Given tables of:
case class Person(id: Int, name: String)
case class Dead(personId: Int)
and populated with:
Person(1, "George")
Person(2, "Barack")
Dead(1)
is it possible to have a single query that would produce a list of (Person, Option[Dead]) like so?
(Person(1, "George"), Some(Dead(1)))
(Person(2, "Barack"), None)
For slick 3.0 it should be something like this:
val query = for {
(p, d) <- persons joinLeft deads on (_.id === _.personId)
} yield (p, d)
val results: Future[Seq[(Person, Option[Dead])]] = db.run(query.result)
In slick, outer joins are automatically wrapped in an Option type. You can read more about joining here: http://slick.typesafe.com/doc/3.0.0/queries.html#joining-and-zipping
Related
I'm trying to create a query like the presented one in the ORM Exposed.
select t.a, t.b, count(*)
from table as t
group by t.a, t.b;
But it seems that .count() supports aliases only for one column, but here I need two columns:
val count = Table.Table.<somehow I need to push both fields a and b here>.count()
Table.Table
.slice(Table.Table.a, Table.Table.b, count)
.selectAll()
.groupBy(Table.Table.a, Table.Table.b)
.map { row ->
Result(
state = row[Table.Table.a],
trigger = row[Table.Table.b],
count = row[count]
)
}
Are you have any ideas on how to do it?
val count = Count(stringLiteral("*"))
This will generate COUNT('*') in your query (which is a valid SQL expression, giving the same result as COUNT(*)).
If you want to get rid of these annoying quotes, you may do the following:
val asterisk = object : Expression<String>() {
override fun toQueryBuilder(queryBuilder: QueryBuilder) {
queryBuilder { +"*" }
}
}
val count = Count(asterisk)
I was trying to convert a query from SQL into Scala code with Slick, but I have got a compiler error in filter clause: constructor cannot be instantiated to expected type.
My code in Slick:
val subquery = (for {
pit <- PassInTripTable.table
t <- TripTable.table if pit.tripNoFk === t.tripNo
} yield (pit, t))
.map{ case (pit, t) => ( pit, Case.If(t.townFrom <= t.townTo).Then(t.townFrom ++ t.townTo).Else(t.townFrom ++ t.townTo) )}
.groupBy(_._1.idPsgFk)
.filter{ case ((pit, count), group) => ( group.map(_._2).countDistinct === 1)}
.map(_._1)
val query = PassengerTable.table.filter(_.idPsg in subquery).map(_.name)
db.run(query.result)
The query in SQL itself:
select name from passenger
where id_psg in
(
select id_psg from trip t,pass_in_trip pit
where t.trip_no=pit.trip_no
group by id_psg
having count(distinct case when town_from<=town_to then town_from+town_to else town_to+town_from end)=1
)
I would be very grateful if someone helped me to find an error.
From looking at your code, it looks like the type you are matching on is not supposed to be "((pit, count), group)".
groupBy in Slick only returns a collection of Tuple2s.
http://slick.lightbend.com/doc/3.0.0/queries.html
So, the filter might look something like...
.filter{ case (pit, count) => ( count.map(_._2).countDistinct === 1)}
The problem is that Slick .groupBy requires a .map call with aggregating functions afterwards. You can find detailed information here.
So, try this:
.groupBy(_._1.idPsgFk)
.map{ case (key, group) => (key, group.map(_._2).countDistinct)}
.filter{ case (_, count) => count === 1}
.map(_._1)
P.S.
I've also found "bad smells" in your code. You get pairs as a result of for-comrehension, but it looks like standard join would be more appropriate here (and more efficient), something like:
PassInTripTable.table.join(TripTable.table).on(_.tripNoFk === _.tripNo)
.map{ case (pit, t) => ...}
And why would you use such condition:
Case.If(t.townFrom <= t.townTo).Then(t.townFrom ++ t.townTo).Else(t.townFrom ++ t.townTo)? Its branches are the same, so equals to t.townFrom ++ t.townTo.
I have a model structure as following:
Group -> Many Parties -> Many Participants
In on of the API calls I need to get single groups with parties and it's participants attached.
This whole structure is built on 4 tables:
group
party
party_participant
participant
Naturally, with SQL it's a pretty straight forward join that combines all of them. And this is exactly what I am trying to do with slick.
Mu method is dao class looks something like this:
def findOneByKeyAndAccountIdWithPartiesAndParticipants(key: UUID, accountId: Int): Future[Option[JourneyGroup]] = {
val joins = JourneyGroups.groups join
Parties.parties on (_.id === _.journeyGroupId) joinLeft
PartiesParticipants.relations on (_._2.id === _.partyId) joinLeft
Participants.participants on (_._2.map(_.participantId) === _.id)
val query = joins.filter(_._1._1._1.accountId === accountId).filter(_._1._1._1.key === key)
val q = for {
(((journeyGroup, party), partyParticipant), participant) <- query
} yield (journeyGroup, party, participant)
val result = db.run(q.result)
result ????
}
The problem here, is that the result is type of Future[Seq[(JourneyGroup, Party, Participant)]]
However, what I really need is Future[Option[JourneyGroup]]
Note: case classes of JourneyGroup and Party have sequences for there children defined:
case class Party(id: Option[Int] = None,
partyType: Parties.Type.Value,
journeyGroupId: Int,
accountId: Int,
participants: Seq[Participant] = Seq.empty[Participant])
and
case class JourneyGroup(id: Option[Int] = None,
key: UUID,
name: String,
data: Option[JsValue],
accountId: Int,
parties: Seq[Party] = Seq.empty[Party])
So they both can hold the descendants.
What is the correct way to convert to the result I need? Or am I completely in a wrong direction?
Also, is this statement is correct:
Participants.participants on (_._2.map(_.participantId) === _.id) ?
I ended up doing something like this:
journeyGroupDao.findOneByKeyAndAccountIdWithPartiesAndParticipants(key, account.id.get) map { data =>
val groupedByJourneyGroup = data.groupBy(_._1)
groupedByJourneyGroup.map { case (group, rows) =>
val parties = rows.map(_._2).distinct map { party =>
val participants = rows.filter(r => r._2.id == party.id).flatMap(_._3)
party.copy(participants = participants)
}
group.copy(parties = parties)
}.headOption
}
where DAO method's signature is:
def findOneByKeyAndAccountIdWithPartiesAndParticipants(key: UUID, accountId: Int): Future[Seq[(JourneyGroup, Party, Option[Participant])]]
Problem when using Slick to join: I have 2 tables User and UserInfo and I want to leftJoin them to get user's info. I've tried this:
val q = for{
(user,info) <- User leftJoin UserInfo on (_.id === _.userid)
} yield(user, info)
But the UserInfo table has some nullable field, so when I try to execute the query:
q.map(user_info => (user_info._1,user_info._2)).list
It makes error because user_info._2 has some null values. I know a solution that yield each field in UserInfo and add getOrElse(None) for nullable fields. However, UserInfo has many field so I don't want to use this.
Can anyone help me?
What you CAN do, is this define a function that does the conversion, and then use it in your map:
def nullToOption[A](input: A): Option[A] = input match {
case null => None
case x => Some(x)
}
And then you just use it in your map.
I made a simple example using a simple list:
val lst = List("Hello", null, "hi", null)
val newlst = map lst nullToOption
newList is now the following: List(Some("Hello"), None, Some("hi"), None)
Of course you can modify nullToOption to fit your needs; here's a version that takes tuples:
def nullToOption[A, B](input: (A,B)): (Option[A], Option[B]) = input match {
case (x, y) => (Some(x), Some(y))
case (x, null) => (Some(x), None)
case (null, y) => (None, Some(y))
case (null, null) => (None, None)
}
I know there are several questions regarding this topic. However; I cannot find one that is directly related to my problem.
I have 3tables in a DB and the PK's from those 3 tables form a composite PK in a XRef table.
I need to be able to select Distinct items based on 2 of the keys just for display on a report.
public IEnumerable<AssemblyPrograms> GetProgramAssemblies()
{
var assembliesList = (from c in eModel.Assemblies.ToList()
join d in eModel.Programs_X_Assemblies_X_Builds
on c.AssemblyID equals d.AssemblyID
join p in eModel.Programs
on d.ProgramID equals p.ProgramID
join a in eModel.AssemblyTypes
on c.AssemblyTypeID equals a.AssemblyTypeID
select new AssemblyPrograms
{
AssemblyID = c.AssemblyID
,ProgramID = d.ProgramID
,AssemblyName = c.AssemblyName
,AssemblyPrefixName = c.AssemblyPrefixName
,ProgramName = p.ProgramName
,AssemblyTypeName = a.AssemblyTypeName
,AssemblyTypeID = a.AssemblyTypeID
});
return assembliesList;
}
This is my query and what I need to pull out of the tables
In my XRef table I have AssemblyID, ProgramID and BuildID as my composite PK.
There can be a many-many relationship from AssemblyID to ProgramID. The BuildID is the key that separates them.
I need to pull Distinct AssemblyID to ProgramID relationships for my report, the BuildID can be ignored.
I have tried .Distinct() in my query and a few other things to no avail.
I would appreciate any help anyone could give me.
Thanks
How about a Distinct overload that accepts a custom equality comparer? Something like this:
class AssemblyComparer : EqualityComparer<AssemblyPrograms> {
public override bool Equals(AssemblyPrograms x, AssemblyPrograms y) {
return x.ProgramID == y.ProgramID && x.AssemblyID == y.AssemblyID;
}
public override int GetHashCode(AssemblyPrograms obj) {
return obj.ProgramID.GetHashCode() ^ obj.AssemblyID.GetHashCode();
}
}