Ralph Ralph - 3 months ago 23
Scala Question

Treating an SQL ResultSet like a Scala Stream

When I query a database and receive a (forward-only, read-only) ResultSet back, the ResultSet acts like a list of database rows.

I am trying to find some way to treat this ResultSet like a Scala

Stream
. This will allow such operations as
filter
,
map
, etc., while not consuming large amounts of RAM.

I implemented a tail-recursive method to extract the individual items, but this requires that all items be in memory at the same time, a problem if the ResultSet is very large:

// Iterate through the result set and gather all of the String values into a list
// then return that list
@tailrec
def loop(resultSet: ResultSet,
accumulator: List[String] = List()): List[String] = {
if (!resultSet.next) accumulator.reverse
else {
val value = resultSet.getString(1)
loop(resultSet, value +: accumulator)
}
}

Answer

I didn't test it, but why wouldn't it work?

new Iterator[String] {
  def hasNext = resultSet.next()
  def next() = resultSet.getString(1)
}.toStream