diff --git a/src/Contracts/StatisticsStore.php b/src/Contracts/StatisticsStore.php
index a5f6002..dc29a14 100644
--- a/src/Contracts/StatisticsStore.php
+++ b/src/Contracts/StatisticsStore.php
@@ -48,7 +48,8 @@ interface StatisticsStore
      * format that is easily to read for graphs.
      *
      * @param  callable  $processQuery
+     * @param  callable  $processCollection
      * @return array
      */
-    public function getForGraph(callable $processQuery = null): array;
+    public function getForGraph(callable $processQuery = null, callable $processCollection = null): array;
 }
diff --git a/src/Statistics/Stores/DatabaseStore.php b/src/Statistics/Stores/DatabaseStore.php
index 2a36529..042e72b 100644
--- a/src/Statistics/Stores/DatabaseStore.php
+++ b/src/Statistics/Stores/DatabaseStore.php
@@ -86,12 +86,13 @@ class DatabaseStore implements StatisticsStore
      * format that is easily to read for graphs.
      *
      * @param  callable  $processQuery
+     * @param  callable  $processCollection
      * @return array
      */
-    public function getForGraph(callable $processQuery = null): array
+    public function getForGraph(callable $processQuery = null, callable $processCollection = null): array
     {
         $statistics = collect(
-            $this->getRecords($processQuery)
+            $this->getRecords($processQuery, $processCollection)
         );
 
         return $this->statisticsToGraph($statistics);