Subqueries, Having and GroupBy in Slick - sql

I am currently learning Slick. I was trying to translate this query from SQL into Scala:
SELECT name FROM Passenger
WHERE ID_psg in
(SELECT ID_psg FROM Pass_in_trip
GROUP BY place, ID_psg
HAVING count(*)>1)
But I have only managed to write something like this, and it gives compile errors:
PassengerTable.table.filter(_.idPsg in (PassInTripTable.table.map(_.idPsgFk)))
.filter(PassengerTable.table.count(_.name) > 1)
.map(_.name)
I do not really know how to apply count and having on queries in Slick.
So I would be really grateful for some help.

Try
val subquery = PassInTripTable.table.groupBy(p => (p.place, p.idPsgFk))
.map { case ((place, id), group) => (id, group.length) }
.filter { case (id, count) => count > 1 }
.map { case (id, count) => id }
val query = PassengerTable.table.filter(_.idPsg in subquery).map(_.name)
val action = query.result
db.run(action)
http://slick.lightbend.com/doc/3.0.0/sql-to-slick.html#groupby
http://slick.lightbend.com/doc/3.0.0/sql-to-slick.html#subquery
http://slick.lightbend.com/doc/3.0.0/sql-to-slick.html#having

Related

Aliasing count() for several columns in a group by query in Exposed

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)

What SQL query is the equivalent to this function for retrieving a list of unique items

I'm trying to change this function into an SQL query (using Room). The goal is to return a list of items with no duplicates.
A duplicate is defined by either the item.id or any combination of linked ids being present.
fun removeDuplicates(items: List<Table>?) : List<Table>?{
val returnItems = ArrayList<Table>()
items?.distinctBy { _item ->
_item.id
}?.forEach { item ->
val LID1 = item.linked_id_1
val LID2 = item.linked_id_2
val isFoundReturnItem = returnItems.firstOrNull {
(it.linked_id_1 == LID2 && it.linked_id_2 == LID1) ||
(it.linked_id_1 == LID1 && it.linked_id_2 == LID2)
}
//only add to our new list if not already present
if(isFoundReturnItem == null)
returnItems.add(item)
}
return returnItems
}
If I read your question right here is the answer for Microsoft SQL. Structure:
Select Distinct Field1, Field2, ...
From Table
Where Field1 between 'a' and 'm'
Your Script: The distinct command makes distinct rows.
Select Distinct Item
From YourTableName
You can also use GROUP BY this allows aggregations on distinct values
Select Field1, Field2 = max(Field2), ...
From Table
Where Field1 between 'a' and 'm'
Group by Field1

Constructor can not be instantiated Slick Scala

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.

Conditional sum in slick (scala)

I'm trying to rewrite following SQL into slick:
SELECT id
SUM(
if (spend > 0, 1, 0)
)
FROM items
GROUP by id
My current code looks similar to this:
items.groupBy(r => r.id).map {
case (id, group) => (id, group.map { r => if (r.spend > 0) 1 else 0 }.sum)
}
But I got following error:
polymorphic expression cannot be instantiated to expected type;
found : [R]slick.lifted.Rep[R]
required: Boolean
I also tried to use filter and length, but with no success. How can I achieve my goal?
Slick already provides solution for this (documentation):
items.groupBy(r => r.id).map {
case (id, group) => (id, group.map { r =>
Case If r.spend > BigDecimal(0.0) Then 1 Else 0
}.sum)
}
Scala ternary expression could not be transferred to slick syntax.
Simplest approach is just to simplify the query here to
SELECT COUNT(id)
FROM items
WHERE spend > 0
GROUP by id
Corresponding slick will be
items.filter(_.spend > 0).groupBy(_.id) map {
case (id, group) => (id, group.size)
}
Or you could try to get access to the if function using SimpleFunction:
def ifFun[T] = SimpleFunction.ternary[Boolean, T, T, T]("if")
items.groupBy(_.id) map {
case (id, group) => (id, group.map(r => ifFun(r.spend > 0, 1, 0)).sum)
}

How to convert this SQL to LINQ or Lambda expression?

here's my sql query below:
Can you guys help me to convert this to a much cleaner one??
SELECT [PurchaseRequestID], [ProjectID],[FullName]
FROM PurchaseRequest
WHERE [PurchaseRequestID] IN
(SELECT [PurchaseRequestID] FROM PurchaseRequestDetail )
AND [PurchaseRequestID] NOT IN
(SELECT [PurchaseRequestID] FROM [PurchaseOrder] )
Though i have already converted this successfuly, i think this is not readable and needs to be rewritten:
var query = from a in db.PurchaseRequests
where
(from b in db.PurchaseRequestDetails
select new
{
b.PurchaseRequestID
}).Contains(new { a.PurchaseRequestID }) &&
!(from c in db.PurchaseOrders
select new
{
c.PurchaseRequestID
}).Contains(new { a.PurchaseRequestID })
select a;
thanks
you really don't need all those anonymous objects. Use the let keyword to introduce temporary variables instead of doing operations on the subqueries directly.
from a in db.PurchaseRequests
let b = from b in db.PurchaseRequestDetails select b.PurchaseRequestID
let c = from c in db.PurchaseOrders select c.PurchaseRequestID
where b.Contains(a.PurchaseRequestID) && !c.contains(a.PurchaseRequestID)
select a;
var query = from a in db.PurchaseRequests
where
db.PurchaseRequestDetails.Any(x => x.PurchaseRequestID == a.PurchaseRequestID) &&
!db.PurchaseOrders.Any(x => x.PurchaseRequestID == a.PurchaseRequestID)
select a;
If you have navigation properties set up, you can write the query like this:
IQueryable<PurchaseRequest> query =
from purchaseRequest in myDataContext.PurchaseRequests
where purchaseRequest.PurchaseRequestDetail.Any()
where !purchaseRequest.PurchaseOrder.Any()
select purchaseRequest;
Or this lambda/method style if you prefer...
IQueryable<PurchaseRequest> query2 = myDataContext.PurchaseRequests
.Where(purchaseRequest => purchaseRequest.PurchaseRequestDetail.Any())
.Where(purchaseRequest => !purchaseRequest.PurchaseOrder.Any());