I am using Slick 1, and I have to be able to apply a filter in a query to lookup all entities that match a condition in a related table.
This example using the Slick documentation shows what I am trying to do (this is a contrived example that is close to my situation).
Here, I want all coffees that are provided by suppliers on the west coast. I want the Coffee only, I am only interested in navigating to Suppliers to apply the filter:
val westCoast = Seq("CA", "OR", "WA")
val implicitInnerJoin = for {
c <- Coffees
s <- Suppliers if c.supID === s.id && s.state inSet westCoast
} yield c
This works ok, but it will duplicate Coffees if there is more than one match in the Suppliers table.
The obvious workaround is in normal SQL to do a SELECT DISTINCT; however, I cannot find a way to do that here.
You could in theory do a:
query.list.distinct
After the results are already returned; however, I have also implemented PAGING support, so you wouldn't want to process the results once the already come back from the database. Here is the paging support:
query.drop(offset).take(limit).list
So, in a nutshell, I need a way to specify SELECT DISTINCT in my query that goes out.
Anyone have any ideas?
Answer
As a work around you can try to use groupBy:
query.groupBy(x=>x).map(_._1)
It should have the same semantics as distinct, but I'm not sure about performance.