Auto Session


Why AutoSession?


Basic usage of ScalikeJDBC is using DB.autoCommit/readOnly/localTx/withinTx { ...} blocks.

However, if you’d like to re-use methods, they might not be available.

def findById(id: Long) = DB readOnly {
  sql"select id, name from members where id = ${id}"
    .map(rs => Member(rs)).single.apply()
}

When you use the above method in a transaction block, the code won’t work as you expected.

The reason is that since #findById(Long) uses another session(=connection), it couldn’t access uncommitted data.

DB localTx { implicit session =>
  val id = create("Alice")
  findById(id) // Not found!
}

You need to change method’s API to accept implicit parameters and now you don’t need DB block inside the method.

def findById(id: Long)(implicit session: DBSession) =
  sql"select id, name from members where id = ${id}"
    .map(rs => Member(rs)).single.apply()

This one works as expected.

DB localTx { implicit session =>
  val id = create("Alice")
  findById(id) // Found!
}

But unfortunately, now we need to pass implicit parameter to #findById every time to use it.

// now we cannot use this method directly
findById(id) // implicit parameter not found!

DB readOnly { implicit session => findById(id) }

AutoSession is a solution for this issue. Use AutoSession as default value of the implicit parameter.

def findById(id: Long)(implicit session: DBSession = AutoSession) =
  sql"select id, name from members where id = ${id}"
    .map(rs => Member(rs)).single.apply()

This change made #findById flexible.

findById(id) // borrows a read-only session and gives it back
DB localTx { implicit session => findById(id) } // using implicit session

If you do the same with NamedDB, use NamedAutoSession as follows.

def findById(id: Long)(implicit session: DBSession = NamedAutoSession('named)) =
  sql"select id, name from members where id = ${id}"

ReadOnlyAutoSession


Since version 1.7.4, ReadOnlyAutoSession and NamedReadOnlyAutoSession is also available.

These auto sessions disallow update/execute operations.


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