Scala Slick Strategies For Composing Compiled Queries of various shapes -


i using postgresql 9.6, slick 3.2 , have slick-pg wired up.

i'm implementing graphql backend in scala , need implement queries resolve graphql cursors of various shapes. shapes of input enumerable. of inputs influencing query be:

  • a user selectable ordering.
  • various filtering criteria (full-text-search, date-ranges etc).
  • selecting between backward or forward traversal.

my current simple cursors have backward , forward hardcoded compiled queries. , both have same shape , using standard slick abstractions factor out commonality reuse (value classes ops, inheritance hierarchy "entity" tables , code generation). there still lot of boilerplate , won't scale more dynamic shapes unless list them out.

here excerpt class uses pattern:

private [shard] class schemaalltypecursor(shard: slickshard) extends cursorspec[typemodel] {   import shard.postgresprofile.api._   private val forwardqc = compiled { (tenantidurls: rep[list[string]], low: rep[long], take: constcolumn[long]) =>     queries.listtypesbytenantids(tenantidurls).forwardcursorbyid(low, take)   }   private val backwardqc = compiled { (tenantidurls: rep[list[string]], high: rep[long], take: constcolumn[long]) =>     queries.listtypesbytenantids(tenantidurls).backwardcursorbyid(high, take)   }    def executor(tenantidurls: list[string])(c: cursorrequest)(implicit req: req[_]): observable[typemodel] = {     implicit val ec = req.ctx.ec     observable fromfuture {       shard.db.run {         if (c.forward) forwardqc(tenantidurls, c.base, c.take).result         else backwardqc(tenantidurls, c.base, c.take).result       } flatmap materializealltypes(req.ctx, tenantidurls)     } flatmap observable.fromiterable   } }

the overall question how compiled queries use-case without mountains of boilerplate ? insights i'd gain is:

  1. what abstractions have composing parts of queries ? in example above backwardcursorbyid , forwardcursorbyid parts of query. i'm hoping able build compiled functions parts , cache them somehow....
  2. how use record type in compiled functions ? (it hinted in slick documentation possible, can't find examples).
  3. is there way caching compiled queries without listing them out ? -- afaik. if compile function in executor function above repeatedly compiled on each function invocation of executor function.

i open using postgres specific types supported slick-pg .


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