Futures and lenses

futuresAndLenses.scala

scala> usernameToUserIdLens.get("Alan").foreach(println)
** SELECT ID FROM USERS WHERE NAME = Alan
1

scala> userIdToStreetNameLens.get(1).foreach(println)
** SELECT STREET_NAME FROM ADDRESS WHERE USER_ID = 1
High Street

scala> val usernameToStreetNameLens = usernameToUserIdLens >=> userIdToStreetNameLens

scala> usernameToStreetNameLens.get("Alan").foreach(println)
** SELECT ID FROM USERS WHERE NAME = Alan
** SELECT STREET_NAME FROM ADDRESS WHERE USER_ID = 1
High Street

scala> usernameToStreetNameLens.set("Alan", "New Street")
** SELECT ID FROM USERS WHERE NAME = Alan
** SELECT STREET_NAME FROM ADDRESS WHERE USER_ID = 1
** UPDATE ADDRESS SET STREET_NAME = New Street WHERE USER_ID = 1
res99: scala.concurrent.Future[String] = scala.concurrent.impl.Promise$DefaultPromise@11a0c15c
** UPDATE USERS SET NAME = Alan WHERE ID = 1

scala> usernameToStreetNameLens.get("Alan").foreach(println)
** SELECT ID FROM USERS WHERE NAME = Alan
** SELECT STREET_NAME FROM ADDRESS WHERE USER_ID = 1
New Street