Interpolation support for Traversable[SQLSyntax]

[pheaver]

Sometimes I want to render SQL like this:

(a, b) IN ((1, 2), (3, 4), (5, 6))

To do that, I would expect something like this to work:

val columns: Seq[SQLSyntax] = Seq("a", "b").map(SQLSyntax.createUnsafely(_, Nil))
val values: Seq[SQLSyntax] = Seq(Seq(1, 2), Seq(3, 4), Seq(5, 6)).map { xs => sqls"($xs)" }
sqls"$columns IN ($values)"

However, the implementation in SQLInterpolationString treats all Traversables the same, without looking at whether the arguments are SQLSyntax, so that will actually render to the following SQL:

(?, ?) IN (?, ?, ?)

I believe this can be fixed like this:

private def addPlaceholders(sb: StringBuilder, param: Any): StringBuilder = param match {
  case _: String => sb += '?'
  case t: Traversable[_] => t.map(addPlaceholders(new StringBuilder, _)).addString(sb, ", ")
  case LastParameter => sb
  case SQLSyntax(s, _) => sb ++= s
  case _ => sb += '?'
}

private def buildParams(params: Traversable[Any]): Seq[Any] = params.foldLeft(Seq.newBuilder[Any]) {
  case (b, s: String) => b += s
  case (b, t: Traversable[_]) => b ++= buildParams(t)
  case (b, SQLSyntax(_, params)) => b ++= params
  case (b, n) => b += n
}.result()

I tested these definitions and it worked for the few examples I tried.

[seratch]

That sounds cool. If you have time, please send a pull request. Or you can leave it to me.

[pheaver]

Ok I will do a pull request soon.