this code myself, I have about 40 classes to do this for, so this is a non-trivial amount of work.
I also discovered that the DB evolution hashes are different, so play wanted to revert and re-apply all of my DB schema changes, which would have trashed the DB contents. Apparently this is now fixed in the trunk in Play 2 so hopefully that change will be in a release soon.
Because I don’t have the time to rewrite all the DB classes, I decided to split my application into two parts, as there are a number of very independent reports in the site which do not use the DB. The reports will be in a play 2 site and the older code that uses the DB will stay as a Play 1.2 site.
In the future I would like to port everything to Play 2. I’m hoping that someone will reintroduce Magic[T], either into the core of Play 2 or as an additional bit of code / plugin. Alternatively I’ll have to do all the grunt work myself, which would be a shame. It’s the kind of work I like to avoid simply because there is very little value I can add – it will either keep working or (more likely) I will break something! So the best option is to leave this old ‘legacy’ site as play 1.2 until there is an easier/safer upgrade path.
However, I will definitely be using Play 2.0 for new development!
