Call Solr asynchronous from Play Framework

Question

I have created a Play 2.1 Scala application. I am uncertain what's the best way to call Solr from a Play application:

• There is no Solr module for Play 2.
• AFAIK all Solr-APIs like SolrJ are blocking.
• I could wrap a SolrJ call into a Future, but this will also block a thread, correct?

• Should I use the play.api.libs.ws.WS library to call Solr and use Plays JSON support to extract the result (like in the example below) or is there any easier/faster way?

  val solrQuery: Future[play.api.libs.ws.Response] = WS.url("http://localhost:8983/solr/collection1/select?q=id%3A123&wt=json").get()
  

Answer 1

Here's how I use WS in my side project:

val itselfNodeFuture = Statix.doParams( Statix.SolrSelectWSReq, 
    List(
    "wt"     -> "json", 
    "q"      -> "*:*",
    "fq"     -> "node_type:collection",
    "fq"     -> "id:%d".format( nodeId),
    "indent" -> "true",
    "rows"   -> "1",
    "fl"     -> "id,parent_id,title",
    "fl"     -> "date_created,date_about,date_modified")
).get()

//Use the first Await after the last future
val itselfJson = Await.result(
    itselfNodeFuture, Duration("2 sec")).json

val mainRow = (itselfJson \ "response" \ "docs").as[ Seq[JsValue]]
val mainNodeParent = (mainRow(0) \ "parent_id").as[Long]
val mainNodeTitle = (mainRow(0) \ "title").as[String]

And here's the utility class I use, the doParams is especially useful.

object Statix { //Noder must extend this
    def SolrSelectWSReq = WS.url("http://127.0.0.1:8080/solr-store/collection1/select/")
    def SolrUpdateWSReq = WS.url("http://127.0.0.1:8080/solr-store/collection1/update/json/")

    def doParams(request: WS.WSRequestHolder, params: List[(String, String)]) = {
        params.foldLeft( request){
            (wsReq, tuple) => wsReq.withQueryString( tuple)}}
}

Answer 2

You want to wrap the call in a Future with its own Execution context. This way the call may be blocking, but it will use a different thread pool, not blocking the main application.

In fact, this is standard behaviour when facing blocking or slow tasks, like sending queries to a database or doing some heavy-lifting task.