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 ReadOnlyNamedAutoSession is also available.
These auto sessions disallow update/execute operations.