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@julienrf
Last active September 29, 2021 21:38
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Surgical updates in Slick
import slick.lifted.TupleShape
import slick.driver.H2Driver.api._
import scala.concurrent.Await
import scala.concurrent.duration.DurationInt
import scala.concurrent.ExecutionContext.Implicits.global
object Example {
val db = Database.forConfig("db")
// --- Schema definition
class UserTable(tag: Tag) extends Table[(Long, String, Int)](tag, "user") {
def id = column[Long] ("user_id", O.PrimaryKey)
def name = column[String]("name")
def age = column[Int] ("age")
def * = (id, name, age)
}
val users = TableQuery[UserTable]
// --- The interesting part starts here
def updateUser(id: Long, maybeNewName: Option[String], maybeNewAge: Option[Int]): DBIO[Int] =
SurgicalUpdate(users.filter(_.id === id))
.update(_.name, maybeNewName)
.update(_.age, maybeNewAge)
.run()
updateUser(1, Some("jrf"), None) // UPDATE user SET name = 'jrf' WHERE user.user_id = 1
updateUser(1, None, Some(30)) // UPDATE user SET age = 30 WHERE user.user_id = 1
updateUser(1, Some("Julien"), Some(29)) // UPDATE user SET name = 'Julien', age = 29 WHERE user.user_id = 1
// --- Implementation details
import scala.language.higherKinds
case class SurgicalUpdate[E, U, C[_]](query: Query[E, U, C], maybeUpdate: Option[SurgicalUpdate.Update[E]]) {
def update[F, G, T](projection: E => F, maybeT: Option[T])(implicit shape: Shape[_ <: FlatShapeLevel, F, T, G]): SurgicalUpdate[E, U, C] =
maybeT match {
case Some(t) =>
val u2 = SurgicalUpdate.UpdateImpl(projection, t)
maybeUpdate match {
case Some(u1) =>
implicit val tupleShape: Shape[_ <: FlatShapeLevel, (u1.F, u2.F), (u1.T, u2.T), (u1.G, u2.G)] =
new TupleShape(u1.shape, u2.shape)
val tupleUpdate = SurgicalUpdate.UpdateImpl((e: E) => (u1.projection(e), u2.projection(e)), (u1.newValue, u2.newValue))
SurgicalUpdate(query, Some(tupleUpdate))
case None =>
SurgicalUpdate(query, Some(u2))
}
case None =>
this
}
def run(): DBIO[Int] =
maybeUpdate match {
case Some(update) =>
import update.shape
query.map(update.projection).update(update.newValue)
case None => DBIO.successful(0)
}
}
object SurgicalUpdate {
def apply[E, U, C[_]](query: Query[E, U, C]): SurgicalUpdate[E, U, C] = SurgicalUpdate(query, None)
trait Update[E] {
type F
type G
type T
implicit def shape: Shape[_ <: FlatShapeLevel, F, T, G]
def projection: E => F
def newValue: T
}
case class UpdateImpl[E, F0, G0, T0](projection: E => F0, newValue: T0)(implicit val shape: Shape[_ <: FlatShapeLevel, F0, T0, G0]) extends Update[E] {
type F = F0
type G = G0
type T = T0
}
}
}
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