Scala Slick - Convert TableQuery[E] to Query[E] to chain operations - scala

Question

I'm trying to apply a series of optional filtering operations to a query by using a list of the operations and folding over the list.
val table = TableQuery[Fizz]
val filters = List(filter1(option1)_, filter2(option2)_, filter3(option3)_)
val filteredQuery = filters.foldLeft(table){(q, filter) => filter(q)}
The partially applied filter functions have a signature of
Query[Fizz, FizzRow, Seq] => Query[Fizz, FizzRow, Seq]
Basically, in each function, I am optionally applying the filtering if the filter parameter option* is present. However, the compiler does not like the fact that I am passing in a TableQuery to a function that takes Query, even though TableQuery is a subtype of Query. Is there a way to convert a TableQuery to Query? Or a better way to go about chaining filter functions on a query?
The compiler error in question is
type mismatch;
found :scala.slick.lifted.Query[generated.Tables.Farm,generated.Tables.FarmRow,Seq]
required: scala.slick.lifted.TableQuery[generated.Tables.Farm]
I can get it to compile by using table.drop(0) instead of table but obviously that seems like a poor workaround. I see that there's a to method on TableQuery that converts it to a Query but it also takes an implicit ctc: TypedCollectionTypeConstructor[D].
An example of one of the filterX functions listed above:
def filterCharacteristics(characteristics: Option[List[Int]])(table: Query[Farm,FarmRow,Seq]) = {
characteristics.map(chars =>
(for {
(fc, f) <- Farmcharacteristic.filter(_.characteristicId inSet chars) join table on (_.farmId === _.farmId)
} yield f)).getOrElse(table)
}

Answer 1

I think you can try another approach. Instead of using a fold, you can use a collect to get only the Some values.
Then you can apply a filter to each of the options you have:
val table = TableQuery[Fizz]
val filteredQueries = List(Some(option1), Some(option2), Some(option3)) collect {
case Some(option) => option
} map { currentOption =>
table.filter(currentOption)
}
// We need to get the last value or the TableQuery
val lastValue = filteredQueries reverse headOption
// Or we have Some(Query) or None, In case it is a None, we will use table
lastValue.getOrElse(table)