Scala SQL DSL (Internal/External) - sql

Question

I have been looking into scala primarily on how to build DSL similar to C# LINQ/SQL. Having worked with C# LINQ Query provider, it was easy to introduce our own custom query provider which translated LINQ query to our own proprietary data store scripts. I am looking something similar in scala for eg.
val query = select Min(Close), Max(Close)
from StockPrices
where open > 0
First of all is this even possible to achieve in scala using internal DSL.
Any thoughts/ideas in this regard is highly appreciated.
I am still new in scala space, but started looking into Scala MetaProgramming & Slick. My complaint with Slick is i want to align my DSL close to SQL query - similar to above syntax.

Answer 1

There is no way to have an internal DSL (with the currently release) that looks exactly like the example you provided.
Using a macro I still had from this answer, the closest I could get (relatively fast) was:
select(Min(StockPrices.Open), Max(StockPrices.Open))
.from(StockPrices)
A real solution would take quite some time to create. If you are willing to do that you could come quite far using macro's (not a simple topic).
If you really want the exact same syntax I recommend something like XText that allows you to create a DSL with an eclipse based editor for 'free'.
The code required for the above example (I did not include the mentioned macro):
trait SqlElement {
def toString(): String
}
trait SqlMethod extends SqlElement {
protected val methodName: String
protected val arguments: Seq[String]
override def toString() = {
val argumentsString = arguments mkString ","
s"$methodName($argumentsString)"
}
}
case class Select(elements: Seq[SqlElement]) extends SqlElement {
override def toString() = s"SELECT ${elements mkString ", "}"
}
case class From(table: Metadata) extends SqlElement {
private val tableName = table.name
override def toString() = s"FROM $tableName"
}
case class Min(element: Metadata) extends SqlMethod {
val methodName = "Min"
val arguments = Seq(element.name)
}
case class Max(element: Metadata) extends SqlMethod {
val methodName = "Max"
val arguments = Seq(element.name)
}
class QueryBuilder(elements: Seq[SqlElement]) {
def this(element: SqlElement) = this(Seq(element))
def from(o: Metadata) = new QueryBuilder(elements :+ From(o))
def where(element: SqlElement) = new QueryBuilder(elements :+ element)
override def toString() = elements mkString ("\n")
}
def select(args: SqlElement*) = new QueryBuilder(Select(args))
trait Column
object Column extends Column
object tables {
object StockPrices$ {
val Open: Column = Column
val Close: Column = Column
}
val StockPrices = StockPrices$
}
And then to use it:
import tables._
import StockPrices._
select(Min(StockPrices.Open), Max(StockPrices.Open))
.from(StockPrices)
.toString

Answer 2

That is an admirable project, but one that has been embarked upon and which is available in general release.
I'm talking about Slick, of course.

Answer 3

If Scala / Java interoperability is not too much of an issue for you, and if you're willing to use an internal DSL with a couple of syntax quirks compared to the syntax you have suggested, then jOOQ is growing to be a popular alternative to Slick. An example from the jOOQ manual:
for (r <- e
select (
T_BOOK.ID * T_BOOK.AUTHOR_ID,
T_BOOK.ID + T_BOOK.AUTHOR_ID * 3 + 4,
T_BOOK.TITLE || " abc" || " xy"
)
from T_BOOK
leftOuterJoin (
select (x.ID, x.YEAR_OF_BIRTH)
from x
limit 1
asTable x.getName()
)
on T_BOOK.AUTHOR_ID === x.ID
where (T_BOOK.ID <> 2)
or (T_BOOK.TITLE in ("O Alquimista", "Brida"))
fetch
) {
println(r)
}