Database Exception – yii\db\Exception

     * Returns the PDO instance for the currently active master connection.
     * This method will open the master DB connection and then return [[pdo]].
     * @return PDO the PDO instance for the currently active master connection.
     */
    public function getMasterPdo()
    {
        $this->open();
        return $this->pdo;
    }
 
    /**
     * Returns the currently active slave connection.
     * If this method is called for the first time, it will try to open a slave connection when [[enableSlaves]] is true.

     * is available and `$fallbackToMaster` is false.
     */
    public function getSlavePdo($fallbackToMaster = true)
    {
        $db = $this->getSlave(false);
        if ($db === null) {
            return $fallbackToMaster ? $this->getMasterPdo() : null;
        } else {
            return $db->pdo;
        }
    }
 
    /**

    public function quoteValue($str)
    {
        if (!is_string($str)) {
            return $str;
        }
 
        if (($value = $this->db->getSlavePdo()->quote($str)) !== false) {
            return $value;
        } else {
            // the driver doesn't support quote (e.g. oci)
            return "'" . addcslashes(str_replace("'", "''", $str), "\000\n\r\\\032") . "'";
        }
    }

     * @param string $value string to be quoted
     * @return string the properly quoted string
     * @see http://www.php.net/manual/en/function.PDO-quote.php
     */
    public function quoteValue($value)
    {
        return $this->getSchema()->quoteValue($value);
    }
 
    /**
     * Quotes a table name for use in a query.
     * If the table name contains schema prefix, the prefix will also be properly quoted.
     * If the table name is already quoted or contains special characters including '(', '[[' and '{{',

        $params = [];
        foreach ($this->params as $name => $value) {
            if (is_string($name) && strncmp(':', $name, 1)) {
                $name = ':' . $name;
            }
            if (is_string($value)) {
                $params[$name] = $this->db->quoteValue($value);
            } elseif (is_bool($value)) {
                $params[$name] = ($value ? 'TRUE' : 'FALSE');
            } elseif ($value === null) {
                $params[$name] = 'NULL';
            } elseif (!is_object($value) && !is_resource($value)) {
                $params[$name] = $value;

     * @return mixed the method execution result
     * @throws Exception if the query causes any problem
     * @since 2.0.1 this method is protected (was private before).
     */
    protected function queryInternal($method, $fetchMode = null)
    {
        $rawSql = $this->getRawSql();
 
        Yii::info($rawSql, 'yii\db\Command::query');
 
        if ($method !== '') {
            $info = $this->db->getQueryCacheInfo($this->queryCacheDuration, $this->queryCacheDependency);
            if (is_array($info)) {

     * @return array|false the first row (in terms of an array) of the query result. False is returned if the query
     * results in nothing.
     * @throws Exception execution failed
     */
    public function queryOne($fetchMode = null)
    {
        return $this->queryInternal('fetch', $fetchMode);
    }
 
    /**
     * Executes the SQL statement and returns the value of the first column in the first row of data.
     * This method is best used when only a single value is needed for a query.
     * @return string|null|false the value of the first column in the first row of the query result.

     */
    public function one($db = null)
    {
        if ($this->emulateExecution) {
            return false;
        }
        return $this->createCommand($db)->queryOne();
    }
 
    /**
     * Returns the query result as a scalar value.
     * The value returned will be the first column in the first row of the query results.
     * @param Connection $db the database connection used to generate the SQL statement.

     * @return ActiveRecord|array|null a single row of query result. Depending on the setting of [[asArray]],
     * the query result may be either an array or an ActiveRecord object. `null` will be returned
     * if the query results in nothing.
     */
    public function one($db = null)
    {
        $row = parent::one($db);
        if ($row !== false) {
            $models = $this->populate([$row]);
            return reset($models) ?: null;
        } else {
            return null;
        }

                break;
            }
        }
 
        $result = null;
 
        if ($runAction && $this->beforeAction($action)) {
            // run the action
            $result = $action->runWithParams($params);
 
            $result = $this->afterAction($action, $result);
 
            // call afterAction on modules

        $parts = $this->createController($route);
        if (is_array($parts)) {
            /* @var $controller Controller */
            list($controller, $actionID) = $parts;
            $oldController = Yii::$app->controller;
            Yii::$app->controller = $controller;
            $result = $controller->runAction($actionID, $params);
            if ($oldController !== null) {
                Yii::$app->controller = $oldController;
            }
 
            return $result;
        }

            $params = $this->catchAll;
            unset($params[0]);
        }
        try {
            Yii::trace("Route requested: '$route'", __METHOD__);
            $this->requestedRoute = $route;
            $result = $this->runAction($route, $params);
            if ($result instanceof Response) {
                return $result;
            } else {
                $response = $this->getResponse();
                if ($result !== null) {
                    $response->data = $result;

        try {
 
            $this->state = self::STATE_BEFORE_REQUEST;
            $this->trigger(self::EVENT_BEFORE_REQUEST);
 
            $this->state = self::STATE_HANDLING_REQUEST;
            $response = $this->handleRequest($this->getRequest());
 
            $this->state = self::STATE_AFTER_REQUEST;
            $this->trigger(self::EVENT_AFTER_REQUEST);
 
            $this->state = self::STATE_SENDING_RESPONSE;
            $response->send();