server: Improve the ColumnNameResolver

In order to get deterministic results while retrieving
paginated results, the getUniqueColumnName method has been
introduced, when sorting by a non-unique column, we'll break
ties using the unique column.

server/app/com/xsn/explorer/data/anorm/interpreters/ColumnNameResolver.scala

@@ -7,5 +7,13 @@ import scala.annotation.implicitNotFound
 )
 trait ColumnNameResolver[A] {
 
+  /**
+   * Maps a field to the column name on the sql schema.
+   */
   def getColumnName(field: A): String
+
+  /**
+   * This is used to break ties while sorting by non-unique fields,
+   */
+  def getUniqueColumnName: String
 }

server/app/com/xsn/explorer/data/anorm/interpreters/FieldOrderingSQLInterpreter.scala

@@ -7,8 +7,13 @@ class FieldOrderingSQLInterpreter {
   def toOrderByClause[A](fieldOrdering: FieldOrdering[A])(implicit columnNameResolver: ColumnNameResolver[A]) = {
     val field = columnNameResolver.getColumnName(fieldOrdering.field)
     val condition = getCondition(fieldOrdering.orderingCondition)
+    val uniqueField = columnNameResolver.getUniqueColumnName
 
-    s"ORDER BY $field $condition"
+    if (field == uniqueField) {
+      s"ORDER BY $field $condition"
+    } else {
+      s"ORDER BY $field $condition, $uniqueField"
+    }
   }
 
   private def getCondition(ordering: OrderingCondition) = ordering match {

server/app/com/xsn/explorer/models/fields/BalanceField.scala

@@ -19,8 +19,13 @@ object BalanceField {
     case _ => None
   }
 
-  implicit val columnNameResolver: ColumnNameResolver[BalanceField] = (field) => field match {
-    case Available => s"(${Received.string} - ${Spent.string})"
-    case f => f.string
+  implicit val columnNameResolver: ColumnNameResolver[BalanceField] = new ColumnNameResolver[BalanceField] {
+
+    override def getUniqueColumnName: String = Address.string
+
+    override def getColumnName(field: BalanceField): String = field match {
+      case Available => s"(${Received.string} - ${Spent.string})"
+      case f => f.string
+    }
   }
 }