Backporting fix of issue laravel#9251 to 5.1 branch. Original commit …

…by Taylor Otwell: d9e0a6a

src/Illuminate/Session/DatabaseSessionHandler.php

@@ -4,6 +4,7 @@
 
 use Carbon\Carbon;
 use SessionHandlerInterface;
+use Illuminate\Database\QueryException;
 use Illuminate\Database\ConnectionInterface;
 
 class DatabaseSessionHandler implements SessionHandlerInterface, ExistenceAwareInterface
@@ -95,16 +96,45 @@ public function read($sessionId)
     public function write($sessionId, $data)
     {
         if ($this->exists) {
-            $this->getQuery()->where('id', $sessionId)->update([
-                'payload' => base64_encode($data), 'last_activity' => time(),
-            ]);
+            $this->performUpdate($sessionId, $data);
         } else {
-            $this->getQuery()->insert([
+            $this->performInsert($sessionId, $data);
+        }
+
+        $this->exists = true;
+    }
+
+
+    /**
+     * Perform an insert operation on the session ID.
+     *
+     * @param  string  $sessionId
+     * @param  string  $data
+     * @return void
+     */
+    protected function performInsert($sessionId, $data)
+    {
+        try {
+            return $this->getQuery()->insert([
                 'id' => $sessionId, 'payload' => base64_encode($data), 'last_activity' => time(),
             ]);
+        } catch (QueryException $e) {
+            $this->performUpdate($sessionId, $data);
         }
+    }
 
-        $this->exists = true;
+    /**
+     * Perform an update operation on the session ID.
+     *
+     * @param  string  $sessionId
+     * @param  string  $data
+     * @return int
+     */
+    protected function performUpdate($sessionId, $data)
+    {
+        return $this->getQuery()->where('id', $sessionId)->update([
+            'payload' => base64_encode($data), 'last_activity' => time(),
+        ]);
     }
 
     /**