Inject database connection pool

Question

I have started using MacWire for the dependency injection of my Play app, and I am having problems trying to inject the database connection.

Before using DI, my code looked like this:

DB.withConnection { implicit connection =>
  ...
}

This is not working anymore after using DI. I get the following exception: java.lang.InstantiationException: play.api.db.DBApi.

My application loader:

class Loader extends ApplicationLoader {
  def load(context: Context) = {
    val components = new BuiltInComponentsFromContext(context) with Components
    components.application
  }
}

The main components of the app:

trait Components extends BuiltInComponents with I18nComponents
                 with RepositoryModule {

  lazy val assets: Assets = wire[Assets]
  lazy val router: Router = wire[Routes] withPrefix "/"
}

And the repository module:

trait RepositoryModule {
  lazy val userRepository = wire[UserRepository]
}

How can I get and use a database connection pool and inject it so it can be used within the repository?

Similar situation with compile time DI and connection pool instantiation -- were you able to resolve this? — virtualeyes, Nov 20 '15 at 16:53
Yes. Look at my own answer. It can be improved but it solved my problems. — Miguel, Nov 20 '15 at 20:48

score 2 · Accepted Answer · answered Nov 20 '15 at 20:47

I solved it using the DBComponents and BoneCPComponents traits in the RepositoryModule. With them, I could get a Database object and inject it to the repositories. This is the code I'm using for the module:

trait RepositoryModule extends BuiltInComponents with DBComponents with BoneCPComponents {
  lazy val database: Database = dbApi.database("default")
  lazy val userRepository = wire[UserRepository]
}

The database "default" will use the db.default configurations in the application.conf. The main problem with this solution is that you need to get the connections from the pool and return them when you're done. I don't know if it can be improved to mimic the withConnection method.

An example of the user repository using the injected database:

class UserRepository(db: Database) {
  def deleteAdults: Unit = {
    val connection: Connection = db.getConnection()
    val removed: Int = SQL("DELETE * FROM User WHERE age > 18").executeUpdate()(connection)
    connection.close()
  }
}

Found similar in MacWire's [play sample project](https://github.com/adamw/macwire/blob/master/examples/play24/app/com/softwaremill/play24/modules/DatabaseModule.scala). Play compile time DI docs are really sparse, would be nice to have a list of available DI components :\ — virtualeyes, Nov 21 '15 at 07:07
re: closing connections, I suspect most play-ers are using Slick or other query dsl that handles resource management. — virtualeyes, Nov 21 '15 at 07:12

Inject database connection pool

1 Answers1