Sunday, June 07, 2009

scouchdb Scala View Server gets "reduce"

scouchdb View Server gets reduce. After a fairly long hiatus, I finally got some time to do some hacking on scouchdb over the weekend. And this is what came out of a brief stint on Saturday evening ..

map was already supported in version 0.3. You could define map functions in Scala as ..

val mapfn = """(doc: dispatch.json.JsValue) => {
  val it = couch.json.JsBean.toBean(doc, classOf[couch.json.TestBeans.Item_1])._3;
  for (st <- it.prices)
    yield(List(it.item, st._2))
}"""


Now you can do reduce too ..

val redfn = """(key: List[(String, String)], values: List[dispatch.json.JsNumber], rereduce: Boolean) => {
  values.foldLeft(BigDecimal(0.00))
    ((s, f) => s + (match { case dispatch.json.JsNumber(n) => n }))
}"""


attach the map and reduce functions to a view ..

val view = new View(mapfn, redfn)


and finally fetch using the view query ..

val ls1 =
  couch(test view(
    Views.builder("big/big_lunch")
         .build))
ls1.size should equal(1)


reduce, by default returns only one row through a computation on the result set returned by map. The above query does not use grouping and returns 1 row as the result. You can also use view results grouping and return rows grouped by keys ..

val ls1 =
  couch(test view(
    Views.builder("big/big_lunch")
         .options(optionBuilder group(true) build) // with grouping
         .build))
ls1.size should equal(3)


For a more detailed discussion and examples have a look at the project home page documentation or browse through the test script ScalaViewServerSpec.

The current trunk is 0.3.1. The previous version has been tagged as 0.3 and available in tags folder.

Next up ..

  • JPA like collections of objects directly from scouchdb views

  • more capable reduce options (rereduce, collations etc.)

  • replication

  • advanced exception management with new dbDispatch


.. and lots of other features ..

Stay tuned!

1 comment:

martha said...

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Susan

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