I sum up totals in two different database tables:
val sum1Query: Rep[Int] = tableQuery1.map(_.amount).sum.ifNull(0)
val sum2Query: Rep[Int] = tableQuery2.map(_.amount).sum.ifNull(0)
for {
sum1 <- sum1Query.result
sum2 <- sum2Query.result
} yield {
sum1 + sum2
}
This runs 2 SQL queries to the database each time .result is called. I am looking for a way to make it use only one SQL query.
Something like this doesn't work:
for {
sum1 <- sum1Query
sum2 <- sum2Query
} yield {
sum1 + sum2
}.result
Any ideas on how to do it in Slick other than using plain SQL query?
Each call to .result creates a DBIO action which is a SQL statement. The trick to reducing the number of actions is to find a way to combine two queries (or two Reps) together into one action.
In your case you could zip the two queries:
val sum1 = table1.map(_.amount).sum.ifNull(0)
val sum2 = table2.map(_.amount).sum.ifNull(0)
val query = sum1.zip(sum2)
When run the query.result you'll execute a single query something like:
select ifnull(x2.x3,0), ifnull(x4.x5,0)
from
(select sum("amount") as x3 from "table_1") x2,
(select sum("amount") as x5 from "table_2") x4
...which will result in a tuple of the two values.
However, as you've already just got a Rep[Int] you can use + in the database:
val query = sum1 + sum2
...which will be a query along the lines of:
select ifnull(x2.x3,0) + ifnull(x4.x5,0)
from
(select sum("amount") as x3 from "table_1") x2,
(select sum("amount") as x5 from "table_2") x4
Just put it like this:
(sum1 + sum2).result
Related
I have an optional insert query:
val q = sql"insert into some_table (some_field) select 42 where ...(some condition)"
Running this query with:
q.update.withUniqueGeneratedKeys[Option[Long]]("id")
fails with
Result set exhausted: more rows expected
then condition is false.
How to get Optional[Long] result from insert statements with Doobie?
UPD
.withGeneratedKeys[Long]("id") gives just Long in for comprehension
val q = sql"insert into some_table (some_field) select 42 where ...(some condition)"
for {
id <- q.update.withGeneratedKeys[Long]("id") // id is long
_ <- if (<id is present>) <some other inserts> else <nothing>
} yield id
How to check id?
As #Thilo commented, you can use the use withGeneratedKeys which gives you back a Stream[F, Long] (where F is your effect type)
val result = q.update.withGeneratedKeys[Long]("id")
Here is the doc.
Using Slick 3.1, how do I combine multiple Queries into a single query for the same type? This is not a join or a union, but combining query "segments" to create a single query request. These "segments" can be any individually valid query.
val query = TableQuery[SomeThingValid]
// build up pieces of the query in various parts of the application logic
val q1 = query.filter(_.value > 10)
val q2 = query.filter(_.value < 40)
val q3 = query.sortBy(_.date.desc)
val q4 = query.take(5)
// how to combine these into a single query ?
val finalQ = ??? q1 q2 q3 q4 ???
// in order to run in a single request
val result = DB.connection.run(finalQ.result)
EDIT:
the expected sql should be something like:
SELECT * FROM "SomeThingValid" WHERE "SomeThingValid"."value" > 10 AND "SomeThingValid"."valid" < 40 ORDER BY "MemberFeedItem"."date" DESC LIMIT 5
val q1 = query.filter(_.value > 10)
val q2 = q1.filter(_.value < 40)
val q3 = q2.sortBy(_.date.desc)
val q4 = q3.take(5)
I think you should do something like the above (and pass around Querys) but if you insist on passing around query "segments", something like this could work:
type QuerySegment = Query[SomeThingValid, SomeThingValid, Seq] => Query[SomeThingValid, SomeThingValid, Seq]
val q1: QuerySegment = _.filter(_.value > 10)
val q2: QuerySegment = _.filter(_.value < 40)
val q3: QuerySegment = _.sortBy(_.date.desc)
val q4: QuerySegment = _.take(5)
val finalQ = Function.chain(Seq(q1, q2, q3, q4))(query)
I've used this "pattern" with slick2.0
val query = TableQuery[SomeThingValid]
val flag1, flag3 = false
val flag2, flag4 = true
val bottomFilteredQuery = if(flag1) query.filter(_.value > 10) else query
val topFilteredQuery = if(flag2) bottomFilteredQuery.filter(_.value < 40) else bottomFilteredQuery
val sortedQuery = if(flag3) topFilteredQuery.soryBy(_.date.desc) else topFilteredQuery
val finalQ = if(flag4) sortedQuery.take(5) else sortedQuery
It's Just a worth remark to mention here from the slick essential book, it seems that you might need to avoid combining multiple queries in one single query.
Combining actions to sequence queries is a powerful feature of Slick.
However, you may be able to reduce multiple queries into a single
database query. If you can do that, you’re probably better off doing
it.
I think, it should work. But I didn't test it yet.
val users = TableQuery[Users]
val filter1: Query[Users, User, Seq] = users.filter(condition1)
val filter2: Query[Users, User, Seq] = users.filter(condition2)
(filter1 ++ filter2).result.headOption
I want to force slick to create queries like
select max(price) from coffees where ...
But slick's documentation doesn't help
val q = Coffees.map(_.price) //this is query Query[Coffees.type, ...]
val q1 = q.min // this is Column[Option[Double]]
val q2 = q.max
val q3 = q.sum
val q4 = q.avg
Because those q1-q4 aren't queries, I can't get the results but can use them inside other queries.
This statement
for {
coffee <- Coffees
} yield coffee.price.max
generates right query but is deprecated (generates warning: " method max in class ColumnExtensionMethods is deprecated: Use Query.max instead").
How to generate such query without warnings?
Another issue is to aggregate with group by:
"select name, max(price) from coffees group by name"
Tried to solve it with
for {
coffee <- Coffees
} yield (coffee.name, coffee.price.max)).groupBy(x => x._1)
which generates
select x2.x3, x2.x3, x2.x4 from (select x5."COF_NAME" as x3, max(x5."PRICE") as x4 from "coffees" x5) x2 group by x2.x3
which causes obvious db error
column "x5.COF_NAME" must appear in the GROUP BY clause or be used in an aggregate function
How to generate such query?
As far as I can tell is the first one simply
Query(Coffees.map(_.price).max).first
And the second one
val maxQuery = Coffees
.groupBy { _.name }
.map { case (name, c) =>
name -> c.map(_.price).max
}
maxQuery.list
or
val maxQuery = for {
(name, c) <- Coffees groupBy (_.name)
} yield name -> c.map(_.price).max
maxQuery.list
I have the problem writing query in SLICK
Here is my request to MySql database:
SELECT * FROM readings AS r
JOIN parameters AS p
LEFT JOIN sensorvalues AS sv ON sv.parameter_id=p.id AND sv.reading_id=r.id
How can I write it using SLICK ? It is really lack of info on joins in docs.
UPDATE 1
I tried all the combinations even one like this
val q = for{
Join(p,sv) <- Parameters leftJoin SensorValues on (_.id is sv.parameter_id)
r <- Readings if sv.reading_id is r.id
} yield(r,p,sv)
In this case compiler gives me an error wrong number of parameters; expected = 2
So I replaced sv.parameter_id to _.parameter_id and now it argues about Join
It said that:
constructor cannot be instantiated to expected type; found : models.Join required: (models.Parameters.type, models.SensorValues.type)
I'm using last version of SLICK and it's deprecated. I manually imported
import scala.slick.lifted.Join and now it looks like it's regular innerJoin because it uses WHERE instead of putting and after ON.
SQL generated buy query:
select x2.id, x2.platform_id, x2.date, x3.x4, x3.x5, x3.x6, x7.x8, x7.x9, x7.x10, x7.x11 from (select x12.id as x4, x12.name as x5, x12.units as x6 from parameters x12) x3 left outer join (select x13.id as x8, x13.reading_id as x9, x13.parameter_id as x10, x13.value as x11 from sensorValues x13) x7 on x3.x4 = x7.x10, readings x2 where true and (x7.x9 = x2.id)
Even this one would be good with added condition to the ON section
val readings = for {
all <-Readings join Parameters leftJoin SensorValues on (_._2.id is _.parameter_id) if(all._1._1.id === all._2.reading_id)
} yield (all._1._1,all._1._2,all._2)
But this never hapens.
SELECT
x2.x3,
x2.x4,
x2.x5,
x2.x6,
x2.x7,
x2.x8,
x9.x10,
x9.x11,
x9.x12,
x9.x13
FROM
(
SELECT
x14.x15 AS x3,
x14.x16 AS x4,
x14.x17 AS x5,
x18.x19 AS x6,
x18.x20 AS x7,
x18.x21 AS x8
FROM
(
SELECT
x22.`id` AS x15,
x22.`platform_id` AS x16,
x22.`date` AS x17
FROM
`readings` x22
)x14
INNER JOIN(
SELECT
x23.`id` AS x19,
x23.`name` AS x20,
x23.`units` AS x21
FROM
`parameters` x23
)x18
)x2
LEFT OUTER JOIN(
SELECT
x24.`id` AS x10,
x24.`reading_id` AS x11,
x24.`parameter_id` AS x12,
x24.`value` AS x13
FROM
`sensorValues` x24
)x9 ON x2.x6 = x9.x12
WHERE
x2.x3 = x9.x11
instead WHERE I need AND. What Should I use to mention this condition or there is no functionality in slick for that?
EDIT
The OP is looking for chained on conditions in a join of 2 table objects.
This should compile:
val q = for{
r <- Readings
Join(p,s) <- Params leftJoin Sensors on (
(a,b)=> (a.id is b.parameter_id) && (b.reading_id is r.id)
)
} yield(r,p,s)
ORIGINAL
Try something like this:
val q = for{
Join(p,s) <- Params leftJoin Sensors on (_.id is s.parameter_id)
r <- Readings if s.reading_id is r.id
} yield(r,p,s)
val result =
q.list.map{ case(r,p,s)=>
SomeCaseClass(r,p,s)
}
I have few tables, lets say 2 for simplicity. I can create them in this way,
...
val tableA = new Table[(Int,Int)]("tableA"){
def a = column[Int]("a")
def b = column[Int]("b")
}
val tableB = new Table[(Int,Int)]("tableB"){
def a = column[Int]("a")
def b = column[Int]("b")
}
Im going to have a query to retrieve value 'a' from tableA and value 'a' from tableB as a list inside the results from 'a'
my result should be:
List[(a,List(b))]
so far i came upto this point in query,
def createSecondItr(b1:NamedColumn[Int]) = for(
b2 <- tableB if b1 === b1.b
) yield b2.a
val q1 = for (
a1 <- tableA
listB = createSecondItr(a1.b)
) yield (a1.a , listB)
i didn't test the code so there might be errors in the code. My problem is I cannot retrieve data from the results.
to understand the question, take trains and classes of it. you search the trains after 12pm and you need to have a result set where the train name and the classes which the train have as a list inside the train's result.
I don't think you can do this directly in ScalaQuery. What I would do is to do a normal join and then manipulate the result accordingly:
import scala.collection.mutable.{HashMap, Set, MultiMap}
def list2multimap[A, B](list: List[(A, B)]) =
list.foldLeft(new HashMap[A, Set[B]] with MultiMap[A, B]){(acc, pair) => acc.addBinding(pair._1, pair._2)}
val q = for (
a <- tableA
b <- tableB
if (a.b === b.b)
) yield (a.a, b.a)
list2multimap(q.list)
The list2multimap is taken from https://stackoverflow.com/a/7210191/66686
The code is written without assistance of an IDE, compiler or similar. Consider the debugging free training :-)