In Slick 3.0, how do I simplify the nested `db.run`?
I am using Slick 3.0 and the following are my codes:
def registerMember(newMember: TeamMember): Future[Long] = {
db.run(
teamProfileTable.filter(u => u.ID === newMember.ID).result.headOption
).flatMap {
case None => Future(-1)
case _ => db.run(
(teamProfileTable returning teamProfileTable.map(_.staffID)) += newMember.toTeamRecord
)
}
}
It might look okay. But when there are more callback layers, the codes can become hard to read. I tried to simplify the codes with for-expression
or andThen
.. But because of the pattern matching part I can use flatMap
to implement this.
Does anyone have any ideas on how to refactor this?
I think it should be good to understand, you just need to conditionally handle the Option
result of the former Future
. Something like this should work (note that I did not compile the check):
def registerMember(newMember: TeamMember): Future[Long] = {
for{
r1Opt <- db.run(teamProfileTable.filter(u => u.ID === newMember.ID).result.headOption
r2 <- r1Opt.fold(Future.successful(-1L))(r1 => db.run((teamProfileTable returning teamProfileTable.map(_.staffID)) += newMember.toTeamRecord)
} yield r2
}
On the right side, fold
you can see that I have access to the result of the first one Future
, if it was Some
(like r1
).
I would even take it even further and create separate methods for steps to understand to clean things up, like:
def registerMember(newMember: TeamMember): Future[Long] = {
def findMember =
db.run(teamProfileTable.filter(u => u.ID === newMember.ID).result.headOption
def addMember(r1Opt:Option[TeamMember]) = {
r1Opt.fold(Future.successful(-1L)){r1 =>
db.run((teamProfileTable returning teamProfileTable.map(_.staffID)) +=
newMember.toTeamRecord)
}
}
for{
r1Opt <- findMember
r2 <- addMember(r1Opt)
} yield r2
}
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Another approach to simplifying nested db.runs in Slick 3.0, when a query spans two tables, might be to combine the queries into a single query. Joining and Zipping . However, the OP seems to have a slightly rarer case of nested queries in the same table, so this approach may not be practical in this particular case.
val query = slickLoginInfos join slickUserLoginInfos on
((l,ul) => l.id === ul.loginInfoId)
db.run((for { (l, ul) <- query } yield (ul)).result.headOption)
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