From 2eedb1cf1c02c7bb43518bc45b3400f9adf1cd8b Mon Sep 17 00:00:00 2001
From: Brian Campbell <briancampbell@lucidchart.com>
Date: Tue, 8 May 2018 08:55:01 -0600
Subject: [PATCH] Provide a streaming result set

Allow users who want access to an underlying result set that is large to
do so through use of streamed statements
---
 .../scala/com/lucidchart/relate/SqlQuery.scala  | 16 ++++++++++++++++
 relate/src/test/scala/RelateITSpec.scala        | 17 +++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/relate/src/main/scala/com/lucidchart/relate/SqlQuery.scala b/relate/src/main/scala/com/lucidchart/relate/SqlQuery.scala
index 3dd2c45..d3f936f 100644
--- a/relate/src/main/scala/com/lucidchart/relate/SqlQuery.scala
+++ b/relate/src/main/scala/com/lucidchart/relate/SqlQuery.scala
@@ -79,6 +79,22 @@ trait Sql {
    */
   def results()(implicit connection: Connection): ResultSet = normalStatement.results()
 
+  /**
+    * Provides a java.sql.ResultSet that streams records from the database.
+    * This allows for interacting with large data sets with less risk of OutOfMemoryErrors.
+    * Many JDBC connectors will not allow for additional queries to the connection until the
+    * returned ResultSet has been closed.
+    * @param fetchSize the number of rows to fetch at a time, defaults to 100. If the JDBC Driver
+    * is MySQL, the fetchSize will always default to Int.MinValue, as MySQL's JDBC implementation
+    * ignores all other fetchSize values and only streams if fetchSize is Int.MinValue
+    * @param connection the db connection to use when executing the query
+    * @return java.sql.ResultSet that streams data from the database
+    */
+  def streamingResults(fetchSize: Int)(implicit connection: Connection): ResultSet = {
+    val prepared = streamedStatement(fetchSize)
+    prepared.results()
+  }
+
   /**
    * Execute a statement
    * @param connection the db connection to use when executing the query
diff --git a/relate/src/test/scala/RelateITSpec.scala b/relate/src/test/scala/RelateITSpec.scala
index 8164531..bf8c529 100644
--- a/relate/src/test/scala/RelateITSpec.scala
+++ b/relate/src/test/scala/RelateITSpec.scala
@@ -465,6 +465,23 @@ class RelateITSpec extends Specification with Db {
     }
   }
 
+  "results" should {
+    val ids = Array(1L, 2L, 3L)
+    "work from ResultSet" in withConnection { implicit connection =>
+      val resultSet = sql"SELECT * FROM pokedex WHERE id in ($ids)".results()
+      val pokemonNames = SqlResult(resultSet).asList(pokedexParser).map(_.name)
+
+      (pokemonNames must contain("Squirtle")) and (pokemonNames must contain("Wartortle")) and (pokemonNames must contain("Blastoise"))
+    }
+
+    "work from streaming ResultSet" in withConnection { implicit connection =>
+      val resultSet = sql"SELECT * FROM pokedex WHERE id in ($ids)".streamingResults(1)
+      val pokemonNames = SqlResult(resultSet).asList(pokedexParser).map(_.name)
+
+      (pokemonNames must contain("Squirtle")) and (pokemonNames must contain("Wartortle")) and (pokemonNames must contain("Blastoise"))
+    }
+  }
+
   "update" should {
     "update matched rows and not update unmatched rows" in withConnection { implicit connection =>
       val correct = List(