如何重用scala的“ withSession {隐式会话：Session =>”代码块

Question

I have this code in scala using slick

def insertTask(task: Task) = {
  conn.dbObject withSession { implicit session: Session =>
    tasks.insert(task)
  }
}

it looks working :)

Now I'm going to have also code for readTask and I do not want to duplicate the code for withSession { implicit...

So I thought of doing this:

def doWithConn(dbConn: DBConnection, doThisCodeBlock: => Unit)(implicit session: Session) = {
  dbConn.dbObject withSession { implicit session: Session =>
    doThisCodeBlock
  }
}

and now my code looks like

def insertTask(task: Task) = {
  doWithConn(conn, tasks.insert(task)) // here i get the following complication error
}

however I get the following compilation error:

Error:(36, 34) could not find implicit value for parameter session: scala.slick.jdbc.JdbcBackend#SessionDef doWithConn(conn, tasks.insert(task)) ^

I'm not sure how to pass the session from the insertTask method. How can I pass it and fix this compilation error?

thanks

Answer 1

withSession is a method that takes a function from session to whatever as an argument. The syntax { implicit session => } is just to make the session implicit. But you can also just pass a function:

val yourBlock: Session => ... = ...

db.withSession(yourBlock)

No need to wrap it, just use it as is :).

Chris

Answer 2

The problem I think is your doThisCodeBlock doesn't have a notion of a session being passed to it. I think a better way is to simply use currying for reusing statements that use the session:

def insertTaskStatement(task: Task)(implicit session: Session) = {
    tasks.insert(task)
}

def insertOtherThingStatement(otherThing: OtherThing)(implicit session: Session) = {
    things.insert(otherThing)
}

def insertTaskAndOtherThing(task: Task,otherThing: OtherThing) = {
  conn.dbObject withSession { implicit session: Session =>
    insertTaskStatement(task)
    insertOtherThingStatement(otherThing)
  }
}