Fixes discouraged static table object and SlickDDLPlugin when referri…

…ng to vals in AutoDDL

* Replace static singleton table objects with vale. From the Slick docs "Also make sure that an actual object for a table is not defined in a static location (i.e. at the top level or nested only inside other objects) because this can cause problems in certain situations due to an overeager optimization performed by scalac. Using a val for your table (with an anonymous structural type or a separate class definition) is fine everywhere." http://slick.typesafe.com/doc/1.0.1/lifted-embedding.html#tables
* SlickDDLPlugin now handles LinkageError, which can happen, when referring to vals in AutoDDL, because it is loaded via reflection.

samples/computer-database/app/models/AutoDDL.scala

@@ -2,6 +2,6 @@ package play.api.db.slick
 object AutoDDL extends AutoDDLInterface{
   import models._
   def tables = Map(
-  	"default" -> Seq(Companies,Computers)
+  	"default" -> Seq(new Companies,new Computers)
   )
 }

samples/computer-database/app/models/Models.scala

@@ -17,7 +17,7 @@ case class Company(id: Option[Long], name: String)
 
 case class Computer(id: Option[Long] = None, name: String, introduced: Option[Date]= None, discontinued: Option[Date]= None, companyId: Option[Long]=None)
 
-object Companies extends Table[Company]("COMPANY") {
+class Companies extends Table[Company]("COMPANY") {
 
   def id = column[Long]("id", O.PrimaryKey, O.AutoInc)
   def name = column[String]("name", O.NotNull)
@@ -47,7 +47,7 @@ object Companies extends Table[Company]("COMPANY") {
   }
 }
 
-object Computers extends Table[Computer]("COMPUTER") {
+class Computers extends Table[Computer]("COMPUTER") {
 
   implicit val javaUtilDateTypeMapper = MappedTypeMapper.base[java.util.Date, java.sql.Date](
     x => new java.sql.Date(x.getTime),

samples/computer-database/app/models/package.scala

@@ -0,0 +1,4 @@
+package object models{
+  val Companies = new Companies
+  val Computers = new Computers
+}

samples/play-slick-sample/app/models/AutoDDL.scala

@@ -2,6 +2,6 @@ package play.api.db.slick
 object AutoDDL extends AutoDDLInterface{
   import models._
   def tables = Map(
-  	"default" -> Seq(Cats)
+  	"default" -> Seq(new Cats)
   )
 }

samples/play-slick-sample/app/models/Cat.scala

@@ -4,7 +4,7 @@ import play.api.db.slick.Config.driver._
 
 case class Cat(name: String, color: String)
 
-object Cats extends Table[Cat]("CAT") {
+class Cats extends Table[Cat]("CAT") {
 
   def name = column[String]("name", O.PrimaryKey)
   def color = column[String]("color", O.NotNull)

samples/play-slick-sample/app/models/package.scala

@@ -0,0 +1,4 @@
+package object models{
+  // Slick table objects should not be static singleton objects, because of a Scala bug. Use vals instead.
+  val Cats = new Cats
+}

src/main/scala/play/api/db/slick/SlickPlugin.scala

@@ -19,7 +19,7 @@ trait AutoDDLInterface{
 class SlickDDLPlugin(app: Application) extends Plugin {
   private val CreatedBy = "# --- Created by Slick DDL"
   private val configKey = "slick.autoddl_dbs"
-  def confError(msg:String) = app.configuration.reportError(configKey, msg)
+  def confError(msg:String,e:Option[Throwable]=None) = app.configuration.reportError(configKey, msg, e)
 
   override def onStart(): Unit = {
     app.configuration
@@ -76,14 +76,28 @@ class SlickDDLPlugin(app: Application) extends Plugin {
 
   /** generates DDL for given datasource */
   def evolutionScript(db:String): Option[String] = {
-    val ddls = 
-          fetchAutoDDLobject
-          .tables
-          .get(db)
-          .map(_.map(_.ddl))
-          .getOrElse{
-            throw confError(s"play.api.db.slick.AutoDDL.tables did not contain datasource '$db'")
-          }
+    val tables =
+      try{
+        fetchAutoDDLobject.tables
+      } catch {
+        case e:java.lang.LinkageError =>
+          throw confError(
+            s"LinkageError when trying to load play.api.db.slick.AutoDDL.tables via reflection: '$e'."
+            +" In the definition of play.api.db.slick.AutoDDL.tables you probably referred to a val,"
+            +" which was not yet initialized. Please refer to defs, singleton objects or alternatively"
+            +" instantiate the table objects right in the definiton, e.g. like "+"""
+               def tables = Map(
+                 "default" -> Seq(new MyTableA,new MyTableB)
+               )"""
+            , Some(e)
+          )
+      }
+    val ddls = tables
+               .get(db)
+               .map(_.map(_.ddl))
+               .getOrElse{
+                 throw confError(s"play.api.db.slick.AutoDDL.tables did not contain datasource '$db'")
+               }
 
     val delimiter = ";" //TODO: figure this out by asking the db or have a configuration setting?