From e105d925cf295b125d695daba959679d5aa77356 Mon Sep 17 00:00:00 2001
From: Mark Pavlitski <markpavlitski@gmail.com>
Date: Thu, 16 May 2013 21:21:36 +0100
Subject: [PATCH] Issue #238250 by markpavlitski: Check bin is a cache table
 before truncating.

---
 includes/cache.inc | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/includes/cache.inc b/includes/cache.inc
index f76164b..96a4aa5 100644
--- a/includes/cache.inc
+++ b/includes/cache.inc
@@ -505,7 +505,12 @@ class DrupalDatabaseCache implements DrupalCacheInterface {
     else {
       if ($wildcard) {
         if ($cid == '*') {
-          db_truncate($this->bin)->execute();
+          // Check if $this->bin is a cache table before truncating. Other
+          // cache operations throw a PDO error in this situation, so we don't
+          // need to verify them first.
+          if ($this->isValidBin()) {
+            db_truncate($this->bin)->execute();
+          }
         }
         else {
           db_delete($this->bin)
@@ -542,4 +547,18 @@ class DrupalDatabaseCache implements DrupalCacheInterface {
       ->fetchField();
     return empty($result);
   }
+
+  /**
+   * Checks if $this->bin represents a valid cache table.
+   *
+   * @return boolean
+   */
+  function isValidBin() {
+    // These fields are required for any cache table.
+    $fields = array('cid', 'data', 'expire', 'created', 'serialized');
+    // Load the table schema.
+    $schema = drupal_get_schema($this->bin);
+    // Confirm that all fields are present.
+    return !array_diff($fields, array_keys($schema['fields']));
+  }
 }
-- 
1.8.1.2