How to update column with another subquery value in Slick? - scala

Question

I want to do something like this
UPDATE item
SET value = (
SELECT max(value)
FROM item
)
WHERE id = 1;
I tried
for {
maxValue <- Tables.Item.map(_.value).max
x <- Tables.Item
.filter(item => item.id === 1)
.map(_.value).update(maxValue)
} yield x
but maxValue is a Rep[Int] instead of Int

Answer 1

Slick's update doesn't support dynamic values or sub-queries. You have a couple of options for this situation.
First, you can use Plain SQL:
sqlu""" UPDATE item SET value = (SELECT max(value) FROM item) WHERE id = 1 """
Second, you could run the expression as two queries (potentially inside a transaction). This is similar to the example you have as update is a DBIO, rather than a Query.
I'd expect max to have an optional value as there might be no rows in the table:
val updateAction: DBIO[Int] =
Tables.Item.map(_.value).max.result.flatMap {
case Some(maxValue) =>
Tables.Item
.filter(item => item.id === 1)
.map(_.value).update(maxValue)
case None =>
DBIO.successful(0) // ... or whatever behaviour you want
}
However, perhaps your value field is already an option and you can use your existing for comprehension with the addition of .result on the end of the maxValue expression as mentioned by #Duelist.