minor adjustment of db exception.

framework/db/Command.php

@@ -134,7 +134,7 @@ class Command extends \yii\base\Component
 			} catch (\Exception $e) {
 				\Yii::error($e->getMessage() . "\nFailed to prepare SQL: $sql", __CLASS__);
 				$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
-				throw new Exception($e->getMessage(), (int)$e->getCode(), $errorInfo);
+				throw new Exception($e->getMessage(), $errorInfo, (int)$e->getCode());
 			}
 		}
 	}
@@ -292,7 +292,7 @@ class Command extends \yii\base\Component
 			\Yii::error("$message\nFailed to execute SQL: {$sql}{$paramLog}", __CLASS__);
 
 			$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
-			throw new Exception($message, (int)$e->getCode(), $errorInfo);
+			throw new Exception($message, $errorInfo, (int)$e->getCode());
 		}
 	}
 
@@ -431,7 +431,7 @@ class Command extends \yii\base\Component
 			$message = $e->getMessage();
 			\Yii::error("$message\nCommand::$method() failed: {$sql}{$paramLog}", __CLASS__);
 			$errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;
-			throw new Exception($message, (int)$e->getCode(), $errorInfo);
+			throw new Exception($message, $errorInfo, (int)$e->getCode());
 		}
 	}
 

framework/db/Connection.php

@@ -320,7 +320,7 @@ class Connection extends Component
 	{
 		if ($this->pdo === null) {
 			if (empty($this->dsn)) {
-				throw new InvalidConfigException('Connection.dsn cannot be empty.');
+				throw new InvalidConfigException('Connection::dsn cannot be empty.');
 			}
 			try {
 				\Yii::trace('Opening DB connection: ' . $this->dsn, __CLASS__);
@@ -330,7 +330,7 @@ class Connection extends Component
 			catch (\PDOException $e) {
 				\Yii::error("Failed to open DB connection ({$this->dsn}): " . $e->getMessage(), __CLASS__);
 				$message = YII_DEBUG ? 'Failed to open DB connection: ' . $e->getMessage() : 'Failed to open DB connection.';
-				throw new Exception($message, (int)$e->getCode(), $e->errorInfo);
+				throw new Exception($message, $e->errorInfo, (int)$e->getCode());
 			}
 		}
 	}

framework/db/Exception.php

@@ -24,13 +24,14 @@ class Exception extends \yii\base\Exception
 	/**
 	 * Constructor.
 	 * @param string $message PDO error message
-	 * @param integer $code PDO error code
 	 * @param mixed $errorInfo PDO error info
+	 * @param integer $code PDO error code
+	 * @param \Exception $previous The previous exception used for the exception chaining.
 	 */
-	public function __construct($message, $code = 0, $errorInfo = null)
+	public function __construct($message, $errorInfo = null, $code = 0, \Exception $previous = null)
 	{
 		$this->errorInfo = $errorInfo;
-		parent::__construct($message, $code);
+		parent::__construct($message, $code, $previous);
 	}
 
 	/**

framework/db/mysql/QueryBuilder.php

@@ -52,7 +52,7 @@ class QueryBuilder extends \yii\db\QueryBuilder
 		$quotedTable = $this->db->quoteTableName($table);
 		$row = $this->db->createCommand('SHOW CREATE TABLE ' . $quotedTable)->queryRow();
 		if ($row === false) {
-			throw new Exception("Unable to find '$oldName' in table '$table'.");
+			throw new Exception("Unable to find column '$oldName' in table '$table'.");
 		}
 		if (isset($row['Create Table'])) {
 			$sql = $row['Create Table'];