OpenMage#1167 - do not connect to write adapter when getting the read adapter (OpenMage#1169)

* OpenMage#1167 - do not connect to write adapter when getting the read adapter

* OpenMage#1167 - accidentally changed the return signature for _getReadAdapter()

Author: joshua-bn

app/code/core/Mage/Core/Model/Resource/Db/Abstract.php

@@ -324,18 +324,30 @@ protected function _getConnection($connectionName)
         return $this->_connections[$connectionName];
     }
 
+    /**
+     * @param string $connectionName
+     * @return bool
+     */
+    public function hasConnection($connectionName)
+    {
+        return isset($this->_connections[$connectionName]);
+    }
+
     /**
      * Retrieve connection for read data
      *
      * @return Magento_Db_Adapter_Pdo_Mysql
      */
     protected function _getReadAdapter()
     {
-        $writeAdapter = $this->_getWriteAdapter();
-        if ($writeAdapter && $writeAdapter->getTransactionLevel() > 0) {
-            // if transaction is started we should use write connection for reading
-            return $writeAdapter;
+        if ($this->hasConnection('write')) {
+            $writeAdapter = $this->_getWriteAdapter();
+            if ($writeAdapter && $writeAdapter->getTransactionLevel() > 0) {
+                // if transaction is started we should use write connection for reading
+                return $writeAdapter;
+            }
         }
+
         return $this->_getConnection('read');
     }