transaction management across several DAOs

[vatel]

I think in some cases it is handy to manage transactions from outside of DAO objects, ex:

class MyBusinessLogic {

def doSomething = {

inTransaction { dao1.create dao2.update ... }

}

I have implemented this functionality for prequel (in a separate class, without patching in fact) and can share it here, Sorry, I am not experienced with github yet, so I could send it to email or post here, just let me know.

[jpersson]

If you want use multiple DAOs within out transaction you have to pass the connection to the DAO instance somehow. Either through the method itself or the constructor.

[vatel]

let me explain a little bit:

Here are that new classes (just fragments):

// to be use in business logic (ie at more high level)
trait TransactionManager {
  def inTransaction[T](block: => T): T
}
// to be used in DAOs
class DatabaseTransactionManager(val db: DatabaseConfig) extends TransactionManager {
def transaction[T](block: (Transaction) => T): T = {...}
override def inTransaction[T](block: => T): T = {
    transaction { tr =>
      block
    }
}

and how I use them:

// this class itself does NOT work with database
class BusinessLogic(
  implicit val dao: SomeDAO,
  implicit val tm: TransactionManager)  {
import tm._
def doSomething = {
  // call DAO method in the same transaction
  inTransaction {
      dao.createSomethin(...)
      dao.updateSomething(...)
      dao.doSomethingElse(...)
  }
}
}
class SomeDAO (implicit tm: DatabaseTransactionManager) {
import tm._
def createSomethin(...) = {
    transaction { tx =>
        tx.execute("insert into ..."...)
    }
}
...
}

DatabaseTransactionManager class implements thread-local stack of currently-running transactions, so the example above executes in the same transaction. I have also added support for 'REQUIRES_NEW' propagation semantic. It works both with one and multiple DAOs inside transaction.

[vatel]

So the issue in fact is about more complicated use-cases of transaction management - when you can do several things (from multiple DAO methods or multiple DAOs) inside the same transaction and you do not want to write heavyweight methods in DAO.